Key points

Thomson → discovered the electron (cathode rays, 1897)

Rutherford → discovered the nucleus (alpha scattering experiment, 1911)

Bohr → quantised energy levels (1913), ΔE = hν

Quantum mechanical model → probability clouds (orbitals), 4 quantum numbers, Pauli exclusion principle

Isotope → same Z (protons), different N → Example: I-123, I-125, I-131

Isobar → same A (mass), different Z → Example: Mo-99, Tc-99

Isotone → same N (neutrons), different Z

Isomer → same Z and A, different energy state → Example: Tc-99m / Tc-99

1 amu = 931.5 MeV

Electron/positron mass = 0.511 MeV

Annihilation photon energy = 511 keV (each)

β⁺ decay threshold = 1.022 MeV

Tc-99m gamma energy = 140 keV

I-131 gamma energy = 364 keV

Strong nuclear force → holds the nucleus together

Weak nuclear force → responsible for beta decay

Electromagnetic force → repulsion between protons (Coulomb)

Gravitational force → negligible on the nuclear scale

Magic numbers: 2, 8, 20, 28, 50, 82, 126

Example of a doubly magic nucleus: Pb-208 (Z=82, N=126)

Even–even nuclei are the most stable, odd–odd the least stable

Only 4 stable odd–odd nuclei in nature: ²H, ⁶Li, ¹⁰B, ¹⁴N

Fe-56 → highest BE/A → most stable nucleus

Neutron excess → β⁻ decay (e.g. I-131, Mo-99)

Proton excess → β⁺ or EC (e.g. F-18 → β⁺, Tl-201 → EC, Ga-67 → EC)

Heavy nucleus (Z > 83) → α decay (e.g. Ra-223, Ra-226)

Excited nucleus → isomeric transition/internal conversion (e.g. Tc-99m → IT)

Low Z → Auger electron dominates

High Z → characteristic X-ray dominates

Kα X-ray = E_K − E_L; KLL Auger electron ≈ E_K − 2E_L

I-125 → Auger emitter → high-LET-like effect when close to DNA

U-238 → Pb-206

U-235 → Pb-207

Th-232 → Pb-208 (doubly magic)

Maximum electrons = 2n²

K=2, L=8, M=18, N=32

Neutron excess → β⁻ decay → Z increases by 1, A unchanged

Proton excess → β⁺ or EC → Z decreases by 1, A unchanged

Heavy nucleus (Z > 83) → α decay → Z decreases by 2, A decreases by 4

Excited nucleus → isomeric transition (IT) → Z and A unchanged

β⁺ threshold: 1.022 MeV → below the threshold only EC occurs

β⁻: n → p + e⁻ + ν̄ₑ → Z increases → an antineutrino is emitted

β⁺: p → n + e⁺ + νₑ → Z decreases → a neutrino is emitted → threshold: 1.022 MeV

EC: p + e⁻ → n + νₑ → Z decreases → a neutrino is emitted → no threshold

β⁻ and β⁺: continuous energy spectrum

EC: monoenergetic neutrino + characteristic X-ray/Auger

Monoenergetic: alpha particles, internal conversion electrons, gamma rays, Auger electrons, characteristic X-rays

Continuous spectrum: beta particles (β⁻ and β⁺), bremsstrahlung X-rays

Y-90 (Emax = 2.28 MeV, T½ = 64.1 h)

P-32 (Emax = 1.71 MeV, T½ = 14.3 days)

Sr-89 (Emax = 1.46 MeV, T½ = 50.5 days)

Sr-90 (Emax = 0.546 MeV, T½ = 28.8 years)

Pure beta emitters cannot be imaged directly → bremsstrahlung SPECT; for Y-90 also PET via internal pair production

Rb-82: 75 seconds (shortest, cardiac PET)

A = λN = (0.693/T½) × N

A(t) = A₀ × e^−λt = A₀ × (1/2)^t/T½

1 Ci = 3.7 × 10¹⁰ dps = 37 GBq

1 mCi = 37 MBq

1 µCi = 37 kBq

Mean beta energy = Emax/3

Te = (Tp × Tb) / (Tp + Tb)

Te is always shorter than both Tp and Tb

The shorter half-life determines the effective half-life more

τ = 1/λ = 1.443 × T½

τ is always longer than T½

Cumulated activity: Ã = A₀ × τ = 1.443 × A₀ × T½

Transient equilibrium: T½(parent) > T½(daughter), same order → A(daughter) > A(parent) → Example: Mo-99/Tc-99m

Secular equilibrium: T½(parent) >> T½(daughter) → A(daughter) = A(parent) → Example: Sr-82/Rb-82, Ge-68/Ga-68

No equilibrium: T½(daughter) > T½(parent) → no equilibrium is established

Other examples of secular equilibrium: Ra-226/Rn-222 (classic example in nature) and the Rb-81/Kr-81m generator

Transient equilibrium

At equilibrium the Tc-99m/Mo-99 ratio is theoretically 1.1; with 87.5% branching actually ≈0.96

tmax ≈ 23 h

At tmax ideally A(daughter) = A(parent); for Mo/Tc A(Tc) ≈ 0.88 × A(Mo)

At equilibrium Tc-99m decreases with the half-life of Mo-99 (66 h)

Daily elution (~24 h) is close to tmax → optimal yield

F-18 < C-11 < N-13 < O-15 ≈ Ga-68 < Rb-82

Short range → good resolution

F-18: best resolution

Rb-82: poorest resolution

Arrow down to the right → β⁻ (Z increases)

Arrow down to the left → β⁺ or EC (Z decreases)

Vertical arrow down → IT or gamma (Z unchanged)

Top line → parent nucleus

Bottom line → daughter ground state

Intermediate lines → excited states

High Z

Low transition energy

Large change in angular momentum (ΔL)

IC and Auger electrons are absorbed locally in tissue → no contribution to imaging, they only increase the patient dose

F-18: 96.7% β⁺ + 3.3% EC

Cu-64: 17.6% β⁺ + 38.5% β⁻ + 43.9% EC (a rare radionuclide with both β⁺ and β⁻ decay)

Tc-99m: ~100% IT → of which 88.5% is 140 keV gamma emission + 11.5% internal conversion (IC)

Activity (Bq) = decay rate ≠ photon emission rate → number of photons = activity × gamma yield

1 MBq Tc-99m → ~0.89 × 10⁶ 140 keV photons/s

Positron + electron → short-lived positronium → annihilation → 2 × 511 keV (~180°)

Alpha: Heavy (4 amu), +2e charge, straight path, short range (~50 µm in tissue), high LET (~80 keV/µm), has a Bragg peak, shielding: paper/skin is enough

Beta: Light (0.000549 amu ≈ 1/1836 of the proton mass), ±1e charge, tortuous path, longer range (a few mm in tissue), low LET (~0.2 keV/µm), no Bragg peak, shielding: Perspex (low Z)

Photon: Massless, uncharged, exponential attenuation, no concept of range (HVL is used), low LET, shielding: lead (high Z)

Bremsstrahlung ∝ Z × E (high Z and high energy → more bremsstrahlung)

Beta shielding → low Z (Perspex) → bremsstrahlung minimised

Gamma shielding → high Z (lead) → photoelectric absorption maximised

Two-layer shielding (for pure beta emitters): inner = Perspex (stops beta) + outer = lead (shields bremsstrahlung)

Pure beta emitters: Y-90, P-32, Sr-89 → Perspex shield essential

Photoelectric: ∝ Z³/E³ → dominant at high Z, low E → photon completely absorbed → NO scattered photon

Compton: independent of Z, depends on density → dominant at intermediate E → photon partly absorbed → scattered photon PRESENT

Pair production: ∝ Z² → threshold: 1.022 MeV → dominant at high E, high Z → e⁻/e⁺ pair is created

Coherent: low E, high Z → NO energy transfer → direction changes

Soft tissue (Z ≈ 7.4): ~30 keV → Compton → ~20 MeV

Bone (Z ≈ 14): ~50 keV → Compton → ~15 MeV

Lead (Z = 82): ~500 keV → Compton → ~5 MeV

Board rule: at nuclear medicine energies (70-511 keV) Compton ALWAYS dominates in soft tissue

Above the K-edge the probability of the photoelectric effect rises abruptly

Compton formula: E′ = E / [1 + (E/511)(1 − cos θ)]

180° backscatter: E′ = E / [1 + 2E/511]

140 keV → 180° backscatter → ~91 keV (scattered photon), ~49 keV (Compton electron)

511 keV → 180° backscatter → ~170 keV (scattered photon), ~341 keV (Compton electron)

θ = 0° → no energy transfer (E' = E)

θ = 180° → maximum energy transfer

Tc-99m (140 keV): 0.3 mm Pb

Tl-201 (69-83 keV X-rays): 0.2 mm Pb

I-131 (364 keV): 3 mm Pb

F-18 (511 keV): 4 mm Pb

Cs-137 (662 keV): 6.5 mm Pb

Co-60 (1.25 MeV): 12 mm Pb

Rule: HVL increases with energy (thicker shielding needed)

HVL = 0.693 / µ = ln2 / µ

TVL = 2.303 / µ = ln10 / µ

TVL = 3.32 × HVL

Fraction transmitted after n HVL = (1/2)ⁿ

1 HVL → 50%, 2 HVL → 25%, 3 HVL → 12.5%, 4 HVL → 6.25%, 5 HVL → 3.125%

Formula: I₁ × d₁² = I₂ × d₂²

Distance 2× → dose 1/4

Distance 3× → dose 1/9

Distance 4× → dose 1/16

Distance 10× → dose 1/100

Valid only for point sources

Line source: 1/d, plane source: ~constant at close range

Tl-201 (0.45) < Ga-67 (0.76) < Tc-99m (0.78) < I-131 (2.17) < In-111 (3.21) < Cs-137 (3.26) < F-18 (5.73) < Ra-226 (8.25) < Co-60 (13.2)

Formula: Ḋ = Γ × A / d²

Higher Γ → higher dose for the same activity → more protection needed

PET radiopharmaceuticals (F-18) have a higher Γ than SPECT agents (Tc-99m) → staff dose is higher in PET

Time: Reduce the time → D = Ḋ × t

Distance: Move away → inverse square law (most effective and cheapest method)

Shielding: Choose a suitable material (gamma → Pb, beta → Perspex, alpha → prevent contamination, neutron → hydrogen-rich material)

Activity: Use the lowest diagnostic dose

Training: Train the staff

W value: Average energy needed to create one ion pair = ~34 eV (in air, approximately the same for all types of radiation)

LET: Energy transferred to the medium per unit path length (keV/µm) → varies with the type of radiation

Specific ionisation: Number of ion pairs per unit path length → alpha >> beta

The W value is constant; LET and specific ionisation depend on the type of radiation

Stopping power ∝ z²/v² (Bethe–Bloch) → with the same mass and velocity, a 2-fold charge reduces the range to ~1/4

Delta (δ) rays: secondary electrons ejected by the primary charged particle that can themselves cause ionisation

Narrow beam: B = 1 (scattered photons do not reach the detector)

Broad beam: B > 1 (scattered photons also contribute)

B increases with material thickness

B must be taken into account in radiation protection calculations → otherwise shielding will be inadequate

X-ray spectrum: continuous part → bremsstrahlung; sharp peaks → characteristic X-rays

Maximum photon energy = tube voltage (120 kV → 120 keV)

Total number of photons ∝ mA × kV²

Difference between X-ray and gamma → origin (outside the nucleus vs nucleus), not energy

Ionisation threshold: 13.6 eV; EURATOM: ≤100 nm (≥3 × 10¹⁵ Hz)

Imaging windows: X-ray (CT, SPECT, PET), radiofrequency (MR), ultrasound (US)

511 keV photons in soft tissue: >95% Compton

Direct action: Radiation → direct DNA damage → dominant at high LET → independent of oxygen

Indirect action: Radiation → radiolysis of water → OH• radical → DNA damage → dominant at low LET (~70%) → oxygen-dependent

Most important free radical: OH• (hydroxyl radical)

Oxygen fixation hypothesis: O₂ makes free radical damage permanent

Base damage: Most frequent, most easily repaired, usually not lethal

SSB: Frequent (~1000/Gy), easily repaired (opposite strand as template), usually not lethal

DSB: Rare (~40/Gy), difficult to repair, the MOST IMPORTANT cause of cell death

Clustered damage: Characteristic of high LET, very difficult to repair, most lethal

BER: Single-base damage → fast, efficient

NER: Bulky lesions (UV damage) → defective in xeroderma pigmentosum

HR: DSB repair → error-free → only in S/G2 phase → BRCA1/2 required

NHEJ: DSB repair → error-prone → active in all phases → the dominant DSB repair pathway in mammalian cells

MMR: Replication errors → defective in Lynch syndrome

Mitotic death: The most frequent type of radiation-induced death → death during division

Apoptosis: Programmed death → p53-mediated → dominant in lymphocytes (interphase death)

Necrosis: Disordered death → at very high doses

Senescence: Permanent arrest of division → the cell is alive but does not divide

SF = e−(αD + βD²)

α/β ratio = the dose at which the linear and quadratic components are equal

High α/β (~10 Gy): Early-responding tissue, tumours → little shoulder → little affected by fractionation

Low α/β (~2-3 Gy): Late-responding tissue → marked shoulder → strongly affected by fractionation

Exception: Prostate cancer has a low α/β (~1.5-3 Gy) → behaves like a late-responding tissue

Most sensitive: M phase and late G2

Most resistant: Late S phase (HR active, repair enzymes high)

Intermediate: G1 phase

G0: Usually radioresistant (non-dividing cells)

Most sensitive → Most resistant: Lymphocyte > Spermatogonia > Erythroblast > Intestinal crypt > Basal epidermis > Endothelium >

Exception to Bergonié-Tribondeau: Lymphocytes are very radiosensitive despite high differentiation (apoptosis) LET – RBE – OER Relationship (Golden Triangle)

LET↑ → RBE↑ (up to 100 keV/µm, then overkill → RBE↓)

LET↑ → OER↓ (the oxygen effect disappears at high LET)

Optimal LET: ~100 keV/µm → maximum RBE

Low LET (gamma, X-ray): RBE = 1, OER ≈ 2.5-3.0, indirect action dominant

High LET (alpha): RBE ≈ 20, OER ≈ 1.0, direct action dominant

X-ray / Gamma: RBE = 1 (reference)

Beta: RBE ≈ 1

Proton: RBE ≈ 1.1

Thermal neutron: RBE ≈ 2-5

Fast neutron: RBE ≈ 10-20

Alpha: RBE ≈ 20

RBE formula: RBE = reference dose / test dose (for the same biological effect)

Deterministic: Threshold PRESENT → severity increases with dose → cell death → early or late (e.g. cataract, fibrosis) effect → predictable → Examples: cataract, epilation, sterility, erythema, radiation syndromes

Stochastic: NO threshold (LNT) → probability increases with dose (not severity) → cell mutation → late effect → unpredictable at the individual level → Examples: cancer, hereditary effects

Cataract threshold: ~0.5 Gy (ICRP 118 update – this value is asked in the exam!)

Radiation-associated leukaemias: AML, CML, ALL → CLL is NOT radiation-associated

Radiation does not create new types of mutation; it increases the frequency of spontaneous mutations (most are recessive)

LNT: Standard for stochastic effects → accepted by the ICRP → basis of radiation protection regulations

Threshold model: Applies to deterministic effects

Hormesis: Protective effect at low dose → controversial → not used in regulations

BEIR VII (atomic bomb data): leukaemia risk linear-quadratic, solid cancer risk linear

Haematopoietic syndrome: 1-8 Gy → bone marrow → pancytopenia → LD₅₀/₆₀ ≈ 3.5-4.5 Gy (untreated)

GI syndrome: 8-30 Gy → intestinal crypt → bloody diarrhoea, sepsis → death at ~10-14 days

Neurovascular syndrome: >30 Gy → CNS → convulsions, coma → death within 24-72 hours → no treatment

Four clinical phases: Prodromal → Latent → Manifest illness → Recovery/Death

Early onset of prodromal symptoms = indicator of high dose

1. Lymphocyte (hours-days) → FASTEST → biological dosimeter 2. Neutrophil (2-3 weeks) 3. Platelet (3-4 weeks) 4. Erythrocyte (last – lifespan ~120 days) → SLOWEST

1. Repair: Sublethal damage repair → spares late-responding tissues 2. Reassortment (Redistribution): Transition from the resistant S phase to the sensitive G2/M → against the tumour 3. Repopulation: Surviving cells multiply → in favour of normal tissue, against tumour control (tumour cells also multiply; becomes marked as treatment time lengthens)

4. Reoxygenation: Hypoxic cells become oxygenated → radiosensitivity increases → against the tumour

Preimplantation (0-9 days): "All or none" → death or normal development

Organogenesis (2-8 weeks): HIGHEST risk of congenital anomalies → teratogenic period

Early fetal (8-15 weeks): HIGHEST risk of mental retardation → period of neuronal migration → ~25-30 IQ points/Gy lost

Late fetal (16-25 weeks): Lower risk of mental retardation → ~10-13 IQ points/Gy lost

>25 weeks: Very low risk of marked anomalies/mental retardation → childhood cancer risk (stochastic)

<50 mGy: NO INDICATION for therapeutic abortion

I-131 therapy is ABSOLUTELY CONTRAINDICATED in pregnancy (the fetal thyroid concentrates iodine after weeks 10-12)

Amifostine (WR-2721): The most important clinical radioprotector → free radical scavenger → selectively protects normal tissue → FDA approved (prevention of xerostomia)

Amifostine does not cross the blood-brain barrier → does not protect the CNS; most marked protection in the salivary glands and kidney

Oxygen: The most potent natural radiosensitiser

Hypoxic cell sensitisers: Misonidazole, nimorazole → mimic oxygen

Halogenated pyrimidines: BrdU, IdU → incorporated into DNA → effective only in the S phase

D₀: Dose that reduces survival to 37% → low D₀ = high radiosensitivity

Dq: Shoulder width → large Dq = good repair capacity

n: Extrapolation number → if n = 1 there is no shoulder (high LET)

High LET: No shoulder, curve steep from the start, n ≈ 1

Low LET: Marked shoulder, the curve starts shallow then steepens

SLDR (sublethal damage repair): Repair between two fractions (~6 hours) → Elkind recovery → marked at low LET

PLDR (potentially lethal damage repair): Repair possible if division is delayed → marked in slow-growing tumours → a cause of radioresistance

Low dose rate → time for repair → survival increases → biological effect decreases

High dose rate → insufficient repair → damage accumulates → biological effect increases

Inverse dose-rate effect: At low dose rate cells accumulate in G2/M → paradoxically more death (in some tumour lines)

1. Physical stage: ~10⁻¹⁸ – 10⁻¹² seconds → ionisation/excitation → SHORTEST 2. Chemical stage: ~10⁻¹² – 10⁻² seconds → free radical formation 3. Biological stage: Seconds – years → DNA repair, cell death, cancer → LONGEST

Adaptive response → 1-100 mGy priming dose followed by protection

Bystander → response in a non-irradiated neighbouring cell; Abscopal → immune-mediated response in a distant metastasis (DAMP)

ICRP 103 nominal risk: cancer ~5.5%/Sv, heritable ~0.2%/Sv

<100 mGy → no clinically relevant functional impairment expected in any tissue

Optimal LET ~100 keV/µm → ionisation spacing = DNA diameter; Auger electrons in the high-LET group; TAT ~100 keV/µm

BED = n·d·[1 + d/(α/β)] → comparison of radionuclide therapies

Intrinsic apoptosis → cytochrome c/Apaf-1/caspase 9; extrinsic → caspase 8

Hypoxia → HIF-1α → VEGF (VEGFR-2); Warburg effect → FDG uptake

Somatostatin receptor = GPCR; PD-1 (T cell) – PD-L1 (tumour)

"Most important free radical?" → OH• (hydroxyl radical)

"Most important cause of cell death?" → DSB (double-strand break)

"Most radiosensitive somatic cell?" → Lymphocyte

"Most radioresistant somatic cell?" → Nerve cell (neuron)

"Most radiosensitive cell cycle phase?" → M phase (and late G2)

"Most radioresistant cell cycle phase?" → Late S phase

"Most frequent type of radiation-induced cell death?" → Mitotic death

"Type of death in lymphocytes?" → Apoptosis (interphase death)

"Radiation protection model?" → LNT (Linear No-Threshold Model)

"Clinical radioprotector?" → Amifostine (WR-2721)

"Most potent natural radiosensitiser?" → Oxygen

"First cell to fall in ARS?" → Lymphocyte

"Last cell to fall in ARS?" → Erythrocyte

"Most sensitive period for mental retardation?" → 8-15 weeks (early fetal)

"Most sensitive period for congenital anomalies?" → 2-8 weeks (organogenesis)

"Effect of radiation in preimplantation?" → All or none

"DSB repair mechanism active in all phases?" → NHEJ

"Error-free DSB repair mechanism?" → HR (only S/G2)

"Exception to Bergonié-Tribondeau?" → Lymphocyte (radiosensitive despite high differentiation)

Ionisation chamber: NO gas amplification → current mode → energy-independent → dose calibrator, survey meter, pocket dosimeter

Proportional counter: Gas amplification PRESENT (10³-10⁶) → pulse mode → CAN discriminate energy → alpha-beta discrimination, neutron detection

GM counter: Maximum amplification (10⁸-10¹⁰) → pulse mode → CANNOT discriminate energy → most sensitive → longest dead time (~100-300 µs) → contamination survey

Recombination → Ionisation → Proportional → Limited proportional → Geiger-Müller → Continuous discharge

NaI(Tl): Gamma camera standard → highest light output among classical scintillators → energy resolution ~10% → hygroscopic → 3/8-inch thickness (for Tc-99m)

BGO: Older PET crystal → highest effective Z → best stopping power → BUT slow (300 ns) → CANNOT do TOF → low light output

LSO/LYSO: Modern PET standard → fast (~40 ns) → TOF-PET possible → high light output → Lu-176 background activity

CZT: Semiconductor → best energy resolution (in clinical use) → direct conversion → no PMT needed → compact → expensive

HPGe: Absolutely the best energy resolution → BUT cooling needed (77 K) → no clinical use

PMT: High gain (10⁶-10⁷) → SENSITIVE to magnetic fields → cannot be used in PET/MR → large size → high voltage (~1000-2000 V)

SiPM: High gain (10⁶) → INSENSITIVE to magnetic fields → used in PET/MR → compact → low voltage (~30-70 V) → dark current (noise) → temperature-sensitive

Dose calibrator → Radiopharmaceutical activity measurement (µCi-mCi)

Well counter → In vitro sample activity measurement (nCi-pCi)

GM counter → Contamination survey

Gamma probe → Intraoperative sentinel lymph node localisation

Thyroid uptake probe → Measurement of thyroid iodine uptake

LSC (liquid scintillation counter) → H-3, C-14 (low-energy beta emitters)

Proportional counter → Alpha-beta discrimination, neutron detection

Detection efficiency = geometric efficiency × intrinsic efficiency; increasing the distance lowers only the geometric efficiency

Well counter: dead-time loss at >~1 µCi; geometric efficiency falls as sample volume increases → standard and sample are counted in the same volume/tube

RIA (competitive): count INVERSELY proportional to antigen; IRMA (sandwich, non-competitive): count DIRECTLY proportional to antigen, more sensitive

Photopeak: Photoelectric interaction → all energy deposited → imaging is based on this peak

Compton edge/plateau: Compton scattering → partial energy deposited

Iodine escape peak: Photopeak – 28 keV ( 112 keV for Tc-99m)

Backscatter peak: 180° scattering from outside the crystal

Sum peak: Pile-up → photopeak × 2 (at high count rate)

Compton edge + backscatter peak = photopeak energy (Tc-99m: ~50 + ~90 keV; Cs-137: 478 + 184 keV)

%FWHM varies as ≈ 1/√E → energy resolution worsens at low energy (Tl-201 > Tc-99m > I-131)

Standard: Photopeak ± 10% = 20% window

Tl-201: 70 keV-centred 30% window (~60-81 keV) + a 20% window at 167 keV

Narrow window → contrast↑, sensitivity↓

Wide window → sensitivity↑, contrast↓

Standard deviation: σ = √N

Relative standard deviation: σ/N = 1/√N

95% confidence interval: N ± 2√N

99% confidence interval: N ± 2.58√N (±3√N ≈ 99.7%)

If you increase the count 4 times → the standard deviation increases 2 times → the relative standard deviation halves

Paralysable system: Count rate↑↑ → paradoxical fall in count (paralysis) → DANGEROUS (high radiation appears as a low count)

Non-paralysable system: Count rate↑↑ → plateau (the count does not rise but does not fall either)

Gamma camera: Paralysable

GM counter: Non-paralysable

Dead time correction formula: Ntrue = Nmeasured / (1 - Nmeasured × τ)

Density/Z → detection efficiency; light output → energy and timing resolution; decay time → speed

SPECT: single-piece crystal; PET: pixelated crystal array separated by reflector

SiPM/APD → Geiger mode; digital SiPM → each cell digitised separately → CTR ~130 ps

Multi-pinhole CZT (19 cameras) → no light sharing; D-SPECT → 9 rotating columns, high sensitivity

"Activity meter" instead of "dose calibrator" (the device measures activity)

Gamma probe → relative quantification by count rate; endoscopic/robotic models available

"With which device is radiopharmaceutical activity measured?" → Dose calibrator

"What type of detector is the dose calibrator?" → Well-type ionisation chamber (pressurised gas)

"Is there gas amplification in the dose calibrator?" → NO

"Gamma camera crystal?" → NaI(Tl)

"Activator of NaI(Tl)?" → Thallium (Tl)

"Most important disadvantage of NaI(Tl)?" → Hygroscopic

"Crystal thickness in the gamma camera?" → 3/8 inch (~9.5 mm)

"Modern standard crystal in PET?" → LSO/LYSO

"Crystal for TOF-PET?" → LSO/LYSO (short decay time ~40 ns)

"Why can BGO not do TOF?" → Decay time too long (300 ns)

"Detector with the best energy resolution?" → HPGe (cooling needed) → CZT in clinical use

"Photodetector in PET/MR?" → SiPM (insensitive to magnetic fields)

"Why can PMTs not be used in PET/MR?" → Sensitive to magnetic fields

"Gas-filled detector that cannot discriminate energy?" → GM counter

"Device for contamination survey?" → GM counter

"Measurement of H-3 (tritium)?" → Liquid scintillation counter (LSC)

"Counting of in vitro blood samples?" → Well counter (NaI well counter)

"Intraoperative localisation of the sentinel lymph node?" → Gamma probe

"Tc-99m energy window?" → 140 keV ± 10% (20% window)

"Iodine escape peak (Tc-99m)?" → 112 keV (140 - 28)

"Standard deviation of 10,000 counts?" → √10,000 = 100

"Gas-filled detector with the longest dead time?" → GM counter (~100-300 µs)

"What happens in a paralysable system at a high count rate?" → Paradoxical fall in count (paralysis)

"Most common source of error in the dose calibrator?" → Wrong radionuclide setting (dial setting)

"In which mode does the dose calibrator work?" → Current mode (NOT pulse mode)

"What type of detector is the well counter?" → NaI(Tl) scintillation detector (well-type)

"In which mode does the well counter work?" → Pulse mode

"Difference between the well counter and the dose calibrator?" → Well counter: scintillation, pulse mode, low activity (nCi-pCi). Dose calibrator: ionisation chamber, current mode, high activity (µCi-mCi)

"Why is a quenching gas needed in a GM counter?" → The positive ion cloud must be quenched to prevent continuous discharge → halogen (unlimited lifetime) or organic (limited lifetime ~10⁹ counts)

"Difference between the proportional counter and the GM counter?" → The proportional counter CAN discriminate energy (pulse size proportional to energy); the GM counter CANNOT

"What does yellowing of a NaI(Tl) crystal mean?" → Moisture damage (the hygroscopic crystal has absorbed moisture → the crystal is degraded → must be replaced)

"Disadvantage of LSO/LYSO?" → Natural radioactivity of Lu-176 → background activity

"What happens if the crystal thickness in the gamma camera is increased?" → Sensitivity increases (more photons absorbed) BUT intrinsic spatial resolution decreases

"What happens if the crystal thickness in the gamma camera is reduced?" → Intrinsic spatial resolution increases BUT sensitivity decreases (fewer photons absorbed)

"Energy resolution formula?" → (FWHM / E₀) × 100 (%)

"Most important factor affecting energy resolution?" → Statistical fluctuations (variation in the number of signal units produced)

"Difference between SCA and MCA?" → SCA: Single energy window (gamma camera). MCA: multichannel full spectrum (spectroscopy, radionuclide identification)

"With which device is a wipe test sample counted?" → Well counter or LSC (depending on the radionuclide)

NaI(Tl): Density 3.67 g/cm³ | Zeff 50 | Decay time 230 ns | Energy resolution ~10% (140 keV)

BGO: Density 7.13 g/cm³ | Zeff 74 | Decay time 300 ns | Energy resolution ~20% (511 keV)

LSO: Density 7.4 g/cm³ | Zeff 66 | Decay time 40 ns | Energy resolution ~10-12% (511 keV)

LYSO: Density 7.1 g/cm³ | Zeff 65 | Decay time 41 ns | Energy resolution ~10-12% (511 keV)

CZT: Density 5.8 g/cm³ | Zeff ~50 | Energy resolution ~5-6% (140 keV)

HPGe: Density 5.32 g/cm³ | Z 32 | Energy resolution ~0.2-0.5% | Cooling: 77 K (liquid nitrogen)

Gas (air): ~34 eV/ion pair

NaI(Tl) scintillation: ~20-30 eV/light photon (effective)

Semiconductor (Si): ~3.6 eV/electron-hole pair

Semiconductor (Ge): ~2.96 eV/electron-hole pair

Semiconductor (CZT): ~4.6 eV/electron-hole pair

Most sensitive gas-filled detector → GM counter

Best energy resolution (overall) → HPGe

Best energy resolution (clinical) → CZT

Best energy resolution (gas-filled) → Proportional counter

Longest dead time → GM counter (~100-300 µs)

Shortest dead time → Semiconductor detectors (~ns)

Highest light output (classical scintillators: NaI, BGO, LSO/LYSO, GSO) → NaI(Tl) (LaBr₃/CeBr₃ and CsI(Tl) are higher; see Chapter 28)

Highest density (PET crystal) → LSO (~7.4 g/cm³)

Highest Zeff (PET crystal) → BGO (74)

Shortest decay time (PET crystal) → LSO/LYSO (~40 ns)

First commercial SPECT/CT: GE, 1999 → low-dose single-slice CT (~3.5 mm)

The effective dose contribution of CT is ~1-10 mSv; low-mAs CT is often sufficient for localisation/AC

HU = [(µ_tissue − µ_water)/µ_water] × 1000; HU → µ conversion is bilinear (with a phantom)

Misregistration: Respiration (SPECT averaged vs CT instantaneous), table sag, axial centre offset

Truncation, beam hardening, metal, iodinated contrast → AC artefacts

Dosimetry: VOIs are drawn on CT → transferred to SPECT; successive time points are aligned by CT–CT non-rigid registration

Dedicated brain SPECT (ring) ~3 mm; whole-body SPECT ~7-12 mm

Inventor of the gamma camera: Hal Anger (1958)

Signal flow: Gamma photon → Collimator → Crystal (NaI(Tl)) → Light guide → PMT → Position calculation (X,Y) →

Energy analysis (Z pulse) → Image

Standard crystal thickness: 3/8 inch (~9.5 mm) → optimised for Tc-99m (140 keV)

Number of PMTs: Typically 37-91, hexagonal array

Z pulse = ΣSᵢ → represents the photon energy

Anger logic: X, Y position calculated by the weighted mean (centroid) method

Tc-99m (140 keV) → LEHR (bone, thyroid) or LEAP (dynamic studies)

Tl-201 (70-167 keV) → LEHR or LEAP

Ga-67 (93-300 keV) → ME (Medium Energy)

In-111 (171-245 keV) → ME (Medium Energy)

I-131 (364 keV) → HE (High Energy)

Thyroid (small organ) → Pinhole

The only collimator that inverts the image → Pinhole

Collimators that magnify → Pinhole (at close range) and converging

Collimator that minifies → Diverging

Distance↑ → collimator whose sensitivity stays constant → Parallel-hole

Distance↑ → collimator whose resolution and sensitivity both decrease → Pinhole

Most widely used collimator → Parallel-hole (LEHR)

Rc = d × (L + z) / L

d: hole diameter, L: hole length, z: source-collimator distance

z↑ → Rc↑ (worsens) | d↑ → Rc↑ (worsens) | L↑ → Rc↓ (improves)

If the hole diameter is increased 2 times → sensitivity increases ~4 times and resolution worsens ~2 times (sensitivity ∝ Rc²)

Pinhole/converging magnification (M) reduces the intrinsic resolution contribution to Ri/M → for a close object the system resolution may be better than the intrinsic resolution

Rs = √(Rᵢ² + Rc²)

Rc >> Rᵢ → The collimator is the limiting component

Cardiac SPECT: 180° acquisition (RAO 45° → LPO 45°), 90° (L-mode) dual-head, 64×64 matrix

General SPECT (bone, brain): 360° acquisition, 180° configuration dual-head, 128×128 matrix

Body-contour orbit → distance minimised → resolution optimised

Step-and-shoot → the most common acquisition mode

Cardiac SPECT slice planes: SA (short axis), VLA (vertical long axis), HLA (horizontal long axis)

The two basic functions of CT: Anatomical localisation + attenuation correction (CTAC)

CTAC principle: CT HU values → converted into µ values appropriate to the SPECT photon energy → attenuation map

Metallic implant → streak artefact on CT → falsely high HU → overcorrection for attenuation → hot artefact (spuriously increased uptake)

IV contrast → same mechanism → hot artefact → solution: non-contrast CT or acquire CT before contrast

Misregistration → SPECT-CT mismatch → wrong anatomical localisation + incorrect attenuation correction → cause: patient motion, respiration

NOT an advantage of SPECT/CT → increased temporal resolution (on the contrary, temporal mismatch is a disadvantage)

Component limiting total resolution → Collimator (Rc >> Rᵢ)

Total resolution formula → Rs = √(Rᵢ² + Rc²)

Most important daily quality control test → Uniformity

Measurement of intrinsic uniformity → Collimator REMOVED + point source (at 5 × FOV from the crystal)

Measurement of system (extrinsic) uniformity → Collimator FITTED + flood source

Most common cause of non-uniformity → PMT gain drift

Order of corrections → First energy → then linearity → then uniformity

Dead-time behaviour of the gamma camera → Paralysable (extendable) → paradoxical fall in counts at very high count rate (paralysis)

Sensitivity-resolution relationship → Inversely proportional (trade-off) → determined by collimator selection

LEHR: Best resolution / lowest sensitivity

LEHS: Best sensitivity / lowest resolution

LEAP: Intermediate balance

Tc-99m: 140 keV ± 10% (20% window)

I-131: 364 keV ± 10% (20% window)

Tl-201: 70 keV + 167 keV (dual window)

Ga-67: 93 + 185 + 300 keV (triple window)

In-111: 171 + 245 keV (dual window)

Narrow window → scatter rejection↑ → contrast↑ → sensitivity↓

Wide window → sensitivity↑ → scatter↑ → contrast↓

Two radionuclides on the same day: lower energy first, then higher energy (downscatter avoided; e.g. Xe-133 ventilation → Tc-99m MAA perfusion)

Thick crystal → Sensitivity↑ + intrinsic resolution↓ → for high-energy radionuclides

Thin crystal → Sensitivity↓ + intrinsic resolution↑ → for low-energy radionuclides

Standard 3/8 inch → optimal for Tc-99m (140 keV) → absorbs ~90% of the photons

The same crystal absorbs only ~30% of the 364 keV photons of I-131 (intrinsic efficiency falls with energy)

NEMA: CFOV = 75% of the linear dimensions of the UFOV; 9-point filter before calculation

Signs of crystal damage: Yellow discoloration (yellowing), cold spots, non-uniformity → cannot be repaired, must be replaced Frequently Asked "Which One?" Exam Questions – Quick Answer Cards

1. "The most important component determining the spatial resolution of the gamma camera?" → Collimator 2. "The most important component determining the sensitivity of the gamma camera?" → Collimator 3. "The most important daily quality control test?" → Uniformity 4. "The most common cause of non-uniformity?" → PMT gain drift 5. "The collimator that inverts the image?" → Pinhole 6. "The collimator used in thyroid scintigraphy?" → Pinhole 7. "The collimator whose sensitivity does not change with distance?" → Parallel-hole 8. "The collimator whose resolution and sensitivity both decrease with distance?" → Pinhole 9. "Acquisition angle in cardiac SPECT?" → 180° (RAO 45° → LPO 45°) 10. "Detector configuration in cardiac SPECT?" → 90° (L-mode) 11. "Standard crystal thickness?" → 3/8 inch (~9.5 mm) 12. "What does the Z pulse represent?" → Photon energy 13. "Dead-time type of the gamma camera?" → Paralysable 14. "Order of corrections?" → Energy → Linearity → Uniformity 15. "Metallic implant artefact in SPECT/CT?" → Hot artefact (spuriously increased uptake) 16. "Collimator for Ga-67?" → ME (Medium Energy) 17. "Collimator for I-131?" → HE (High Energy) 18. "If a high-energy radionuclide is imaged with a low-energy collimator?" → Septal penetration → star artefact

19. "Advantage of the converging collimator?" → Higher sensitivity than the parallel-hole collimator 20. "Why is the body-contour orbit preferred?" → Detector-patient distance minimised → resolution optimised

PET/CT ~2001 (Townsend); CT replaced the Ge-68 transmission scan, which took up to 15 min

TOF routine since 2006; LAFOV 1-2 m → ~1-2 mSv or <5 min whole body

Gating: list mode; cardiac → ECG, respiratory → pneumatic belt

PET/MR: Siemens 2011 (APD, no TOF), GE 2014 (SiPM, with TOF)

DPC: SiPM microcell binary output; energy = number of cells fired

MR coils and the table also contribute to 511 keV attenuation; CT-derived µ map in the phantom

CTDI (16/32 cm phantom, mGy) ≠ patient dose; DLP = CTDI × length

Iterative reconstruction → noise↓, resolution preserved, dose↓; PCCT → photon counting, spectral imaging

MR: ω = γB₀; clinical 1.5-3 T; k-space → Fourier transform

Molecular sensitivity: PET > SPECT >> MRI

Annihilation photon energy: 511 keV (each)

Angle between the two photons: ~180°

Angular deviation (acolinearity): ±0.25°

Effect of acolinearity on resolution: ~2 mm (in a PET of 80 cm diameter)

F-18: 0.6 mm → BEST resolution

Rb-82: 5.9 mm → WORST resolution

Rule to memorise: energy↑ → range↑ → resolution↓

True: Same event, correct LOR → the desired event

Scatter: Same event, scattered photon → wrong LOR → loss of contrast

Random: Different events, chance pairing → wrong LOR → homogeneous noise

Multiple: 3+ photons at once → event rejected

Random correction method: Delayed window

Random ∝ A² (quadratic), True ∝ A (linear)

Highest stopping power: BGO (highest effective Z)

Most widely used: LSO / LYSO

Most suitable for TOF-PET: LSO / LYSO (short decay time ~40 ns)

Why BGO is not suitable for TOF: Long decay time (300 ns)

Disadvantage of LSO: Natural Lu-176 radioactivity (intrinsic background)

Best energy resolution: NaI(Tl) (~8%) → but insufficient stopping power for PET

Light detector in PET/MR: SiPM (insensitive to magnetic fields)

Why PMTs cannot be used in PET/MR: Sensitive to magnetic fields

PET: Electronic collimation (coincidence detection) → NO physical collimator

SPECT: Physical collimator required

PET sensitivity ~10-100 times higher than SPECT

PET spatial resolution: ~4-6 mm (clinical) vs SPECT: ~8-12 mm

PET: 511 keV photons vs SPECT: the gamma energy of the radionuclide (usually 70-364 keV)

Position calculation: Δx = c × Δt / 2

SNR gain: √(D / Δx)

Most marked advantage in obese patients (D large → gain large)

Required for TOF: Fast crystal (LSO/LYSO) + SiPM + fast electronics

200 ps → Δx = 3 cm

400 ps → Δx = 6 cm

TOF does not directly improve spatial resolution (Δx is at the cm level); the gain is in SNR/effective sensitivity, contrast and lesion detectability

PET energy window typically ~425/435-650 keV (LSO/LYSO); if the lower threshold is lowered, scatter acceptance increases

Bilinear transformation: conversion from CT energy (~70-140 keV) to the µ value at 511 keV

SUVbw falsely high in an obese patient → solution: SUVlean

HU > 0: Different curve (soft tissue-bone)

Metallic implant → falsely high HU → CTAC overcorrection → hot artefact

Contrast medium → falsely high HU → hot artefact

Respiratory misregistration → cold band at the diaphragm base or hot artefact at the lung base

Verification: Always compare with NAC (non-attenuation-corrected) images

NAC image: skin and lung activity high, centre of the body faint/periphery bright

CT parameters: mAs↑ → dose↑ linearly, noise ∝ 1/√mAs, contrast unchanged; kVp↑ → noise↓, contrast↓, dose↑; pitch↑ → dose↓

Most important technical challenge: MRAC (MR-based attenuation correction)

The MRAC problem: bone and air are signal-free on MR → cannot be distinguished → bone attenuation is undercorrected

Most common MRAC method: Dixon-based segmentation (4 classes: air, lung, fat, soft tissue)

Methods that solve the bone problem: UTE/ZTE, atlas-based, deep learning

Light detector in PET/MR: SiPM (the PMT cannot work in the magnetic field)

Advantages of PET/MR: Superior soft-tissue contrast, lower radiation dose, simultaneous acquisition, functional MR

Areas where PET/CT is superior: Lung nodules, cortical bone lesions, speed/practicality, RT planning

Strong indications for PET/MR: Neurology, paediatric oncology, pelvic tumours, head and neck, liver

SUV formula: Tissue activity concentration / (Injected activity / Body weight)

Most common variant: SUVmax (single voxel, operator-independent)

PERCIST variant: SULpeak (lean body mass + 1 cm³ spherical VOI)

"Why is SUV falsely high in an obese patient?" → Fat does not take up FDG but is included in the weight → use SUVlean

Increases SUV: Long uptake time, inflammation, high tumour grade

Decreases SUV: Hyperglycaemia (the most important!), small lesion (PVE), extravasation, short uptake time

Partial volume effect: Lesion < 2-3 × resolution (~8-10 mm) → SUV lower than it is

TLG = MTV × SUVmean

Standard uptake time: 60 ± 10 minutes

Dual-time-point imaging: the late SUV usually rises in malignancy, but it also rises in inflammation → limited value in differentiation

Fasting: Minimum 4-6 hours

Upper limit of blood glucose: 150-200 mg/dL

Hyperglycaemia → tumour SUV↓ → false negative

Insulin should not be given immediately before FDG → muscle uptake↑ (FDG ≥4 hours after short-acting insulin)

Reducing brown fat (BAT): Warm environment, propranolol, diazepam

BAT locations: Supraclavicular, cervical, paravertebral, mediastinal → bilateral symmetrical

After G-CSF: Wait at least 2 weeks (bone marrow uptake)

After chemotherapy: At least 2-3 weeks (ideally 6 weeks)

After radiotherapy: At least 2-3 months

Rebound thymic hyperplasia: Diffuse mediastinal uptake in a young patient after chemotherapy → false positive

2D: Septa present → scatter↓, randoms↓ → but sensitivity↓ → no longer used

3D: No septa → sensitivity ~4-8-fold↑ → but scatter↑ (30-40%), randoms↑ → the standard today

"Is there a collimator in PET?" → NO (electronic collimation)

"With which radionuclide is PET resolution best?" → F-18

"With which radionuclide is PET resolution worst?" → Rb-82

"Why is TOF more advantageous in an obese patient?" → D large → √(D/Δx) large

"How do you verify a CTAC artefact?" → Compare with NAC images

"Why is bone a problem in PET/MR?" → Bone is signal-free on MR → confused with air → undercorrection

"What happens in hyperglycaemia?" → Tumour SUV↓ → false negative

HU ≤ 0: One curve (air-soft tissue)

Photopeak window typically 10-20%; for 128 × 128 SPECT, 120 projections over 360° are sufficient

Static / dynamic (1-5 s frames) / list mode (event-based, clinical in PET) / gated (ECG, respiratory)

In PET, attenuation → depends on body size; in SPECT → depends on depth (Tc-99m brain: counts may fall by >4-fold)

Partial volume → <2 × FWHM; more pronounced in SPECT; large ROI → total activity correct, mean concentration low

Patlak → Ki (irreversible); Logan → V_T (reversible); 2-compartment/4-constant → specific binding

FBP: Analytical solution → fast → 1/r correction with ramp filter → noise-sensitive → streak artefacts → may produce negative values → limited modelling of physical factors → limited use today

MLEM: Iterative → Poisson statistics → multiplicative update → no negative values → all projection data in every iteration → very slow → not suitable for clinical use

OSEM: Accelerated version of MLEM → division into subsets → acceleration ≈ number of subsets → standard today → typical: 2-4 iterations × 8-16 subsets

Effective iterations = number of iterations × number of subsets

Iterations↑ → resolution↑, contrast↑, noise↑

Iterations↓ → noise↓, resolution↓, contrast↓

Chang: Post-reconstruction → uniform µ assumption → simple → specific to SPECT → inaccurate in the thorax (lung–soft tissue difference)

CTAC: Intra-reconstruction → non-uniform µ map → CT HU → bilinear conversion → voxel-based → most accurate → standard in PET/CT and SPECT/CT

Transmission source: Ge-68 or Cs-137 → old PET method → no longer used

MRAC: In PET/MR → Dixon segmentation → bone problem → solved with UTE/ZTE/atlas/deep learning

Attenuation correction is mandatory in PET (photon pair attenuation, independent of source position)

Attenuation correction is recommended in SPECT but not mandatory

Tc-99m (140 keV) µ ≈ 0.15 cm⁻¹ | 511 keV µ ≈ 0.096 cm⁻¹

SPECT: TEW (triple energy window) → 3 windows → trapezoidal approximation → standard

PET: SSS (Single Scatter Simulation) → Klein-Nishina → analytical → standard

Scatter fraction: SPECT ~30-40% | 3D PET ~30-50% | 2D PET ~15-20%

Cardiac gating: ECG → R-R interval → 8 or 16 frames → LVEF = (EDV-ESV)/EDV × 100

Respiratory gating: Respiratory sensor → 4-10 phases → most stable phase: end-expiration

Dual gating: Cardiac + respiratory → best correction → too many bins → noise → limited clinical use

Arrhythmia management: Beat rejection (±20% acceptance window)

Tachycardia → short R-R → short frame duration → temporal sampling becomes difficult

Arrhythmia → rejected beats → loss of counts, gating artefact

Ramp filter: Specific to FBP → H(f) = |f| → 1/r correction → high-frequency amplification → noise↑ → not used alone → window function needed

Butterworth: Most common → cutoff frequency + order → cutoff frequency↑ → resolution↑, noise↑

Gaussian: Common in PET → FWHM parameter → FWHM↑ → smoothing↑ → no ringing artefact

Hanning/Hamming: Window functions → used with the ramp in FBP

Order of smoothing at the same cutoff frequency: Ramp < Shepp-Logan < Hamming < Hanning < Parzen (Parzen smoothest, lowest resolution)

Prefiltering (to 2D projections before reconstruction) vs postfiltering (to the 3D volume after reconstruction)

Low frequencies = signal (general structure) | High frequencies = detail + noise

Pixel size ≤ 1/2 - 1/3 of FWHM (Nyquist criterion)

Nyquist frequency = 1 / (2 × pixel size)

SPECT matrix: 64 × 64 or 128 × 128

PET matrix: 128 × 128 – 400 × 400

Pixel depth: byte (8-bit) → at most 255 counts/pixel; word (16-bit) → 65,535

Pixel size = FOV / (matrix × zoom) → zoom makes the pixel smaller and narrows the displayed field

Number of SPECT projections: 60-128 (360°)

Too few projections → streak artefacts

Preferred orbit: Body contouring

Step-and-shoot vs continuous: Step-and-shoot → less angular blurring

Improves resolution → partial volume effect decreases → SUV may increase

Most important artefact: Gibbs artefact (Gibbs ringing) → ring at the edges of hot spots

Consistent reconstruction parameters must be used in follow-up studies

Point source → sinusoidal curve

Point source at the centre of rotation → straight vertical line

Sinogram = 2D matrix display of projection data from all angles (x: detector position, y: angle)

The sinogram is the input data of the reconstruction algorithm

1D Fourier transform of a projection profile = a line through the 2D Fourier space of the image at that angle

It is the mathematical basis of FBP

Thanks to this theorem, the frequency-space representation is obtained from projection data → the image is formed by the inverse Fourier transform

Intra-reconstruction correction: CTAC (included in the system matrix in iterative reconstruction) → applied during reconstruction

Post-reconstruction correction: Chang method → the image is formed first, then multiplied by the correction matrix

Ramp filter ≠ Butterworth filter: Ramp → 1/r correction (specific to FBP); Butterworth → noise reduction (smoothing)

MLEM ≠ OSEM: MLEM → all projection data in every iteration → slow; OSEM → division into subsets → fast

TEW ≠ SSS: TEW → SPECT scatter correction; SSS → PET scatter correction

Noise ≠ Resolution: Iterations↑ → both increase (trade-off); cutoff frequency↓ → both decrease

Effective iterations = Number of iterations × Number of subsets

LVEF = (EDV − ESV) / EDV × 100

Nyquist frequency = 1 / (2 × pixel size)

Pixel size ≤ FWHM / 2 (ideal: FWHM / 3)

Chang correction factor: C(x,y) = 1 / [1/N × Σ e^−µ·dᵢ]

Butterworth: H(f) = 1 / √[1 + (f/f_c)²ⁿ]

Gaussian: H(f) = e^{−2π²σ²f²}, FWHM = 2.355 × σ

Ramp: H(f) = |f|

PET attenuation correction factor: ACF = e^(+µ·D) → independent of source position

1. The standard reconstruction algorithm in SPECT and PET today → OSEM 2. Attenuation correction in PET → mandatory (CTAC standard) 3. Attenuation correction in SPECT → recommended (Chang or CTAC) 4. SPECT scatter correction → TEW 5. PET scatter correction → SSS 6. Most common filter → Butterworth 7. Number of frames in gated SPECT → 8 or 16 8. Most stable phase in respiratory gating → end-expiration 9. Artefact of PSF modelling → Gibbs ringing 10. Point source in the sinogram → sinusoidal curve

Spatial resolution is measured by FWHM → smaller FWHM = better resolution

System resolution = √(R²intrinsic + R²collimator) → collimator resolution dominates

The factor that most affects collimator resolution → source–collimator distance

Sensitivity and resolution are inversely related (trade-off)

With a parallel-hole collimator, sensitivity is independent of distance; resolution worsens with distance

Dominant noise source in nuclear medicine → statistical (Poisson) noise (σ = √N)

SNR = √N → if counts increase 4-fold, SNR increases 2-fold

Rose criterion: CNR ≥ 3-5 → required for reliable lesion detection

Partial volume effect: Lesion < 2-3 × FWHM → in a hot lesion SUV↓ (spill-out), in a cold lesion SUV↑ (spill-in)

Recovery coefficient (RC) = measured / true concentration; in a small lesion RC < 1 → corrected value = measured / RC

The system MTF is the product of the component MTFs → the total MTF is lower even than the weakest component

FWTM/FWHM > ~1.83 (Gaussian) → long tail → septal penetration/scatter

With the same total counts, the relative noise of a SPECT slice is higher than planar (reconstruction amplifies noise)

Upward creep: Gradual upward shift of the diaphragm after exercise → inferior wall artefact → solution: wait 15-30 min or prone position

Breast attenuation: Woman → fixed anterior wall defect

Diaphragmatic attenuation: Man → fixed inferior wall defect

Distinguishing attenuation artefact from true defect: 1) CTAC, 2) Prone position, 3) Gated analysis (wall motion/thickening)

Brown adipose tissue (BAT): Symmetric cervical/supraclavicular FDG uptake → reduced with propranolol, warm environment

Suppression of myocardial FDG: Prolonged fasting (≥12-18 hours) + high-fat diet

Ring artefact (SPECT) → non-uniformity (PMT gain difference, crystal defect)

COR error: Small → blurring; large → donut artefact (different from ring artefact!)

PMT failure: Focal cold (gain loss) or hot (gain increase) area on the flood image

Energy window shift: General loss of counts, non-uniformity → prevented by daily peaking

Metallic implant: High HU → overcorrection → spuriously increased uptake → verify with the NAC image

IV contrast: High intravascular HU in the bolus phase → spuriously increased uptake (especially SVC, subclavian vein)

Oral contrast: Dense barium → spuriously increased uptake → negative oral contrast (water) should be preferred

Misregistration: Respiratory motion → most pronounced at the level of the diaphragm → banana artefact (curved cold area at the liver dome)

Truncation: Obese patient / arms at the sides → extending beyond the FOV → spuriously increased uptake at the edges

Gold-standard verification for all CTAC artefacts: review of the NAC (non-attenuation-corrected) images

Random coincidence: Proportional to the square of activity (R = 2τ·S₁·S₂)

True coincidence: Directly proportional to activity

Scatter coincidence: Directly proportional to activity; markedly increased in 3D mode (30-50% vs 15-20% in 2D)

Dead time: Loss of counts at high activity → paradoxical fall in counts in the paralyzable model

Parallax error (DOI): Loss of resolution at the edge of the FOV → radial elongation

The most important patient factor affecting SUV: Blood glucose → hyperglycaemia → tumour SUV↓

Upper limit of blood glucose before PET: 150-200 mg/dL

Star artefact: Star-shaped streaks around an intense source in FBP → solution: iterative reconstruction (OSEM)

Ring artefact: Non-uniformity → solution: daily flood QC, PMT calibration

Body contouring orbit: Superior to a circular orbit → detector close to the patient at every angle → resolution↑

Angular sampling: Too few projections → streak artefacts

1. Suspected CTAC artefact → review the NAC images 2. Attenuation artefact vs true defect (cardiac) → CTAC + prone position + gated analysis 3. Suspected misregistration → emission–CT fusion check 4. Suspected ring artefact → flood (uniformity) quality control 5. Suspected COR error → point source COR test 6. Suspected BAT uptake → check for fat density on CT + symmetric pattern

Effective dose cannot be measured → H*(10) (ambient), H_p(10) (whole body), H_p(0.07) (skin), H_p(3) (eye lens)

Controlled area vs supervised area

Category A: likely to receive >6 mSv/year effective, >15 mSv/year eye lens, >150 mSv/year skin/extremity; Category B: those who may exceed the public limit

Absorbed dose: Gray (Gy) = 100 rad → a physical quantity, does not take radiation type into account

Equivalent dose: Sievert (Sv) = 100 rem → corrected with the radiation weighting factor (wR)

Effective dose: Sievert (Sv) → corrected with the tissue weighting factor (wT) → indicator of stochastic risk

For photons and beta wR = 1 → absorbed dose (Gy) = equivalent dose (Sv) numerically

For alpha wR = 20 → 1 Gy of alpha = 20 Sv equivalent dose

Exposure (roentgen) is valid only for photons and in air

In air 1 R ≈ 0.87 rad; in bone the f factor (rad/R) rises markedly at low photon energies (photoelectric, Z³)

Effective dose per MBq: Tl-201 (~0.14-0.22) and Ga-67 (~0.10 mSv/MBq) are much higher than most Tc-99m agents (~0.005-0.01)

Highest wT (0.12): Bone marrow, colon, lung, stomach, breast, remainder tissues

Gonad wT: 0.20 in ICRP 60 → 0.08 in ICRP 103 (reduced)

Breast wT: 0.05 in ICRP 60 → 0.12 in ICRP 103 (raised)

Total wT = 1.00

Dose = Cumulated activity (Ã) × S value

Cumulated activity = area under the activity–time curve = total number of decays

Effective half-life: Teff = (Tphys × Tbiol)/(Tphys + Tbiol) → always shorter than both, closer to the shorter one

S value: A physical parameter depending on radionuclide emissions, organ geometry and mass

Occupational: 20 mSv/year (5-year average; ≤50 mSv in a single year)

Public: 1 mSv/year

Eye lens (ICRP 118): 20 mSv/year average (old: 150 mSv/year)

Skin/extremity: 500 mSv/year

Fetal: 1 mSv (ICRP) or 5 mSv (NRC) for the whole pregnancy

Dose limits do not apply to patients → managed by justification and optimisation

TLD material: LiF (tissue-equivalent)

OSL material: Al₂O₃:C → can be read multiple times (information is not erased)

Film badge: No instant reading, sensitive to heat/humidity

Instant reading: Pocket ionisation chamber or electronic personal dosimeter (EPD)

Lead apron + single dosimeter → outside the apron, at collar level

Gold standard in biological dosimetry: Dicentric chromosome analysis

Dicentrics/rings are unstable (lost with division); past exposure → FISH analysis of stable translocations

ALARA: As Low As Reasonably Achievable

The protection triad: Time, Distance, Shielding

Inverse square law: Distance 2× → dose decreases 4×

Beta shielding: Low Z (Perspex) → to prevent bremsstrahlung

Shielding for P-32 → Perspex (NOT lead)

PET (511 keV) syringe shields → tungsten (high density)

Radioiodine solution is volatile: acidic pH/oxidation increase volatility → alkaline pH + reducing agent, fume hood

White-I: Surface ≤0.005 mSv/h, TI = 0

Yellow-II: Surface ≤0.5 mSv/h, 1 m ≤0.01 mSv/h, TI ≤1.0

Yellow-III: Surface ≤2 mSv/h, 1 m ≤0.1 mSv/h, TI ≤10.0

Radiation Area: 0.05 mSv/h @ 30 cm

High Radiation Area: 1 mSv/h @ 30 cm

Very High Radiation Area: 5 Gy/h @ 1 m

Removable contamination: ≤200 (I-131) / ≤2000 (Tc-99m) dpm/100 cm²

Skin decontamination: Warm water + soap, DO NOT scrub hard

Surface decontamination: Wipe from the outside inwards

Major spill: Leave the area → report to the RSO

I-131 → KI (potassium iodide)

Cs-137 → Prussian blue

Plutonium/Americium → DTPA

Tritium → Plenty of water (forced diuresis)

I-131 is absolutely contraindicated in pregnancy → fetal thyroid damage (from week 10-12 onwards)

Termination of pregnancy is not recommended below 50 mGy

Breastfeeding must be stopped permanently after I-131

Tc-99m compounds: Most require no interruption; 12 hours for pertechnetate and MAA

Ga-67: ≥3-4 weeks (stopped in practice), Tl-201: 48 hours

Activity-based: ≤33 mCi (1.22 GBq)

Dose-rate-based: ≤7 mR/h @ 1 m

Patient-specific: Dose to others ≤5 mSv (child/pregnant woman: ≤1 mSv ICRP/IAEA constraint)

Deviation of more than ±20% in a therapeutic dose

Wrong patient, wrong radiopharmaceutical, wrong route of administration

Reporting: to the NRC by the next calendar day, written report within 15 days

The patient should be informed within 24 hours

The correct term is "radionuclide"; notation ¹⁸F, [¹⁸F]FDG

Half-life ↔ biological process: minutes (O-15, Rb-82), hours (F-18, Ga-68, Tc-99m), days (Zr-89, In-111)

Therapy: decay type, energy, half-life, LET and the whole decay chain (Ac-225 → 4 α)

Primary precursors that can be used directly as agents: [¹⁸F]fluoride, [⁹⁹ᵐTc]pertechnetate

Purification: HPLC/SPE; sterilisation: 0.22 µm filter and/or autoclave

Reactor products → neutron-rich → beta-minus (β⁻) decay

Cyclotron products → proton-rich → positron (β⁺) or electron capture (EC) decay

Fission → high specific activity (carrier-free)

(n,γ) reaction → low specific activity (target and product the same element → chemical separation not possible)

(n,p) reaction → high specific activity (target and product different elements → chemical separation possible)

Primary production of Mo-99: U-235 fission (reactor) → fission yield ~6.1%

HEU → LEU conversion: International pressure because of the risk of nuclear weapons proliferation

F-18: ¹⁸O(p,n)¹⁸F → O-18-enriched water target → T½ = 109.8 min

C-11: ¹⁴N(p,α)¹¹C → N₂ gas target → T½ = 20.4 min

N-13: ¹⁶O(p,α)¹³N → water target → T½ = 9.97 min

O-15: ¹⁵N(p,n)¹⁵O or ¹⁴N(d,n)¹⁵O → T½ = 2.04 min → on-site cyclotron essential

F-18 has the lowest positron energy (Emax = 0.634 MeV) → best PET spatial resolution

Rb-82 has the highest positron energy (Emax = 3.35 MeV) → worst PET spatial resolution

Kryptofix 222 in FDG synthesis → phase-transfer catalyst → toxic → must be tested in quality control

Dry conditions are needed in FDG synthesis → water inhibits nucleophilic substitution

FDG radiochemical purity limit: ≥95%

Mo-99/Tc-99m: Transient equilibrium | Elution with saline | Al₂O₃ column | Lifetime: ~1-2 weeks | Tc-99m elutes as pertechnetate (TcO₄⁻)

Ge-68/Ga-68: Secular equilibrium | Elution with 0.1 M HCl | TiO₂ or SnO₂ column | Lifetime: ~9-12 months

Sr-82/Rb-82: Secular equilibrium | Elution with saline | SnO₂ column | Lifetime: ~4-8 weeks | Automated infusion system needed (T½ = 75 s)

Transient equilibrium: T½(parent)/T½(daughter) ratio relatively small (~10-100) → daughter activity temporarily exceeds parent activity

Secular equilibrium: T½(parent)/T½(daughter) ratio very large (>100) → daughter activity becomes equal to parent activity

Mo-99 breakthrough limit: ≤0.15 µCi Mo-99/mCi Tc-99m → measured by the lead pot method

As the eluate stands the Mo-99/Tc-99m ratio rises (Mo-99 decays more slowly) → the breakthrough limit must also be met at the time of administration

Al breakthrough limit: ≤10 µg Al/mL → measured by a colorimetric test (aurintricarboxylic acid)

High Al → flocculation (large particles) in Tc-99m sulphur colloid → lung uptake; liver uptake with MDP

If the generator is not eluted for a long time → Tc-99 builds up → specific activity falls → labelling efficiency decreases

Maximum Tc-99m build-up after elution: ~23 hours (~4 × T½)

Tc-99m/Mo-99 activity ratio in transient equilibrium: theoretical ~1.10; with branching (87.5%) in practice ~0.96 (does not exceed)

Sr-82 breakthrough limit: ≤0.02 µCi Sr-82/mCi Rb-82

Sr-85 contamination limit: ≤0.2 µCi Sr-85/mCi Rb-82

Sr-82 breakthrough → increases bone dose (strontium is a calcium analogue → accumulates in bone)

Daily quality control is mandatory

Ge-68 breakthrough limit: ≤0.001% Ge-68/Ga-68

Measurement: Wait 48 hours after elution → Ga-68 decays → the remaining activity is Ge-68

Ga-68 can also be produced in a cyclotron by ⁶⁸Zn(p,n)⁶⁸Ga → no risk of Ge-68 breakthrough

Metal contamination (Fe, Cu, Zn) → lowers peptide labelling efficiency → purification with a cation-exchange cartridge

Y-90 and P-32 → cannot be imaged directly (only indirectly via bremsstrahlung)

Y-90: T½ = 2.67 days, Emax = 2.28 MeV → microspheres (radioembolisation), Zevalin

P-32: T½ = 14.3 days, Emax = 1.71 MeV → polycythaemia vera

Alpha emitter (FDA-approved): Ra-223 (Xofigo®) → bone metastases (mCRPC)

Theranostic agents: Lu-177 → both beta (therapy) and gamma (113, 208 keV → SPECT imaging)

I-131 → both beta (therapy) and gamma (364 keV → scintigraphy)

Definition: Radioactivity per unit mass

High specific activity → fission, (n,p), cyclotron production

Low specific activity → (n,γ) reaction

In receptor-based imaging, low specific activity → cold molecules block the receptors → target/background ratio falls

Mo-99 produced by (n,γ) is not ideal for a generator → low specific activity → not enough Mo-99 can be loaded onto the alumina column

Dilution lowers the radioactive concentration (mCi/mL) but does not change specific activity

I-123: The Te-124(p,2n) route contains I-124 impurity; the Xe-124 → Xe-123 → I-123 route gives high purity free of I-124

Mo-99, I-131, Xe-133, Cr-51, P-32, Sr-89, Sm-153, Lu-177, Y-90, Re-186, Er-169, Ho-166

F-18, C-11, N-13, O-15, Ga-67, I-123, In-111, Tl-201, Cu-64, Zr-89

"Reactor = Neutron = Neutron-rich = Beta-minus"

"Cyclotron = Proton = Proton-rich = Positron/EC"

"Same element = No separation = Low specific activity" → (n,γ)

"Different element = Separation possible = High specific activity" → fission, (n,p), cyclotron

Generator elution mnemonic: "Mo-Tc SALINE, Ge-Ga HCL, Sr-Rb SALINE"

Generator equilibrium mnemonic: "Mo-Tc TRANSIENT, Ge-Ga SECULAR, Sr-Rb SECULAR"

Generator column mnemonic: "Mo-Tc ALumina, Ge-Ga TItanium, Sr-Rb TIN"

<40 kDa → capillary extravasation; ≤60 kDa → glomerular filtration; IgG → long blood half-life via FcRn

EPR → non-specific accumulation of large molecules in tumour

DRL → recommended typical diagnostic activity in a standard patient

GLP (non-clinical) vs GMP (production); if terminal sterilisation is not possible, aseptic production + 0.22 µm filtration

Sterility testing is mostly retrospective; Heads of Production and QC are independent; the Qualified Person releases the batch

Reducing agent in Tc-99m kits = stannous chloride (SnCl₂) → reduces pertechnetate from +7 to a lower oxidation state → forms a complex with ligands

Excess SnCl₂ → colloidal Tc formation; insufficient SnCl₂ → free pertechnetate remains

Tc-99m MIBI and MAG3 kits require boiling; other kits are usually prepared at room temperature

Presence of oxygen → SnCl₂ oxidation → labelling efficiency falls → kits are stored under nitrogen

Tc-99m sulphur colloid: Tc is not reduced → precipitates as Tc₂S₇ (+7)

Transchelation intermediate ligands: tetrofosmin (gluconate), MAG3 (tartrate), MIBI (citrate)

MAG3 kit: ~2 mL filtered air into the vial (excess Sn²⁺ is oxidised) + 10 min boiling water bath (benzoyl group is cleaved)

HMPAO: eluate must be ≤2 hours old and the generator eluted within the last 24 hours (Tc-99 build-up impairs labelling); without stabiliser use within 30 min

Capillary blockade: Tc-99m MAA (pulmonary arterioles, 10-100 µm)

Phagocytosis (RES): Tc-99m sulphur colloid (hepatic Kupffer cells)

Active transport: Tl-201 (Na⁺/K⁺-ATPase), I-131/I-123 (NIS); FDG enters by GLUT-facilitated diffusion (metabolic trapping)

Mitochondrial membrane potential: Tc-99m MIBI, Tc-99m tetrofosmin

Chemisorption: Tc-99m MDP/HDP, F-18 NaF (bone surface)

Metabolic trapping: FDG (hexokinase), Tc-99m HMPAO (glutathione → conversion to hydrophilic form)

Compartmental distribution: Tc-99m DTPA (GFR), Tc-99m labelled red cells (blood pool)

Receptor binding: DOTATATE (SSTR2), PSMA, MIBG (uptake-1/NET), OctreoScan (SSTR2)

Tubular secretion: Tc-99m MAG3 (98% tubular secretion)

Tubular binding (cortical fixation): Tc-99m DMSA (proximal tubule)

In vivo: 75-80% (lowest, most free pertechnetate)

In vitro (UltraTag®): >95% (gold standard → preferred for MUGA and GI bleeding)

Metabolic trapping: GLUT → hexokinase → FDG-6-phosphate (low glucose-6-phosphatase → trapping)

Patient preparation: 4-6 hours fasting, blood glucose <150-200 mg/dL, ≥4 hours after insulin

Insulin-sensitive GLUT-4 in myocardium/skeletal muscle → the fed state/insulin increases muscle and myocardial uptake, leaving less FDG for the tumour

False-negative tumours: Lepidic adenocarcinoma, RCC, HCC, prostate Ca, low-grade lymphoma, well-differentiated NET, mucinous tumours

False positives: Infection/inflammation, sarcoidosis, granulomatous disease, brown fat, muscle activity, postoperative changes

Reducing brown fat uptake: Warm environment, propranolol (20 mg orally, 1 hour before), diazepam

Ga-68 DOTATATE (diagnosis) → Lu-177 DOTATATE (therapy/PRRT) → NET

Ga-68/F-18 PSMA (diagnosis) → Lu-177 PSMA (therapy) → mCRPC

Theranostics = diagnostic + therapeutic pair using the same molecular target

I-131: β⁻ + gamma, T½ = 8 days → thyroid cancer, hyperthyroidism

Lu-177: β⁻ + gamma, T½ = 6.65 days → PRRT (DOTATATE), PSMA therapy

Y-90: Pure β⁻ (no gamma), T½ = 64.1 hours → radioembolisation, radioimmunotherapy (Zevalin)

Ra-223: Alpha, T½ = 11.4 days → mCRPC with bone metastases (survival benefit!)

Sr-89: Almost pure β⁻, T½ = 50.5 days → bone pain palliation (long T½ → more toxicity)

Sm-153: β⁻ + gamma, T½ = 46.3 hours → bone pain palliation (short T½ → less toxicity)

Only Ra-223 has shown a survival benefit (ALSYMPCA trial)

Sr-89 and Sm-153 → palliative only, no survival benefit

Ra-223 → alpha emitter (high LET, short range 100 µm)

Ra-223 → indicated only in mCRPC with bone metastases (visceral metastases → contraindicated)

Pre-treatment Tc-99m MAA shunt study is mandatory

Lung shunt >20% → contraindicated

Lung shunt 10-20% → dose reduction

GI shunt → prophylactic coil embolisation

TheraSphere® (glass) vs SIR-Spheres® (resin) → resin has a greater embolic effect

RAI: Amiodarone → 3-6 months (longest); levothyroxine → 3-4 weeks; methimazole → 2-5 days

MIBG: Antipsychotics → ~3-4 weeks (longest); labetalol → 10 days; TCA → 1-3 days

FDG PET: G-CSF → 2-4 weeks; chemotherapy → 2-3 weeks; radiotherapy → 2-3 months

Mo-99 breakthrough: ≤0.15 µCi Mo-99/mCi Tc-99m → lead container + dose calibrator

Al³⁺ breakthrough: ≤10 µg/mL → colorimetric test

Radiochemical purity (RCP): ≥90% for most Tc-99m kits → measured by TLC

TLC + acetone → measures free pertechnetate (migrates with the front)

TLC + saline → measures colloidal Tc (stays at the origin)

RCP = 100 - free TcO₄⁻ (%) - colloidal Tc (%)

Large joint (knee): Y-90 (penetration 11 mm)

Medium joint (shoulder, hip): Re-186 (penetration 3.6 mm)

Small joint (finger): Er-169 (penetration 1 mm)

Teff = (Tphys × Tbiol) / (Tphys + Tbiol)

Always shorter than both the physical and the biological half-life

The effective half-life is used in dose calculations (MIRD)

<10 nm → blood capillaries (10-100 nm → lymph nodes)

10-100 nm → sentinel lymph node (filtered sulphur colloid)

100-1000 nm → RES phagocytosis (sulphur colloid)

10-100 µm → capillary blockade (MAA)

20-60 µm → microsphere embolisation (Y-90 SIR-Spheres)

Pertechnetate → trapping only (entry via NIS, no organification)

Iodine (I-123, I-131) → trapping + organification

Discordant nodule: hot on Tc-99m, cold on iodine → malignancy risk → biopsy

NETTER-1 trial → PFS benefit

Dose: 7.4 GBq × 4 cycles (8 weeks apart)

Renal protection: Amino acid infusion (lysine + arginine) → reduces tubular reabsorption

Dose-limiting organs: Kidneys and bone marrow

VISION trial → OS and PFS benefit

Dose: 7.4 GBq × 6 cycles (6 weeks apart)

Patient selection: Positivity must be confirmed by PSMA PET

Dose-limiting: Salivary glands (xerostomia), kidneys, bone marrow

1. NIS location: Basolateral membrane. NIS is expressed not only in the thyroid but also in the salivary glands, gastric mucosa, lactating breast and choroid plexus.

2. Pertechnetate vs iodine: Pertechnetate → trapping only (no organification). Iodine (I-123, I-131) → trapping + organification. Discordant nodule: hot on pertechnetate, cold on iodine → FNAB required.

3. Normal thyroid uptake values: 24 hours → 10-30%. 4. Hyperthyroidism + low uptake: Thyroiditis (subacute, silent, postpartum), exogenous hormone, iodine loading, struma ovarii.

5. Hyperthyroidism + high uptake: Graves (diffuse homogeneous), toxic MNG (heterogeneous), toxic adenoma (focal + suppressed surroundings).

6. Cold nodule: Malignancy risk 5-15% → FNAB indicated. 85-95% of cold nodules are benign. 7. Wolff-Chaikoff: High iodine → inhibition of organification → hypothyroidism (protective). Jod-Basedow: high iodine → hyperthyroidism in autonomous tissue (pathological).

8. Before RAI therapy: TSH target >30 mIU/L (hormone withdrawal or rhTSH), low-iodine diet for 1-2 weeks, mandatory pregnancy test, iodine-containing drugs stopped.

9. Stunning: Diagnostic I-131 → NIS expression falls → treatment efficacy falls. Prevention: use I-123, low-dose I-131 (≤3 mCi), give therapy within ≤72 hours.

10. Differentiated thyroid cancer: Papillary (80-85%) and follicular (10-15%) → RAI-avid. Medullary → not RAI-avid (C cell, no NIS). Anaplastic → not RAI-avid (dedifferentiated).

11. Post-therapy WBS: More sensitive than diagnostic WBS → additional lesions in 10-26% of patients. 12. Dosimetric therapy limits: Bone marrow ≤200 cGy, lung retention <80 mCi at 48 hours. 13. Thyroglobulin (Tg): Tumour marker after total thyroidectomy + RAI. Anti-Tg antibodies interfere with Tg measurement.

Anti-Tg antibodies cause falsely low values in immunometric (IMA) Tg assays → Tg is always measured together with anti-Tg.

Thyrotoxicosis + low uptake: serum Tg is suppressed in thyrotoxicosis factitia and high in thyroiditis.

Perchlorate discharge test (I-123): >10% fall in uptake after perchlorate → organification defect (Pendred, TPO defect, Hashimoto).

~25% of MTC is hereditary (germline RET) → RET testing in every MTC; MEN2A: MTC + phaeo + HPT, MEN2B: MTC + phaeo + marfanoid habitus + mucosal neuromas (no HPT).

14. Causes of PHPT: Single adenoma 80-85%, hyperplasia 10-15%, carcinoma 1-2%, double adenoma 2-5%. 15. Mechanism of MIBI retention: Lipophilic cationic complex → mitochondrial membrane potential. Oxyphil cells → rich in mitochondria → intense MIBI uptake.

16. Dual-phase principle: Slow washout in parathyroid adenoma → retention in the delayed phase. False negative: adenoma with rapid washout.

17. Subtraction technique: MIBI − pertechnetate (or I-123) = parathyroid. Superior to dual-phase in adenomas with rapid washout.

18. Ectopic parathyroid: Most commonly intrathymic. Inferior glands → 3rd pharyngeal pouch → migrate with the thymus. Superior glands → 4th pharyngeal pouch → more constant.

19. SPECT/CT: Superior to planar imaging → anatomical localisation + detection of ectopic glands. Many guidelines recommend routine SPECT/CT.

20. NP-59: Cholesterol analogue → adrenal cortex. Unilateral early uptake under dexamethasone → autonomous adenoma; absent bilateral uptake under dexamethasone is normal. No bilateral uptake in a non-suppressed study → suggests carcinoma (dedifferentiated). Its use has declined.

21. MIBG: Norepinephrine analogue → taken up by uptake-1 (NET). Thyroid blockade mandatory. Longest withdrawal: antipsychotics (~3-4 weeks; depot ~1 month). Physiological uptake: liver (most intense), heart, salivary glands, adrenal, bladder.

22. Phaeochromocytoma: 10% rule (currently: hereditary proportion up to 30-40%). MIBG sensitivity 85-95%. In paraganglioma Ga-68 DOTATATE > MIBG.

23. Neuroblastoma: The commonest extracranial solid tumour of childhood. MIBG sensitivity 88-93%. Curie score: semi-quantitative MIBG assessment. 8-10% MIBG-negative → FDG PET/CT.

24. OctreoScan: Binds SSTR2. Most intense physiological uptake: spleen. Low sensitivity in insulinoma. Replaced by Ga-68 DOTATATE.

25. Ga-68 DOTATATE PET/CT: Gold standard for NET staging. Sensitivity 92-97%. PRRT patient selection (Krenning ≥2). Theranostic pair: Ga-68 diagnosis → Lu-177 therapy.

26. Flip-flop phenomenon: Well-differentiated NET → DOTATATE (+), FDG (−). Poorly differentiated NET/NEC → DOTATATE (−), FDG (+).

27. NET grading: Grade 1: Ki-67 <3%. Grade 2: Ki-67 3-20%. Grade 3: Ki-67 >20%. 28. PRRT (Lu-177 DOTATATE): 7.4 GBq × 4 cycles, 8 weeks apart. Renal protection: amino acid infusion. NETTER-1 trial: PFS benefit in midgut NET.

29. Krenning score: Grade 0-4. For PRRT ≥Grade 2 (tumour ≥ liver). Grade 4 = equal to/greater than spleen.

30. Carcinoid syndrome: SSA (octreotide LAR) → symptom control + antiproliferative (PROMID, CLARINET trials).

MIBG sensitivity is ~90% in phaeochromocytoma/neuroblastoma, ~50-70% in carcinoid and ~ 30% in MTC; there is normally no bone/bone marrow uptake → skeletal uptake favours metastasis.

31. Pertechnetate: 74-111 MBq, peak uptake at ~20 min (2-5%), ~1 mSv; perchlorate test not possible. I-123: 7.4-14.8 MBq, normal 2-hour uptake 10-15%, ~1.2 mSv.

32. I-131 diagnostic WBS: 37-74 MBq after hormone withdrawal, 110-148 MBq with rhTSH (SNMMI/EANM 2022); not used diagnostically under 10 years of age except for thyroid cancer. SPECT/CT: remnant vs lymph node, lung vs rib, bowel vs pelvic bone.

33. I-124 PET/CT: 20-74 MBq orally; dosimetry at 4-24-48-72-96 hours; target dose ~300 Gy for remnant, 80-100 Gy for metastases.

34. Thyroid MIBI: Independent of TSH/NIS, requires viable cells. AIT-1 normal/increased, AIT-2 reduced/absent, AIT-3 mixed. Indeterminate nodule (>1 cm, EU-TIRADS 4-5, Bethesda III/IV): MIBI-negative → high NPV; WOind threshold −19%.

35. Parathyroid MIBI: 400-900 MBq; early 10-15 min, delayed 1.5-2.5 hours; MIBI SPECT/CT detection rate ~88%; main pitfall an MIBI-avid thyroid nodule.

36. Parathyroid PET: F-18 fluorocholine (choline kinase) → sensitivity 94%, PPV 97%, cure 93%; first choice in MEN, renal HPT, persistent/recurrent and normocalcaemic HPT. C-11 methionine (LAT1/2) less sensitive. Success in renal HPT = >50% fall in PTH.

37. NP-59 (EANM): 20 MBq, ~36 mSv/procedure; thyroid blockade mandatory; dexamethasone 4 mg/day from 1 week before; spironolactone stopped ≥6 weeks before; imaging on days 5 and 8.

38. MIBG (EANM): I-123 185-370 MBq (13 µSv/MBq), I-131 40-80 MBq (140 µSv/MBq); critical organ liver. Thyroid blockade for 2-3 days with I-123 and 5-10 days with I-131.

39. SSTR imaging: Tc-99m HYNIC-TOC (Tektrotyd®) first choice among gamma agents; In-111 pentetreotide ~12 mSv. DOTANOC has the broadest affinity (SSTR2/3/5); SUV values of different SSTR PET agents cannot be compared; critical organ for Ga-68 DOTATATE is the spleen.

40. Benign insulinoma: High GLP-1R, low SSTR2 → Ga-68 exendin-4 PET/CT (accuracy 94.4%); false positives nesidioblastosis, Brunner glands.

Tl-201: Na⁺/K⁺-ATPase, first-pass extraction 85%, redistribution present, T½ = 73 hours, low energy (69-83 keV)

Tc-99m MIBI: Mitochondrial membrane potential, first-pass extraction 60-65%, no redistribution, marked hepatic excretion

Tc-99m Tetrofosmin: Mitochondria, first-pass extraction 54%, faster hepatic clearance than MIBI, labelling at room temperature

Ranking (first-pass extraction): Tl-201 > N-13 ammonia > Rb-82 > MIBI > Tetrofosmin

Exercise is always preferred → target heart rate: (220 − age) × 0.85

Vasodilators: Adenosine (direct A2A, T½ 10 s), dipyridamole (indirect), regadenoson (selective A2A, bolus, most widely used)

For all vasodilators: Caffeine stopped 12-24 hours before (theophylline 48 hours); antidote = aminophylline

Asthma/COPD → vasodilators contraindicated → dobutamine (antidote: esmolol)

LBBB → vasodilator preferred (exercise/dobutamine → false septal defect)

Diaphragmatic attenuation: Male, inferior, fixed defect, normal wall motion → prone imaging

Breast attenuation: Female, anterior/anterolateral, fixed defect, normal wall motion

Gated SPECT: Attenuation artefact vs true defect → normal motion = artefact

TID: Severe multivessel / left main disease → high risk

Increased lung uptake (Tl-201): Severe LV dysfunction → high risk

Balanced 3-vessel disease: Normal-looking MPI → MBF/CFR measurement with PET

Reverse redistribution (defect becoming more conspicuous on the delayed image): Mostly reperfused infarction, not ischaemia

The LBBB false defect is confined to the septum and spares the apex; extension to the apex/anterior wall indicates true LAD ischaemia

Hibernation: Perfusion ↓ + FDG ↑ (mismatch) → benefits from revascularisation

Stunning: Normal perfusion + transiently impaired function → recovers spontaneously

Scar: Perfusion ↓ + FDG ↓ (match) → irreversible

FDG PET mismatch → gold standard for viability

Tl-201 reinjection: 40-50% of fixed defects show fill-in

Allman meta-analysis: In viable myocardium revascularisation reduces annual mortality from 16% to 3.2%; no difference without viable myocardium

Viability preparation: Glucose loading (the exact opposite of sarcoidosis preparation!)

The most reproducible method of LVEF measurement

Doxorubicin monitoring: Fall ≥10% + LVEF <50% → stop chemotherapy

If baseline LVEF <50%: fall ≥10% or LVEF ≤30% → stop; baseline ≤30% → do not start

Phase analysis: Dyskinesia/aneurysm ~180° opposite phase to the ventricle; WPW pre-excitation site early phase

Red cell labelling: In vitro >97% (best), in vivo 75-80% (lowest)

AF → gating degraded → reduced accuracy

Delayed H/M ≥1.6 → low risk → good prognosis (normal ≥~1.8-2.0)

Delayed H/M <1.6 → sympathetic denervation → poor prognosis, high arrhythmic risk

DLB → MIBG reduced; Alzheimer → MIBG normal

Parkinson → MIBG reduced (postganglionic); MSA → MIBG preserved (preganglionic)

Detects ATTR amyloidosis (AL not detected)

Perugini Grade 2-3 + negative monoclonal protein → ATTR diagnosis without biopsy

SPECT/CT → mandatory to exclude blood pool activity

Patient preparation: ≥12-18 hours fasting + high-fat/low-carbohydrate (suppress physiological uptake)

Focal/focal-on-diffuse FDG → pathological; diffuse homogeneous → inadequate preparation

Normal perfusion + focal FDG ↑ → early active inflammation

Used to monitor treatment response

Rb-82: Generator, T½ = 75 s, Na⁺/K⁺-ATPase, vasodilator stress mandatory, daily Sr-82 breakthrough test

N-13 ammonia: Cyclotron, T½ = 10 min, glutamine synthetase, exercise stress possible, best resolution

O-15 water: Cyclotron, T½ = 2 min, free diffusion, first-pass extraction 100%, gold standard for MBF, rare in clinical practice

CFR = Stress MBF / Rest MBF → normal ≥2.0 → <2.0 abnormal → <1.5 severely abnormal

Balanced 3-vessel disease → detected by MBF/CFR

SSS: Total stress score; SRS: total rest score; SDS = SSS − SRS (amount of ischaemia)

Normal MPI → annual cardiac event risk <1% (warranty period ~2 years)

Ischaemic myocardium ≥10% → revascularisation should be considered

17-segment model (AHA): LAD → anterior + anteroseptal + apex (largest territory)

Tl-201: ~4% reaches the myocardium; extraction preserved in acidosis/hypoxia, reduced in fibrosis; plateau at 2-2.5 × resting flow; 74-111 MBq (+37 MBq reinjection); breastfeeding interrupted for 48 hours

Tc-99m agents: Plateau at ~2 × resting flow; 1-day protocol stress 250-400 MBq + 3 times that for rest ≥3 hours later; breastfeeding not interrupted

Withdrawal: β-blocker/Ca antagonist/nitrate 48 hours, dipyridamole 72 hours, theophylline 48 hours, caffeine ≥12 (preferably 24) hours

Rate-pressure product >25,000 adequate, >30,000 excellent; target heart rate >85%

Normal MPI annual MACE ~1% (women ~0.3%, pharmacological stress ~2%); post-stress stunning: EF fall lasting >60 min

Reverse mismatch: LBBB, early revascularised MI, non-ischaemic CMP, diabetes → considered viable

FPRNA: Shunt (Qp/Qs), RV function, cardiac output; 555-1110 MBq

Cardiac MIBG: 15 min and 4 hours, LEHR; ADMIRE-HF 2-year events 15% (H/M ≥1.6) vs 37%; 80-90% reduction in Lewy body diseases; PD/DLB threshold ~1.77

Amyloidosis: score ≥2 at 3 hours + AL excluded → ATTR; marked uptake may occur in >20% of AL

Cardiac sarcoidosis: 24-hour high-fat/low-carbohydrate diet; CAD should be excluded by perfusion

Agent: Tc-99m MDP/HDP → chemisorption to hydroxyapatite

Most important determinant of uptake: Osteoblastic activity

Dose: 20-25 mCi, imaging 2-4 hours later

High sensitivity (~95%), low specificity

Critical organ: Bladder (renal excretion)

Commonest indication: Screening for bone metastases

Phase 1: Perfusion (flow) → arterial blood flow

Phase 2: Blood pool → soft tissue hyperaemia

Phase 3: Delayed (bone) → osteoblastic activity

Osteomyelitis: Focally increased in all three phases

Cellulitis: Phases 1-2 diffusely increased, phase 3 normal

Low specificity in the diabetic foot → labelled leucocytes + bone marrow preferred

Acute osteomyelitis: Bone scintigraphy positive at 24-72 hours, radiography only at 10-14 days; a continued rise in the lesion/bone ratio at 24 hours favours osteomyelitis

Mechanism: Exchange with OH⁻ → fluorapatite

Compared with Tc-99m MDP: Higher sensitivity, better resolution, faster (45-60 min)

Disadvantage: Cost, access

Metastatic: Asymmetric, heterogeneous → prostate, breast cancer

Metabolic: Symmetric, homogeneous → HPT, renal osteodystrophy, osteomalacia

Common feature: Kidneys not visualised

"Beautiful bone scan" → may be a superscan → check the kidneys!

Multiple myeloma (board classic → purely osteolytic)

Renal cell carcinoma, anaplastic thyroid cancer

Early AVN, after radiotherapy, metal prosthesis

In myeloma → use FDG PET/CT or low-dose whole-body CT

Free pertechnetate → thyroid, stomach, salivary glands (labelling failure)

Metastatic calcification → lung, stomach, kidney (hypercalcaemia)

Dystrophic calcification → MI, rhabdomyolysis, myositis ossificans

H (Honda) sign: Sacral insufficiency fracture

Doughnut pattern: AVN (late phase)

Expanded bone + intense uptake: Paget disease

Periarticular increased uptake: CRPS (RSD)

Rosary bead: Osteomalacia (costochondral junctions)

Double density sign: Osteoid osteoma (intense nidus + surrounding reactive uptake)

Bilateral symmetric linear periosteal uptake along long bone cortices ("tram-track"): hypertrophic pulmonary osteoarthropathy (bronchogenic carcinoma)

Early phase: Cold lesion (blood flow interrupted)

Late phase: Increased uptake or doughnut pattern (reparative)

Gold standard: MRI

Commonest location: Femoral head

Normal postoperative uptake: Uncemented → 2 years, cemented → 6-12 months

Loosening vs infection → bone scintigraphy alone cannot distinguish them

Gold standard: Labelled leucocyte + bone marrow scintigraphy

Incongruent pattern → infection; congruent → no infection

Paradoxical worsening 2-3 months after treatment

Sign of good prognosis (response to treatment)

Improvement at 6 months → flare; continued worsening → progression

Positive 2-4 weeks before radiography

Spondylolysis → evaluate with SPECT/CT

Bone scintigraphy after trauma: positive 24-72 hours later (may be delayed in the elderly)

MRI → positive immediately → preferred for urgent evaluation

Shin splints: Longitudinal superficial uptake along the posteromedial tibial cortex, only the delayed phase positive (in stress fracture: focal fusiform, all three phases positive)

Bone scintigraphy + radiography → complementary

Bone scintigraphy → better for rib fractures; classic metaphyseal lesion and skull fracture → radiography better

Radiography → better for skull fractures

Most frequently involved bone: Pelvis

Complication: Osteosarcoma (less than 1%)

Bone scintigraphy → assessment of disease extent and activity

Treatment response: Reduced uptake after bisphosphonates

A photopenic area or intense FDG uptake in Paget disease → think of sarcomatous transformation

Vertebral body → high probability of metastasis

Facet joint / posterior elements → high probability of degenerative change

Disc space + both adjacent vertebrae → discitis-osteomyelitis

Bisphosphonate kinetics: at 4 hours ~60% skeleton, ~34% urine, ~6% circulation; maximal bone accumulation at 1 hour; adult 300-740 MBq, 4.9 µSv/MBq (3-4 mSv)

Soft tissue ↑: Renal failure, dehydration, failed labelling, short wait; ↓: superscan, very long wait; commonest artefact: urinary contamination

NaF: 50% in bone, ~30% in red cells; 185-370 MBq, 17 µSv/MBq, critical organ bladder; axial 30-45 min, extremities 90-120 min; valuable in ESRD and morbid obesity

DXA: T ≤ −2.5 osteoporosis, −1.1/−2.4 low bone mass; premenopausal/men <50 → Z score (≤ −2.0); forearm → non-dominant radius 33%; patient dose 1-10 µSv

Tc-99m MAG3: Tubular secretion (~95-98%; protein binding ~90%), extraction fraction ~40-50%, measures ERPF, preferred agent

Tc-99m DTPA: Glomerular filtration, extraction fraction ~20%, measures GFR

Tc-99m DMSA: Cortical retention, static imaging, pyelonephritis/scar, differential function (most accurate)

MAG3 → good images even with low function → general preference

DTPA → when GFR measurement is needed

Phase 1: Vascular (0-30 s) → perfusion

Phase 2: Parenchymal (1-5 min) → uptake → Tmax occurs here → differential function is calculated here

Phase 3: Excretion (5+ min) → drainage → T½ is calculated here

Normal Tmax: 3-5 min (MAG3), Normal T½: <10 min

T½ <10 min → non-obstructive

T½ 10-20 min → equivocal

T½ > 20 min → obstructive

Commonest cause of false positives: Dehydration

In a very dilated system: F-15 protocol preferred (reduces the reservoir effect)

Furosemide dose: Adult 40 mg IV, paediatric 1 mg/kg

Commonest level of obstruction: UPJ in children, UVJ in adults (mostly stones)

Sawtooth fluctuation in the drainage phase → VUR during renography (not a sign of obstruction)

Principle: ACE inhibition → efferent arteriolar dilatation → fall in GFR → asymmetry

Most sensitive criterion: Prolonged Tmax

ACE inhibitors should be stopped 3-5 days before the study

False negative in bilateral stenosis (symmetric deterioration → no asymmetry)

Positivity thresholds (MAG3): Prolongation of Tmax by ≥2 min, rise in the 20-min/peak ratio of ≥0.15; with DTPA a fall in relative uptake

Use has declined today → CT/MR angiography more widely used

GFR gold standard: Inulin clearance (physiological), practical: Tc-99m DTPA

ERPF gold standard: PAH clearance, practical: Tc-99m MAG3

Normal GFR: 120 ± 25 mL/min

Normal ERPF: 600 ± 150 mL/min

Filtration fraction: GFR/RPF ≈ 20%

Gates method: Camera-based GFR → fast, gives differential GFR

Imaging: 2-4 hours after injection

Acute pyelonephritis: Focal reduced uptake, NO volume loss

Renal scar: Focal defect + volume loss (cortical thinning)

Most sensitive method for diagnosing acute pyelonephritis in children (with SPECT)

Most accurate method for measuring differential function

Pseudotumour (column of Bertin, dromedary hump) shows normal cortical uptake → distinguished from a true mass

Initial assessment: VCUG (anatomical detail, VUR grade, urethral pathology)

Follow-up: DRNC (low radiation, high sensitivity, continuous dynamic imaging)

Catheter-free method: IRNC (requires a cooperative patient, >3 years, voiding phase only)

DRNC radiation dose: ~1/100 of VCUG

Imaging: Anterior (pelvic location)

Preferred agent: Tc-99m MAG3

ATN vs Acute Rejection → the most important difference: Perfusion

ATN: Perfusion preserved, improvement on serial follow-up

Rejection: Perfusion reduced, deterioration on serial follow-up

Photopenic kidney (no perfusion + no uptake): Hyperacute rejection or renal artery thrombosis

Activity collection outside the bladder: Urine leak (urinoma)

A urinoma is photopenic early and accumulates activity over time; a lymphocele remains photopenic on delayed images too

ATN → common with deceased donors (cold ischaemia)

Chronic rejection → definitive diagnosis: Biopsy

"Which agent with low renal function?" → MAG3

"Which agent for GFR measurement?" → DTPA

"Most sensitive for diagnosing pyelonephritis?" → DMSA SPECT

"Preferred for VUR follow-up?" → DRNC

"Difference between transplant ATN and rejection?" → Perfusion (preserved in ATN)

"Principle of captopril renography?" → Efferent arteriolar dilatation → fall in GFR

"Limitation of captopril renography in bilateral stenosis?" → False negative

"Filtration fraction?" → 20% (GFR/RPF)

First-pass extraction: OIH ~80% > Tc-99m EC ~65% > MAG3 ~55% > DTPA ~20%

EANM activities: MAG3 75 MBq, DTPA 37-185 MBq, DMSA 70 MBq, DRNC 20 MBq

MAG3: 80-90% protein binding, ~10% hepatobiliary; its clearance is not reported as ERPF; probenecid is stopped

Differential function: Rutland-Patlak best; symmetry 50 ± 7.5%; C-shaped perirenal background ROI; µ = 0.14/cm

Cr-51 EDTA: Clearance ratio to inulin 0.85-1.01; ascites/oedema/GFR <30 → EANM: urine collection instead of plasma sampling (BNMS 2018: adapted plasma methods with late/24-hour samples)

DMSA: Acute defect is patchy and follows the contour; scar is triangular and distorts the contour; Fanconi, bicarbonate, mannitol reduce uptake

DRNC: Pertechnetate may be absorbed in an augmented bladder → false positive → use DTPA or colloid

Captopril: Dehydration/sodium depletion cause false positives; at creatinine <1.7 mg/dL sensitivity/specificity ~90%

Particle size: 10-90 μm (mean 20-40 μm)

Standard particle number: 200,000-700,000

Proportion of arterioles occluded: 0.1-0.3% → haemodynamically safe

Injection position: Supine (to reduce the effect of gravity)

Particle number in pulmonary hypertension: reduce to 100,000-150,000

In right-to-left shunt: Reduce particle number (risk of cerebral embolisation)

In pregnancy: Reduce activity (1-2 mCi); the particle number does not go below 100,000

Egg allergy → NOT a contraindication (MAA is made from human albumin)

If blood is drawn into the syringe → clot → "hot spot" artefact

Xe-133: 81 keV, washout phase most important (air trapping), posterior projection only, ventilation must be performed FIRST

Tc-99m DTPA aerosol: 140 keV, 0.5-2 μm, clumping problem in COPD, all projections, most widely used

Technegas: 140 keV, FDA-approved (2023)

Kr-81m: 190 keV, 13 s half-life, simultaneous imaging with Tc-99m, very expensive

Mismatch = perfusion defect + normal ventilation → favours PE

Match = perfusion + ventilation defect in the same area → not PE (COPD, pneumonia)

Reverse mismatch = ventilation defect + normal perfusion → mucus plug, bronchial obstruction

Stripe sign = rim of perfusion at the periphery of a perfusion defect → low probability of PE

Complete loss of perfusion to one lung is rare in PE → central tumour/compression by a hilar mass (if matched on ventilation: central carcinoma, foreign body, Swyer-James)

Reversal of the perfusion gradient (upper zone > lower zone) → pulmonary venous hypertension (left heart failure, mitral stenosis)

High probability: ≥2 large segmental mismatches (probability of PE ~80-90%)

Intermediate: The most problematic category → high non-diagnostic rate

Low probability: Small defects, non-segmental defects, matched defects (probability of PE ~ 10-15%)

Triple match in a lower lobe: Probability of PE ~33% → intermediate

Normal: Probability of PE <5% → PE excluded

Triple match in an upper/middle lobe: Low probability of PE

Clinical probability (Wells score) and the V/Q result should be assessed together

PIOPED II very low probability (<10%): Non-segmental defect, 1-3 small segmental defects, single-segment triple match in the middle/upper zone, stripe sign, large effusion without other defects

V/Q is more sensitive than CTPA for CTEPH screening; a normal V/Q excludes CTEPH

Large: >75% of a segment

Moderate: 25-75% of a segment

Small: <25% of a segment

V/Q preferred: Contrast allergy, renal failure, pregnancy, young woman, normal chest radiograph

CTPA preferred: Abnormal chest radiograph (COPD), alternative diagnosis sought, haemodynamic instability

SPECT → intermediate rate falls from 30-40% to <5% (SNMMI/EANM 2026)

SPECT/CT → attenuation correction + anatomical correlation + alternative diagnosis

ppoFEV1 = Preop FEV1 × (1 − perfusion fraction of the lung to be resected)

ppoFEV1 >40% or >0.8 L → surgery generally safe

ppoFEV1 30-40% → increased risk, further assessment

ppoFEV1 <30% or <0.8 L → high risk, generally contraindicated

Right lung segment number: 10, Left lung: 8-9, Total: 18-19

Right-to-left shunt: With Tc-99m MAA → uptake in systemic organs → normal <5%

Systemic activity after MAA: Brain uptake → right-to-left shunt; thyroid/stomach (no brain) → free pertechnetate

Left-to-right shunt: First-pass radionuclide angiocardiography → Qp/Qs ratio

Qp/Qs = 1.0 → normal

Qp/Qs > 1 → left-to-right shunt

Qp/Qs < 1 → right-to-left shunt

Qp/Qs > 1.5 → haemodynamically significant → consider surgical correction

Pulmonary AVM → Osler-Weber-Rendu syndrome (HHT)

Hepatopulmonary syndrome → cirrhosis + intrapulmonary vascular dilatation

"Preferred test for suspected PE in a pregnant patient?" → V/Q scintigraphy (low breast dose)

"Best ventilation agent in COPD?" → Technegas

"V/Q order with Xe-133?" → Ventilation FIRST (low energy first)

"Agent allowing simultaneous V/Q?" → Kr-81m (190 keV)

"PIOPED high-probability criterion?" → ≥2 large segmental mismatches

"Stripe sign?" → Low probability of PE

"Triple match in a lower lobe?" → Probability of PE ~33% (intermediate)

"ppoFEV1 safety limit?" → >0.8 L or >40%

"Normal right-to-left shunt?" → <5%

"How is a left-to-right shunt assessed?" → First-pass angiocardiography, Qp/Qs

"Can a left-to-right shunt be assessed with MAA?" → NO

MAA: 40-120 MBq, 11 µSv/MBq, breastfeeding 12 hours; <100,000 particles (SNMMI/EANM 2026) or non-supine injection → irregular distribution

EANM PE criterion: ≥1 segment or ≥2 subsegment mismatch; V/Q SPECT ≥95% diagnostic, NPV ≥97%; with CT specificity 88% → 100%

Ventilation doses: Kr-81m lowest (27 nSv/MBq); Technegas 20-30 MBq (15 µSv/MBq); DTPA aerosol 900-1300 MBq in the nebuliser (SNMMI/EANM 2026)

DTPA aerosol clearance: Normal <2%/min; 2-5 times faster in smokers; increased in fibrosis, sarcoidosis, ARDS, PCP

Mucociliary clearance: Normal nasal ~6 mm/min, tracheobronchial ~4 mm/min; ~0.2 mm/min in PCD

Agent: Tc-99m pertechnetate (taken up via NIS)

Stimulation: Lemon juice (at 15-20 minutes)

Sjögren syndrome: Reduced uptake + absent/reduced secretion

Pertechnetate-avid tumour: Warthin tumour (hot nodule)

Commonest salivary gland tumour: Pleomorphic adenoma → does not take up pertechnetate (cold)

Agent: Tc-99m sulphur colloid (in liquid)

Normal transit time: <15 seconds (classical); EANM upper limit ≤30 seconds

Scleroderma: Retention in the lower 2/3 of the oesophagus (smooth muscle involvement)

Achalasia: Retention at the LOS

Agent: Tc-99m sulphur colloid (in acidic liquid/milk)

Lung activity on delayed images → pulmonary aspiration

The preferred non-invasive method in paediatric patients

Gold-standard method

Standard meal: Egg-white sandwich (Tc-99m sulphur colloid)

<30% retention at 1 hour → rapid emptying (dumping)

>10% retention at 4 hours → gastroparesis (Mild 11-20%, Moderate 21-35%, Severe >35%)

Solid food: Linear kinetics (lag phase + linear phase)

Liquid food: Exponential kinetics

Geometric mean: For attenuation correction (square root of anterior × posterior)

Blood glucose in a diabetic patient: ≤275 mg/dL

Drug withdrawal: Prokinetics, opioids, anticholinergics → 48-72 hours before

Truncal vagotomy: Liquids empty rapidly (loss of fundic relaxation), solids are delayed (impaired antral grinding)

Agent: Tc-99m pertechnetate IV → uptake by ectopic gastric mucosa

Rule of twos: 2%, 2 feet, 2 inches, 2 years, 2 types of mucosa, 2:1 M/F

Premedication: Cimetidine (H2 blocker) → blocks secretion → signal increases

Positive finding: Focal activity in the right lower quadrant → appears at the same time as the stomach

Sensitivity in children: 85-95%; in adults: 60-70%

Pancreatic mucosa → does not take up pertechnetate → scintigraphy negative

Agent: Tc-99m labelled red blood cells

Labelling efficiency: In-vivo 75-80%, In-vivtro 85-90%, In-vitro >95%

Detection threshold: 0.1-0.4 mL/min (angiography: 0.5-1.0 mL/min)

Localisation: The first focal activity to appear is the most reliable

Delayed imaging up to 24 hours → advantage in intermittent bleeding

Free pertechnetate → uptake in the stomach, thyroid, kidney → artefact

Gastric activity + thyroid/salivary glands seen → free pertechnetate; not seen → true gastric/upper GI bleeding

Agents: Mebrofenin/BrIDA (most common; preferred in hyperbilirubinaemia), DISIDA (sufficient at bilirubin <5 mg/dL)

Bilirubin >5 mg/dL → mebrofenin; >20 mg/dL → even mebrofenin may be inadequate

Acute cholecystitis: 60 min without gallbladder visualisation → morphine augmentation (0.04 mg/kg IV)

Mechanism of morphine: Contraction of the sphincter of Oddi → biliary pressure rises

Rim sign → gangrenous cholecystitis / perforation → emergency surgery

Morphine is given only after bowel activity (common bile duct patency) has been seen; the main cause of false negatives is acalculous cholecystitis

GBEF: Sincalide (CCK-8) 60 min infusion → normal ≥38%; <38% → dyskinesia

Neonatal jaundice: Phenobarbital 5 mg/kg/day for 5 days → distinguishes biliary atresia from hepatitis

Biliary atresia: NO passage into the bowel at 24 hours (not specific: severe neonatal hepatitis, Alagille, α1-antitrypsin deficiency); Kasai <60 days most successful

Bile leak: Focal accumulation of activity outside the bile ducts

Normal distribution: Liver 85-90%, Spleen 5-10%, Bone marrow 3-5%

Colloid shift → cirrhosis (splenic and bone marrow uptake increased)

FNH → takes up sulphur colloid (contains Kupffer cells)

Adenoma, metastasis, cyst, abscess → do not take up sulphur colloid

Budd-Chiari → increased caudate lobe uptake (direct IVC drainage)

Flow phase: Reduced/normal perfusion

Delayed phase: Increased uptake (more intense than the liver) → fill-in pattern

Sensitivity: >2 cm lesions 90-95%; at 1.5 cm low → MR preferred

Malignant tumour: Increased in the flow phase, reduced in the delayed phase (the exact opposite)

Detects H. pylori urease activity

C-14: Radioactive → contraindicated in pregnancy; C-13: Non-radioactive → safe

PPI withdrawal: 2 weeks; Antibiotic/bismuth withdrawal: 4 weeks

Eradication check: 4 weeks after treatment

Sensitivity and specificity: >95%

Salivary gland: 37 MBq, maximum uptake at ~30 min; increased uptake + reduced secretion in sialadenosis; breastfeeding 12 hours

ETS: Normal transit ≤30 s; sensitivity 95%, specificity 96% in achalasia/scleroderma; manometry is the gold standard

GOR: First-line pH-metry/impedance; valuable for airway reflux in children; 15 s/frame, 1 hour

Gastric emptying: Omelette 18-37 MBq; normal ≤90% (1 h), ≤60% (2 h), ≤10% (4 h); < 30% at 1 hour rapid; Grade 1-3: 11-20% / 21-35% / >35%

Meckel's: 200 MBq; ranitidine preferred; NO thyroid blockade with perchlorate; sensitivity ~85% in children, ~60% in adults

GIBS: 550-1110 MBq; high success with transfusion ≥500 mL/24 hours; not performed for chronic occult bleeding

HIDA: Mebrofenin most common; 111-185 MBq; GBEF >40% normal (EANM); obesity/diabetes/CCB/OCP give falsely low GBEF; SOD criteria

Colonic transit: In-111 DTPA; ~70% excreted at 48 hours is normal

HMPAO → trapping by glutathione, 30 min stable (without stabiliser), shows luxury perfusion

ECD → trapping by esterases, 6 hours stable, may not show luxury perfusion

Both cross the BBB → assessment of parenchymal perfusion

"Freezes" the perfusion at the moment of injection → snapshot property

Crossed cerebellar diaschisis: reduced perfusion/metabolism in the cerebellar hemisphere contralateral to a supratentorial infarct/tumour (cerebellum normal on CT/MR)

Acetazolamide (1 g IV) reserve test: an area with exhausted reserve falls relative to baseline; contraindications are sulphonamide allergy and stroke within the last 3 days

Most intense uptake: Cerebral cortex, basal ganglia, thalamus

Sedative → may be given after injection (should not be given before)

Blood glucose should be <150-200 mg/dL (high blood glucose reduces brain FDG uptake)

Alzheimer: Bilateral temporoparietal + posterior cingulate/precuneus (earliest) → motor, visual cortex and basal ganglia spared

FTD: Frontal + anterior temporal → frontal dominant

DLB: Temporoparietal + occipital → occipital involvement distinguishes it from Alzheimer

Vascular: Multiple, asymmetric, scattered

CBD: Asymmetric frontoparietal

PSP: Frontal + mesencephalon

3 FDA-approved agents: Florbetapir (Amyvid), Florbetaben (Neuraceq), Flutemetamol (Vizamyl)

Positive: Grey-white matter contrast lost → widespread cortical uptake

Negative: Grey-white matter contrast preserved → strong negative predictive value

Positive amyloid PET ≠ definite Alzheimer (asymptomatic positivity in 10-30% of the elderly)

Appropriate use: Unexplained cognitive impairment, atypical presentation, early-onset dementia

Flortaucipir (Tauvid, 2020) and florquinitau (Tauklarify, 2026) → FDA-approved tau PET agents

Tau burden is directly proportional to cognitive decline (unlike amyloid)

Reflects Braak staging in vivo

Off-target: Choroid plexus (most common), basal ganglia, MAO-B

I-123 Ioflupane → binds DAT → integrity of presynaptic dopaminergic neurons

Normal: Bilateral symmetric comma/crescent shape (caudate + putamen)

Early Parkinson disease: Putamen ↓, caudate preserved → "dot" shape

Abnormal: Parkinson disease, DLB, MSA, PSP, CBD

Normal: Essential tremor, drug-induced parkinsonism, psychogenic, Alzheimer

Bupropion → stopped 8 days before (phentermine ~14 days)

Levodopa, dopamine agonists, SSRIs → need not be stopped

Dopa-responsive dystonia (Segawa) → DaTscan normal (distinguishes it from early-onset PD)

Interictal SPECT: Hypoperfusion → sensitivity 40-50% (low)

Ictal SPECT: Hyperperfusion → sensitivity 90-95% → injection within the first 20-30 s is critical

SISCOM: Ictal − interictal SPECT → MRI co-registration → best localisation

Interictal FDG PET: Hypometabolism → sensitivity 80-90% (in TLE)

Ictal FDG PET: Practically not feasible

Tuberous sclerosis: tubers are hypometabolic on FDG; the epileptogenic tuber shows increased uptake on C-11 AMT PET

Preferred: Tc-99m HMPAO (or ECD) → crosses the BBB → parenchymal perfusion

Findings: Empty skull + hot nose

Tc-99m DTPA/pertechnetate → flow only → posterior fossa inadequate

Unlike EEG, perfusion scintigraphy is not affected by barbiturates/sedatives or hypothermia

Intrathecal In-111 DTPA → preferred (long T½ → imaging at 24-48-72 hours)

Normal: 2-4 hours basal cisterns → 12-24 hours convexities → no ventricular uptake

NPH: Early ventricular reflux + ventricular persistence + convexity block → benefits from a shunt

CSF leak: Pledget/plasma ratio >1.5 → positive

VP shunt patency: Tc-99m DTPA injected into the shunt reservoir → arrival in the peritoneal cavity is assessed

Perfusion SPECT: HMPAO/ECD 740 MBq; ECD 30-60 min, HMPAO 30-90 min after; phenytoin → cerebellar, benzodiazepines → frontal hypoperfusion

FDG brain: 150-250 MBq; MSA-P → putamen-thalamus ↓, MSA-C → cerebellum ↓, PSP → frontal + midbrain ↓, CBD → asymmetry

Amyloid PET: Florbetapir 370, flutemetamol 185, florbetaben 300 MBq; sensitivity ~94%, specificity ~97%; breastfeeding 12 hours

Tau PET: 1st generation flortaucipir (off-target); 2nd generation MK-6240, PI-2620; rarely appropriate in CU individuals

DaTscan: 150-250 MBq; perchlorate 200 mg; breastfeeding 4 days; distinguishes ET, cannot distinguish PD/MSA/PSP; binding declines with age

FDOPA: Carbidopa increases uptake ~2-fold; antiparkinsonian drugs stopped ≥12 hours

Cisternography: In-111 DTPA 20 MBq; reaches the convexity at ~24 hours; persistent ventricular reflux in NPH

FDG-avid lymphomas: HL, DLBCL, Burkitt, MCL, FL, peripheral T-cell → PET/CT standard

FDG-non-avid lymphomas: SLL/CLL, marginal zone (MALT), Waldenström → CT-based assessment

PET/CT in HL → has replaced bone marrow biopsy

In NHL (especially low grade) bone marrow biopsy may still be needed

PET/CT changes the stage in 10-30% (usually upstaging)

Splenic involvement (Lugano): diffuse uptake more intense than the liver, focal lesion or splenomegaly (>13 cm)

Rising SUV in follicular lymphoma → suspected transformation → biopsy

Reference structures: Mediastinal blood pool and liver

Score 1: No uptake

Score 2: ≤ Mediastinum

Score 3: > Mediastinum, ≤ Liver

Score 4: > Liver (moderately)

Score 5: >> Liver and/or new lesion

Interim PET: 1-3 negative, 4-5 positive

End-of-treatment PET (Lugano): 1-3 negative (CMR), 4-5 positive

Modification of Ann Arbor → PET at the centre

Bulky "X" modifier removed → mass size reported in cm

CMR: Deauville 1, 2 or 3 + no new lesions

In FDG-non-avid lymphoma → CT-based response assessment

Interim PET: decision on treatment de-escalation/escalation in HL

End-of-treatment PET: ≥3 weeks after chemotherapy (preferably 6-8 weeks), 8-12 weeks after RT

PET positivity before autologous stem cell transplantation → post-transplant relapse/poor prognosis

Thymic hyperplasia (thymic rebound) → young patients, triangular, symmetric

Inflammation/granulation tissue

Infection

Sarcoid-like granulomatous reaction

Brown fat

High blood glucose → competitive inhibition

Small residual disease (5-7 mm)

Low-grade lymphoma

Early imaging after treatment

RCM: Cr-51 labelled red cells → binds to red cell haemoglobin

Plasma volume: I-125 labelled albumin (RISA)

Cr-51 elution: 1% per day → source of error in long studies

RCM increased → absolute erythrocytosis (PV, secondary)

RCM normal + Hct raised → relative erythrocytosis (Gaisböck syndrome)

Normal RCM: Men 25-35 mL/kg, women 20-30 mL/kg

Cr-51 labelled red cells → serial blood samples

Spleen/liver ratio >2:1 → splenic sequestration → splenectomy beneficial

Spleen/liver ratio <2:1 → hepatic/diffuse → no benefit expected from splenectomy

Heat-damaged Tc-99m red cells → spleen-specific

Heating: 49-50°C, 20 minutes (optimal)

>50°C → excessive damage → the liver also clears them

Indication: Accessory spleen, functional asplenia, ectopic splenic tissue

Tc-99m sulphur colloid → not spleen-specific (liver 85% dominant)

Anti-CD20 + Y-90 (pure beta emitter, T½ 64 hours)

No gamma emission → cannot be imaged

Rituximab given beforehand → clears normal B cells → increases delivery to the tumour

Dose: Plt ≥150K → 0.4 mCi/kg; Plt 100-149K → 0.3 mCi/kg; Plt <100K → contraindicated

Dose-limiting toxicity: Thrombocytopenia

Nadir: 7-9 weeks; recovery: ~12 weeks

Long-term risk: MDS/AML (2-5%)

HAMA (murine antibody): rapid blood clearance in subsequent antibody studies, false elevation in immunometric assays

I-131 Tositumomab (Bexxar) → withdrawn from the market in 2014

Tc-99m sulphur colloid → RES uptake → liver dominant (85%)

In-111 chloride → transferrin receptor → erythroid precursors → bone marrow-specific

Peripheral expansion → chronic anaemia, myeloproliferative disorder

Focal defect → metastasis, AVN, lymphoma infiltration

Extramedullary haematopoiesis → liver, spleen, paravertebral

FDG PET after G-CSF → diffuse bone marrow uptake → false positive → wait 2-4 weeks

Stage I: Single lymph node region (or single extranodal – IE)

Stage II: ≥2 regions on the same side of the diaphragm (or localised extranodal + adjacent LN – IIE)

Stage III: Both sides of the diaphragm (or above the diaphragm + spleen)

Stage IV: Disseminated extranodal organ involvement (bone marrow, liver parenchyma, lung)

A/B: B symptoms (fever >38°C, night sweats, >10% weight loss/6 months)

Body fluid volumes: Cr-51 red cells 0.5-1 MBq + I-125 HSA 0.1-0.2 MBq; outside ±25% of the theoretical value is abnormal; body/venous Hct 0.93

Platelet survival: In-111 oxinate; normal 8-10 days; splenic sequestration → splenectomy response ~80%

Heat-damaged red cells: 49.5°C, 20 min; 74-185 MBq; SPECT/CT + iterative reconstruction; not used to diagnose haemolysis

Zevalin: Rituximab on days 1 and 8, 11-14 MBq/kg (max ~1200 MBq); nadir 7-9 weeks (FDA and EANM); EU authorisation expired in 2024

FDG → entry into the cell via GLUT-1 → phosphorylation by hexokinase → cannot be dephosphorylated by glucose-6-phosphatase → metabolic trapping

F-18 half-life: 110 minutes, cyclotron production, positron emission, 511 keV annihilation photons

In obese patients SUVbw is artificially high → use SUVlbm (SUL)

Physiological uptake: brain (most intense), myocardium (variable), urinary tract (excretion), tonsils, GI tract

Brown fat: symmetric cervical-supraclavicular uptake → prevented with a warm environment + beta-blocker

Myocardial suppression: prolonged fasting (≥12-18 hours) + high-fat diet + heparin → cardiac sarcoidosis/endocarditis protocol

SPN: >8-10 mm nodule → PET indicated; SUVmax >2.5 suspicious for malignancy

Colorectal: strongest indication is detection of recurrence; mucinous type → false negative

Thyroid: high Tg + negative RAI → FDG PET/CT (flip-flop phenomenon → poor prognosis)

Testis: PET is useful for a residual mass >3 cm in seminoma; not reliable in non-seminoma (mature teratoma)

Prostate: low FDG sensitivity → PSMA PET/CT preferred

HCC: well-differentiated → takes up choline (not FDG); poorly differentiated → takes up FDG

Head and neck CUP: PET/CT can detect the primary focus in 25-30%

PET after RT: no earlier than 3 months (to let inflammation subside)

Incidental focal thyroid FDG uptake → malignancy risk ~30-35% → US ± FNAB; diffuse bilateral uptake → usually thyroiditis/Graves

Incidental focal colonic FDG uptake → colonoscopy (adenoma/carcinoma); diffuse/segmental → physiological, colitis or metformin

Negative PET/CT ~12 weeks after head and neck CRT → planned neck dissection can be avoided (PET-NECK)

Metabolic flare on days 7-10 after tamoxifen in ER+ breast cancer → not progression, a predictor of hormone response

Pilocytic astrocytoma (WHO grade 1) takes up FDG intensely → should not be mistaken for a high-grade tumour

RECIST 1.1: anatomical (CT), PR ≥30% decrease, PD ≥20% increase + 5 mm

PERCIST 1.0: metabolic (PET), PR/PD: ≥30% and ≥0.8 SUL unit change in SULpeak, parameter SULpeak

RECIST/PERCIST are not used in lymphoma → Lugano/Deauville is used

Most common: infection/inflammation (increased glycolysis in activated macrophages)

Talc pleurodesis → takes up FDG for years

G-CSF → diffuse bone marrow/splenic uptake → wait 2-4 weeks

Rebound thymic hyperplasia (young patients after chemotherapy)

Mnemonic BMLP-CHR: Bronchioloalveolar, Mucinous, Lobular breast, Prostate, Carcinoid, HCC (well diff.), Renal

Most common patient factor: hyperglycaemia

Technical: small lesion (<8 mm) → partial volume effect

Ga-68 PSMA → Lu-177 PSMA (prostate cancer)

Ga-68 DOTATATE → Lu-177 DOTATATE (NET)

I-123/I-131 MIBG → I-131 MIBG therapy (phaeochromocytoma, neuroblastoma)

FAPI: very low background, targets tumour stroma (CAF), not yet FDA approved

FES: oestrogen receptor, ER status in metastatic breast cancer (FDA approved 2020)

C-11 Methionine / F-18 FET: brain tumours → low background in the brain (unlike FDG)

F-18 Fluciclovine: prostate recurrence; use declining with PSMA

F-18 NaF: bone metastases, sensitivity superior to Tc-99m MDP

SUVmax: most widely used in clinical practice; simple but noise-sensitive

SULpeak: preferred in PERCIST

Patient factor that most affects SUV: blood glucose

Standardisation is critical for follow-up PETs: same scanner, same reconstruction, same uptake time

Patient preparation: ≥4-6 hours fasting, blood glucose <150-200 mg/dL, 60 min uptake time, warm/quiet environment

Greatest contribution of PET: atelectasis-tumour differentiation + detection of metabolically active lymph nodes

GTV definition methods: fixed SUV threshold, percentage threshold (40-50%), gradient-based, adaptive threshold → no consensus yet

4D-PET: respiratory gating → reduces motion artefact, useful for lesions at the lung bases and in the upper abdomen

FDG: glucose <11 mmol/L; wait ≥10 days after CT, >2 weeks after G-CSF, 2-3 months after RT, ≥6 weeks after surgery

PSMA: Ga-68 100-200 MBq; ganglia and benign bone lesions are false positives; PSMA-1007 hepatobiliary excretion

Fluciclovine: 370 MBq, imaging after 3-5 min; lytic > sclerotic uptake

FES: SUVmax <1.5 → no response to hormone therapy expected; fulvestrant is stopped ~28 weeks beforehand

Brain tumour: amino acid PET (FET/FDOPA/MET) superior to FDG; dynamic FET early peak → high grade

PentixaFor (CXCR4): myeloma, MCL, MZL; APA detection in primary aldosteronism

SLN = the first lymph node reached by lymphatic drainage from the primary tumour

SLN negative → distal nodes 95-98% negative → unnecessary radical dissection is avoided

Popularised the concept: Donald Morton (melanoma), Armando Giuliano (breast)

Small particle → fast transport + low retention

Large particle → slow transport + high retention

Tc-99m Tilmanocept (Lymphoseek): specific binding to the mannose receptor (CD206) → receptor-based (not passive filtration) → fast transport + high retention → FDA approved (2013)

USA: Tc-99m sulphur colloid (filtered); Europe: Tc-99m nanocolloid

Tc-99m HSA is not a colloid → shows lymphatic channels, not retained in the SLN

Breast: peritumoral, subareolar (all quadrants drain to the subareolar plexus), intradermal

Intratumoral injection is not recommended → may be trapped within the tumour

Melanoma: intradermal, at 2-4 points around the lesion/scar

Isosulfan blue: anaphylaxis 1-2%

Pulse oximetry artefact → SpO2 artificially low (not true hypoxia)

Methylene blue + SSRI → serotonin syndrome (MAOI effect)

Change in urine colour (transient, blue-green)

ACOSOG Z0011: early breast Ca, cN0, 1-2 positive SLNs → ALND not needed (when breast-conserving surgery + RT is planned)

MSLT-II: SLN-positive melanoma → CLND vs observation → no difference in survival → US surveillance sufficient instead of CLND

Breslow thickness ≥0.8 mm (or <0.8 mm + adverse prognostic factors)

SLN status → strongest prognostic factor

Lymphoscintigraphy is critical in truncal melanoma → drainage pattern unpredictable (30-40% unexpected drainage)

SPECT/CT very useful in head and neck melanoma (complex anatomy)

SLN positivity rises with Breslow: <1 mm ~5%, 1-4 mm ~15-25%, >4 mm ~30-40%

An interval (in-transit) node (e.g. popliteal, epitrochlear) is also accepted as an SLN and removed

10% rule (SLN): ≥10% of the highest ex vivo count → accepted as SLN

20% rule (parathyroid): ex vivo count more than ≥20% of background → parathyroid tissue

Do not confuse these two rules!

For SLNs close to the injection site → injection-site activity masks the SLN

Most common: in breast cancer when the tumour is close to the axilla

Solution: SPECT/CT, lead shield, delayed imaging, probe approach from a different angle

Most specific finding: dermal backflow

Liver uptake = normal lymphatic function (lymph → venous system → hepatic RES)

Absence of liver uptake = severe lymphatic insufficiency

Primary lymphoedema: aplasia (no channels), hypoplasia (few/thin channels), hyperplasia (dilated/tortuous – rare)

Most common cause of secondary lymphoedema: surgery + RT; most common worldwide: filariasis

ROLL: localisation of a non-palpable breast lesion (intratumoral Tc-99m + gamma probe)

SNOLL: ROLL + SLN biopsy in a single session

RSL: localisation with an I-125 seed (low energy 27-35 keV, half-life 59.4 days)

Radioguided parathyroidectomy: Tc-99m MIBI + gamma probe → minimally invasive surgery

NaI(Tl): high sensitivity, widespread, affected by moisture

CsI(Tl): compact, robust

CZT: excellent energy resolution, works at room temperature, compact, expensive

Scintillation probes superior at high energy (I-131, 511 keV); semiconductor probes compact, better energy resolution

Vulvar cancer: early stage, bilateral inguinofemoral SLN

Cervical cancer: early stage, cervical injection

Merkel cell carcinoma: aggressive; SLN recommended for staging

Endometrial cancer: cervical injection with ICG, fluorescence in robotic surgery

Oral cavity SCC: early stage, being investigated as an alternative to elective neck dissection

Colloid sizes: nanocolloid 5-80 nm, rhenium sulphide 50-200 nm, tilmanocept ~7 nm (CD206)

Strongest SLN criterion is the lymphatic channel; the hottest node is not always the SLN; SPECT/CT mandatory in OSCC

In pregnancy a one-day protocol with 10-15 MBq; ~1.2 µSv/MBq for small colloids

Semi-quantitative lymphoscintigraphy: 37-50 MBq, 15 min treadmill; normal inguinal uptake >14% (Co-57) / >9% (BMI)

EANM Dosage Card or North American Consensus Guidelines → standard references

3 kg → multiplier 1 (baseline activity), 68 kg → multiplier 14 (adult dose)

Do not go below the minimum dose → inadequate image → repeat study → more radiation

Giving the adult dose directly is never acceptable

Webster and Clark rules are historical and not recommended in current practice

DMSA: most sensitive method for acute pyelonephritis (90-95%), imaging after 2-4 hours

Acute pyelonephritis → swelling; renal scar → volume loss, contour retraction → follow-up DMSA after 6 months to differentiate

MAG3: preferred for paediatric diuretic renography → tubular secretion → good images even at low GFR

DTPA is inadequate in neonates (low GFR)

Diuretic renography T½: <10 min normal, 10-20 min indeterminate, >20 min obstruction

Bladder catheter → prevents the back-pressure effect (pseudo-obstruction)

In neonates wait 4-6 weeks (renal maturation)

Initial assessment → VCUG (anatomical detail, grading, urethral assessment)

Follow-up → DRC (50-100 times lower radiation dose)

Indirect cystography → no catheter needed, in toilet-trained children

Drugs that reduce MIBG uptake: tricyclic antidepressants, cocaine, amphetamine (uptake-1 inhibition); reserpine (inhibition of vesicular storage); labetalol (uptake-1 inhibition); phenylephrine, pseudoephedrine (competitive inhibition)

The most common extracranial solid tumour of childhood

Neural crest origin, most often the adrenal medulla

Diagnostic MIBG → I-123 preferred (low energy, SPECT possible, low dose)

90-95% of neuroblastomas are MIBG-positive

MIBG-negative → FDG PET/CT or F-18 DOPA PET

Thyroid blockade is mandatory (KI or Lugol, start 24 hours before)

Stage 4S (MS): <12 months (<18 months in INRGSS), localised + limited metastases → spontaneous regression may occur

Curie score: 9 skeletal segments + soft tissue → each 0-3 → max. 30 → response monitoring → ≤2 good prognosis

MYCN amplification → poor prognosis

Growth plates → bilateral symmetric intense uptake = normal

Asymmetry → pathology (infection, trauma, tumour)

Child abuse (NAI): skeletal survey (radiography) primary + bone scintigraphy complementary

Disadvantage of bone scintigraphy: low sensitivity for skull fracture and classic metaphyseal lesion (CML)

Legg-Calvé-Perthes: early stage → cold lesion in the femoral head (avascular phase)

Neonatal osteomyelitis: may be a photopenic (cold) lesion → beware false negative!

Ewing sarcoma → diaphysis, osteosarcoma → metaphysis

Toddler's fracture (1-3 years): radiography often negative; on bone scintigraphy faint diffuse or oblique linear uptake along the tibia

Langerhans cell histiocytosis: lesions may be normal/cold on bone scintigraphy → radiographic skeletal survey is the mainstay; FDG PET/CT more sensitive

Perthes prognosis (Conway): early activity in the lateral column is good; neovascularisation from the base of the femoral head indicates poor prognosis

Tamponade in hip effusion (septic arthritis/transient synovitis) → reduced uptake in the femoral head in all phases → urgent decompression

Ewing sarcoma: FDG PET/CT more sensitive than bone scintigraphy for bone/bone marrow metastases

Meckel scintigraphy: Tc-99m pertechnetate → uptake in ectopic gastric mucosa

GER scintigraphy: lung activity on delayed images → pulmonary aspiration (most important finding)

Image Gently (2008) → campaign to reduce radiation dose in paediatric imaging

Go With the Guidelines → Image Gently + SNMMI nuclear medicine campaign

Increased risk in children: high cell division rate + long life expectancy + small body size

Feed-and-sleep technique → alternative to sedation in infants <1 year

Breastfeeding interruption: Tc-99m → most ≤4 hours (pertechnetate/MAA 12 h), I-123 NaI → 3-4 days, I-131 → stop completely

EANM dosage card: paediatric dose = baseline activity × multiplier; 3 kg → 1, 30 kg → 6.86, ≥68 kg → 14

Paediatric minimum activities: pertechnetate (thyroid) 10, MAG3 15, DMSA 18.5, DTPA/HIDA/Meckel/RBC 20, FDG 26, I-123 MIBG 37, bone 40, brain perfusion 100 MBq

I-123 MIBG thyroid blockade 2-3 days; diagnostic I-131 MIBG 5-10 days

Uptake mechanism: multiple → transferrin, lactoferrin, siderophores (bacteria-specific), leucocyte uptake

Half-life: 78.3 hours, gamma energies: 93, 185, 300, 394 keV

Imaging: 48-72 hours after injection, medium-energy collimator

Normal biodistribution: liver > spleen > bone marrow + kidney (early) + bowel (late)

Sarcoidosis patterns: Panda (parotid + lacrimal) + Lambda (bilateral hilar + right paratracheal) → together highly specific

Today replaced by FDG PET/CT for many indications

In-111 oxine: NO kidney/bladder uptake, NO bowel uptake (up to 24 hours) → preferred for abdominal infection

Tc-99m HMPAO: kidney/bladder uptake PRESENT, bowel uptake PRESENT → better image quality, same-day result

Dual isotope (In-111 leucocytes + Tc-99m sulphur colloid): discordant = infection, concordant = bone marrow

Unreliable in spinal osteomyelitis → false negative → FDG PET/CT is preferred

Virgin bone: three-phase bone scintigraphy (first step) → if positive, labelled leucocytes

Complicated (prosthesis, fracture, Charcot): labelled leucocytes + bone marrow (dual isotope) → gold standard

Spinal: FDG PET/CT is preferred (labelled leucocytes unreliable)

Diabetic foot: dual isotope → over 90% accuracy → best for Charcot vs osteomyelitis

Strongest indication: FUO (50-70% diagnostic contribution)

Negative FDG PET/CT → high negative predictive value

Most important limitation: cannot distinguish infection from malignancy

In spinal osteomyelitis: sensitivity 96%, specificity 91%

FDG PET/CT → added to the Duke criteria as a major criterion (2015 ESC)

Myocardial suppression: ≥12-18 hours fasting + low-carbohydrate/high-fat diet + IV heparin

Limited role in native valves (physiological myocardial uptake)

Added value: whole-body scanning for septic emboli

FDG PET/CT → most valuable method (sensitivity 93-100%)

Focal uptake + perigraft gas → highly specific for infection

Diffuse mild uptake may be normal in the first 4-8 weeks postoperatively

Most specific pattern: perfusion defect + focal FDG uptake (mismatch)

Burned-out: perfusion defect + NO FDG uptake → scar

Myocardial suppression: same as the endocarditis protocol

Focal-on-diffuse uptake → may be active sarcoidosis BUT may be confused with inadequate suppression

FDG PET/CT → detects vascular inflammation early (prestenotic phase)

Grading: comparison with the liver → Grade 3 (vascular > liver) = active vasculitis

Vasculitis: diffuse smooth linear uptake; atherosclerosis: focal irregular uptake

Takayasu: young woman <40 years; giant cell arteritis: >50 years, temporal + large vessels

Ga-67: critical organ colon; marked bilateral renal uptake after 24 hours is pathological → acute interstitial nephritis (not expected in ATN)

With In-111-WBC the critical organ (highest dose) is the spleen

Normal chest radiograph + diffuse bilateral lung Ga-67 uptake → PCP; Kaposi sarcoma Ga-67-negative/Tl-201-positive

In IBD early imaging with Tc-99m HMPAO-WBC (30 min–2-3 hours) is essential → after that physiological bowel activity misleads

In acute osteomyelitis bone scintigraphy becomes positive at 24-72 hours; radiography at ~10-14 days

WBC: Tc-99m-WBC 185-370 MBq, In-111-WBC 10-18 MBq; positivity = uptake increasing over time; In-111-WBC preferred in the abdomen

Anti-granulocyte MoAb: besilesomab (NCA-95, HAMA → single administration), sulesomab (NCA-90, Fab', no HAMA)

Infection FDG: 175-350 MBq; SUV not validated; steroids deferred; no recommendation to stop antibiotics

Radiopharmaceutical: Tc-99m pertechnetate/DTPA → drop into the lower conjunctival sac

Non-invasive, physiological assessment (contrast dacryocystography is invasive and anatomical)

Normal drainage: lacrimal sac (2-5 min) → nasolacrimal duct (5-10 min) → nasal cavity (10-15 min) → nasopharynx (15-20 min)

Superior to contrast methods for detecting functional epiphora

Complete obstruction: accumulation proximal to the obstruction, no passage distally

Tc-99m pertechnetate IV → NIS-mediated uptake

Acid stimulation (20 min) → normal: rapid washout

Sjögren: reduced uptake + delayed/absent washout (Grade 1-4)

Sialolithiasis: normal/increased uptake + NO washout (duct blocked, gland intact)

Warthin tumour: TAKES UP pertechnetate ("hot" nodule) → oncocytic cells, rich in mitochondria

Pleomorphic adenoma: does NOT take up pertechnetate ("cold" nodule)

Sialadenitis after I-131: reduced uptake + reduced washout (dose-dependent)

Intraperitoneal injection of Tc-99m MAA

Shunt patent → MAA passes into the venous system → lung uptake

Shunt occluded → activity remains in the peritoneal cavity → NO lung uptake

If Tc-99m sulphur colloid is used → liver/spleen uptake with a patent shunt

Tc-99m pertechnetate IV → angiographic phase + static phase

Acute torsion (<6 hours): reduced flow + COLD area

Late torsion (>24 hours): central COLD + peripheral HALO (ring of increased activity) → testis cannot be salvaged

Epididymitis/orchitis: increased flow + HOT area → the exact opposite of torsion

The bell clapper anomaly predisposes to torsion and is often bilateral

The halo pattern is not specific to late torsion: also seen in abscess, haematoma and necrotic tumour

Torsion of the appendix testis: scintigraphy normal or focally increased ('hot dot'); false-negative torsion: spontaneous/intermittent detorsion

Today largely replaced by colour Doppler US

Oral Co-57/Co-58 labelled vitamin B12 → 24-hour urinary excretion measured

Phase 1 low + Phase 2 normal (corrected by adding IF) → pernicious anaemia

Phase 1 and Phase 2 low (adding IF does not correct) → ileal disease (Crohn, resection)

Not used today → Co-57/Co-58 production stopped → serological tests (anti-IF Ab, methylmalonic acid) are used

Cr-51 → red cell mass measurement + red cell survival

Normal red cell lifespan: 120 days (Cr-51 T½ = 25-35 days)

Polycythaemia vera vs relative polycythaemia: Cr-51 red cell mass → increased in PV, normal in relative polycythaemia

Spleen/liver ratio >2:1 → splenic sequestration → splenectomy beneficial

I-125 albumin → plasma volume measurement

In-111 oxine → platelet survival (normal: 8-10 days)

Tc-99m DTPA → percutaneous injection into the shunt reservoir (Ommaya/Rickham)

Patent shunt: activity progresses along the shunt line to the peritoneal cavity

Occluded shunt: activity does not progress → the level of occlusion is determined

Localised focal collection at the distal tip (no free spread in the peritoneum) → CSF pseudocyst/loculation

Cimetidine (H2 blocker): inhibits pertechnetate secretion → retention in the gland increases → target/background ratio increases (started 48 hours before the study)

Pentagastrin: increases pertechnetate uptake by gastric mucosal cells

Glucagon: reduces bowel motility → reduces artefact

Oral Tc-99m sulphur colloid (before going to bed at night) → morning lung imaging

Activity in the lungs → evidence of aspiration

Especially in paediatric patients (recurrent pneumonia, chronic cough)

Dacryoscintigraphy → physiological (scintigraphy) vs anatomical (contrast) assessment

Salivagraphy → Sjögren vs sialolithiasis (reduced vs normal/increased uptake)

Warthin tumour (and oncocytoma) → salivary gland tumours that take up pertechnetate

LeVeen shunt → MAA IP → lung uptake if patent

Testicular scintigraphy → torsion COLD, epididymitis HOT

Schilling test → historical, not used today

Salivary gland scintigraphy: 37 MBq; parenchyma vs outflow; breastfeeding 12 hours

Shunt scintigraphy: subcutaneous injection mimics distal occlusion → vertex view

Fixed dose in Graves: 10-15 mCi, in TMNG: 15-30 mCi

Calculated dose formula: 3 parameters → target dose (µCi/g), gland weight (g), 24-hour RAIU (%)

Antithyroid drugs: methimazole stopped 2-5 days before, PTU 2-8 weeks before with fixed activity ( 4-7 days with the dosimetric approach) (radioprotective effect)

Graves ophthalmopathy: mild active → I-131 can be given with steroid prophylaxis; moderate-severe active → avoid I-131

Most important risk factor (worsening ophthalmopathy): smoking

Most common outcome: hypothyroidism (50-80%)

In toxic adenoma the surrounding tissue is spared → suppressed tissue does not take up iodine

RAI in paediatric Graves: avoided under age 5; acceptable at age 5-10 if activity is <10 mCi (ATA 2016)

TSH stimulation: THW → TSH >30 mIU/L or rhTSH (Thyrogen) 0.9 mg IM × 2 days

Stunning effect: diagnostic I-131 (>3 mCi) → reduces NIS expression → use I-123 or low-dose I-131 (≤3 mCi)

Low-risk ablation: 30 mCi, high risk: 100-200 mCi

Post-therapy WBS: 5-7 days after treatment → more sensitive than the diagnostic scan

Most common side effect: sialadenitis; most serious late complication: secondary malignancy (AML) → cumulative >600 mCi

Flip-flop phenomenon: I-131 uptake ↓, FDG uptake ↑ → dedifferentiation

TENIS syndrome: high Tg + negative I-131 scan → FDG PET/CT indicated

RAI-refractory: tyrosine kinase inhibitors (lenvatinib, sorafenib)

ATA 2015 excellent response: suppressed Tg <0.2 or stimulated Tg <1 ng/mL + imaging negative

Age threshold 55 in AJCC 8 DTC staging: under 55 only stage I (M0) or II (M1)

Thyroid blockade mandatory (SSKI/potassium iodide)

Drugs that reduce MIBG uptake: tricyclic antidepressants, labetalol, reserpine, sympathomimetics

Most important dose-limiting toxicity: bone marrow suppression

NETTER-1: advanced midgut NET → marked superiority in PFS

Protocol: 7.4 GBq × 4 cycles, 8 weeks apart

Renal protection: lysine + arginine amino acid infusion → reduces reabsorption by 40-50%

Patient selection: Ga-68 DOTATATE PET/CT positive, well-differentiated (Grade 1-2)

Renal dose limit: cumulative ≤23 Gy

VISION: OS advantage of 4 months in mCRPC (15.3 vs 11.3 months, HR 0.62)

PSMAfore: rPFS 12.0 vs 5.6 months in taxane-naive mCRPC

Protocol: 7.4 GBq × 6 cycles, 6 weeks apart

Patient selection: PSMA PET/CT positive → PSMA-negative lesion = poor prognosis

Most common side effects: fatigue, xerostomia, nausea; most common serious (Grade ≥3) toxicity: bone marrow suppression

ALSYMPCA: OS advantage of 3.6 months in mCRPC with bone metastases (14.9 vs 11.3 months)

Alpha emitter → range 100 µm → acts only at the bone surface

Protocol: 55 kBq/kg × 6 cycles, 4 weeks apart

Contraindications: visceral metastases, combination with abiraterone (ERA-223 → fracture risk)

Response marker: decline in ALP

Tc-99m MAA shunt study mandatory → hepatopulmonary shunt >20% → contraindicated

Shunt <10% → full dose; 10-15% → reduce by 20%; 15-20% → reduce by 40%

Glass microspheres: high specific activity (2500 Bq), few microspheres, little embolisation

Resin microspheres: low specific activity (50 Bq), many microspheres, more embolisation

TACE contraindicated in portal vein thrombosis → Y-90 can be given (advantage)

Lung dose limit: ≤30 Gy per session, ≤50 Gy cumulative

Normal liver dose limit: healthy ≤70 Gy, cirrhotic ≤40 Gy

Sr-89: pure beta, T½ 50.5 days, Ca analogue, no imaging, response in 2-4 weeks

Sm-153: beta + gamma (103 keV), T½ 46.3 hours, phosphonate, imaging possible, response in 1 week

Myelosuppression more marked with Sr-89 (long T½)

Purely lytic lesions without uptake on bone scintigraphy (e.g. multiple myeloma) do not respond; shortest beta range in tissue is Sm-153 (~0.6 mm)

Anti-CD20 + Y-90 → B-cell NHL

Crossfire effect: beta range ~5 mm → also kills neighbouring cells

Dose: PLT ≥150K → 0.4 mCi/kg; PLT 100-149K → 0.3 mCi/kg; PLT <100K → contraindicated

Most important toxicity: delayed myelosuppression (nadir 7-9 weeks)

Large joint (knee): Y-90 (range 11 mm)

Medium joint (shoulder, hip): Re-186 (range 3.6 mm)

Small joint (finger): Er-169 (range 1 mm)

Immobilisation for 48-72 hours after injection → prevents extra-articular leakage

MIRD formula: D = Ã × S

I-131 bone marrow limit: ≤200 cGy (2 Gy)

I-131 lung retention: at 48 hours ≤80 mCi

NRC release: <7 mR/hour at 1 metre OR residual activity <33 mCi

Breastfeeding after I-131: must be stopped (permanently for that child)

Ra-223, Y-90, Lu-177: minimal external radiation risk → no special isolation needed

Benign thyroid: stop thiamazole 2-5 days and PTU 2-8 weeks before (4-7 days with the dosimetric approach); wait 6-8 weeks after iodinated contrast; adenoma 300-400 Gy, TMNG >150 Gy

Ra-223: for subsequent doses ANC ≥1.0 and PLT ≥50×10⁹/L; excretion mainly faecal

Sr-89: standard 150 MBq; GFR <30 mL/min → not given; calcium stopped 2 weeks before

Y-90 RE: tumour dose in HCC: glass ≥205 Gy, resin ≥120 Gy; Ho-166 scout ~250 MBq, tumour ≥60 Gy

Lu-177 PSMA: highest doses in lacrimal/salivary glands and kidney; Ac-225 PSMA: 100 kBq/kg, xerostomia

EANM optimisation levels: L1 (cohort) – L2 (patient-specific dosimetry) – L3 (absorbed-dose-based prescription)

First daily test: energy peak check (peaking) → if the photopeak is wrong, everything is affected

Daily uniformity: intrinsic = without collimator + point source (5 × FOV); extrinsic = with collimator + flood source

Uniformity formula: IU = (Max − Min) / (Max + Min) × 100%

Acceptable integral uniformity: ≤3-5% (intrinsic), ≤5% (extrinsic)

Minimum counts: 3-5 million (daily), >30-100 million (annual high-count)

Weekly: spatial resolution and linearity with a bar phantom

COR test: every 3-6 months, acceptable error ≤0.5 pixel

SPECT ring artefact → non-uniformity

SPECT doubling → COR error

NaI(Tl) energy resolution: 9-10% (at 140 keV)

A planar non-uniformity of ~1% can grow to ~20% in SPECT → correction map: ~30 million counts at 64×64, ~120 million at 128×128

Co-57 sheet source (versus a Tc-99m liquid phantom): no preparation, constant thickness, no bubble/poor-mixing artefacts, low staff dose

Multiple window spatial registration (MWSR): superimposition of window images for multi-peak nuclides such as Ga-67/In-111; blurring when faulty

Daily QC source: Ge-68 (T½ = 271 days, positron emitter)

PET spatial resolution: 4-6 mm (FWHM)

SUV accuracy: ±10% acceptable

NECR: Noise Equivalent Count Rate → determines the optimal activity range

Streak artefact on the sinogram → faulty detector block

Partial volume effect: becomes marked when lesion diameter is <2-3 × resolution

IEC body phantom: 6 spheres (10-37 mm) → contrast recovery assessment

Daily: constancy → Cs-137 → ±5%

Annual: accuracy → NIST-traceable → ±5%

Every 6 months or annually: linearity → decaying source → ±10%

At installation: geometry dependence

Accuracy, linearity and geometry tests are repeated after a major repair or relocation

Radionuclidic purity: gamma spectrometry → Mo-99 breakthrough: ≤0.15 µCi/mCi Tc-99m

Mo-99 test: lead container (6 mm Pb) → Tc-99m is absorbed, Mo-99 passes through

Radiochemical purity (RCP): TLC → ≥90% (most Tc-99m kits; FDG/Ga-68 ≥95%)

Free TcO₄⁻: ITLC-SG + acetone → TcO₄⁻ migrates to the front

Colloid (TcO₂): ITLC-SG + saline → TcO₂ remains at the origin

Uptake of free TcO₄⁻: thyroid, stomach, salivary glands

Uptake of TcO₂ (colloid): liver, spleen, bone marrow

Chemical purity: Al³⁺ ≤10 µg/mL (colorimetric test) → risk of flocculation in sulphur colloid

FDG: Kryptofix ≤50 µg/mL, RCP ≥95%, pH 4.5-8.5

MAA particle size: 10-90 µm, number: 200,000-700,000

Pulmonary HT / right-to-left shunt → number of MAA particles reduced (≤100,000)

ICRP 103 occupational dose: 20 mSv/year (5-year average), ≤50 mSv in a single year

NRC occupational dose: 50 mSv/year (5 rem/year) → different from ICRP!

Lens of the eye (ICRP 118): 20 mSv/year (previously 150 mSv/year → an important change)

Public dose limit: 1 mSv/year

Fetal dose in a pregnant worker: ICRP → ≤1 mSv; NRC → ≤5 mSv (0.5 rem)

Medical event: >20% deviation + organ dose >50 rem or effective dose >5 rem

NRC notification: 1 day by telephone + 15 days written report

ALARA: time, distance, shielding

Radiation area: at 30 cm >5 mrem/hour

High radiation area: at 30 cm >100 mrem/hour

Unrestricted area limit: 2 mrem/hour

DIS: 10 half-lives are allowed → activity falls to ~1/1000

Tc-99m DIS: ~60 hours; I-131 DIS: ~80 days; F-18 DIS: ~18 hours

After DIS: radioactive labels must be removed → disposed of as normal waste

Long-lived waste (T½ >120 days): DIS cannot be applied → licensed facility

Mixed waste: most difficult to dispose of → subject to both NRC and EPA regulations

Discharge to the sewer: ≤1 Ci in total per year

Transport labels: White-I (TI = 0, surface ≤0.5), Yellow-II (TI ≤1, surface ≤50), Yellow-III (TI ≤10, surface ≤200)

Wipe test limit: 200 dpm/100 cm²

Decontamination: no harsh scrubbing → skin integrity is broken → absorption increases.

Dose calibrator: action level 3%, tolerance limit 5%; linearity at intervals of ≥6 months; reference source T½ >5 years (Cs-137)

Mo-99 breakthrough: eluate purity test; first eluate, repeated after >14 days; European limit 0.1%

SPECT/CT alignment ≤5 mm; PET/CT alignment every 6 months; daily PET QC with a Ge-68 phantom or Lu-176 (LSO)

Probe: ~200 kBq Co-57 for daily constancy; EARL → quantitative harmonisation between centres

Theranostics: "See it → Treat it" → diagnosis + treatment directed at the same molecular target

Theranostic pair: same ligand + different radionuclides (diagnostic + therapeutic)

The most important theranostic pairs:

NETTER-1: Lu-177 DOTATATE → midgut NET → PFS prolonged

VISION: Lu-177 PSMA-617 → mCRPC → OS and rPFS prolonged

Patient selection is critical: target expression must be confirmed by imaging

NET – Krenning score ≥2 → suitable for PRRT

Prostate – PSMA PET positive + no discordant disease → suitable for PSMA therapy

Discordant disease: PSMA-negative / FDG-positive → poor prognosis, low response to PSMA therapy

Cumulative kidney dose limit: 23 Gy (PRRT)

Renal protection: amino acid infusion (lysine + arginine)

High LET (~80-100 keV/µm) → double-strand DNA breaks

Short range (50-80 µm) → minimal damage to surrounding tissue

OER ~1 → effective in hypoxic tumours too

Ac-225 PSMA: promising in mCRPC refractory to Lu-177

Ra-223: approved alpha therapy → osteoblastic bone metastases

Disadvantage: recoil effect of daughter radionuclides → detachment from the target

Target: FAP (Fibroblast Activation Protein) → cancer-associated fibroblasts

Most important advantage: low physiological background (brain, liver)

Superior to FDG: peritoneal carcinomatosis, brain tumours, HCC, gastric/colorectal cancer

No patient preparation required (no fasting or blood glucose control)

Not tumour-specific → also taken up in wound healing, fibrosis and inflammation

Therapeutic potential: Lu-177 FAPI, Ac-225 FAPI → at the research stage

Problem: short tumour retention → limited therapeutic efficacy

F-18 PSMA-1007: alternative to Ga-68 PSMA → longer T½, central distribution → disadvantage: bone false positives

Zr-89: T½ = 78.4 hours → immuno-PET → suited to antibody pharmacokinetics

Cu-64: T½ = 12.7 hours → both β⁺ and β⁻ → theranostics in a single radionuclide

Ga-68 Pentixafor: CXCR4-targeted → haematological malignancies

CNN: the most common deep learning architecture for image analysis

U-Net: medical image segmentation

Dose reduction: AI denoising of low-count images → 50-75% dose reduction

Radiomics: extracting quantitative features from images

1st order: histogram (mean, SD, skewness)

2nd order: texture analysis (GLCM, GLRLM)

Higher order: filter-based (wavelet, LoG)

Challenges: data quality, generalisability, explainability ("black box"), regulatory approval

uEXPLORER: axial FOV = 194 cm → the first total-body PET/CT

Biograph Vision Quadra: axial FOV = 106 cm

Conventional PET: axial FOV = 15-30 cm

Increase in sensitivity: ~40-fold (uEXPLORER)

Options for use: ultra-low dose OR ultra-fast OR ultra-high quality

Dynamic whole-body imaging: simultaneous kinetic analysis in all organs → dosimetry in a single session

SiPM: a semiconductor photon detector replacing the PMT

Timing resolution: ~200 ps (PMT: ~500 ps)

Energy resolution: ~9-11% (PMT: ~12-15%)

TOF formula: Δx = c × Δt / 2

CZT: direct-conversion detector (gamma → electrical, no intermediate step)

Energy resolution: ~5-6% (NaI(Tl): ~9-10%)

Cardiac CZT-SPECT: 5-8-fold increase in sensitivity → 2-5 min acquisition, 50% dose reduction

Crystal comparison: LYSO (most common in modern PET) > LSO > BGO (older) | NaI(Tl) → SPECT

Photon-counting CT: counts each photon individually → spectral information → material decomposition

Compton camera: collimator-free → potential for very high sensitivity → not yet in clinical use.

SSTR antagonists (JR11, LM3, LM4): less internalisation, higher contrast in the liver; haematotoxicity with JR11

GRPR: pan-tumour target (prostate, breast); highest physiological expression in the pancreas

Immuno-PET: checkpoint antibodies with Zr-89; F-18 AraG for T-cell activation; FAP-high CAF → immunosuppression

iNM: hybrid tracer ICG-Tc-99m-nanocolloid; SLN false negatives 1-14%

AI: radiomics has the advantage on small data; 'no free lunch' → several models; interpretability ≠ explainability

2×2 table: the basis of all calculations → TP, FP, FN, TN

Sensitivity = TP / (TP + FN) → catching disease → priority in screening tests

Specificity = TN / (TN + FP) → recognising the healthy → priority in confirmatory tests

PPV = TP / (TP + FP) → prevalence-dependent → prevalence ↑ → PPV ↑

NPV = TN / (TN + FN) → prevalence-dependent → prevalence ↑ → NPV ↓

Sensitivity and specificity are INDEPENDENT of prevalence (intrinsic properties of the test)

SnNOut: high Sensitivity + Negative result → rule disease out

SpPIn: high Specificity + Positive result → rule disease in

LR+ > 10: strong diagnostic evidence (rules disease in)

LR− < 0.1: strong diagnostic evidence (rules disease out)

LR is independent of prevalence → its advantage over PPV/NPV

Normal distribution: ±1 SD ~68%, ±1.96 SD 95%, ±3 SD ~99.7%; standard error of a proportion = √[p(1−p)/n]

Decision tree: square = decision node, circle = chance node, triangle = outcome; expected value = Σ probability × outcome

X axis: 1 − Specificity (FPR) | Y axis: Sensitivity (TPR)

AUC = 1.0: perfect | AUC = 0.5: chance level (diagonal) | AUC <0.5: worse than chance

Youden index: J = Sensitivity + Specificity − 1 → optimal threshold

DeLong test: statistical comparison of two AUCs

Strongest evidence: systematic review / meta-analysis > RCT > cohort > case-control > cross-sectional

RCT: can establish causality → randomisation balances confounders

Cohort: measures RR → unsuitable for rare diseases

Case-control: measures OR → most suitable for rare diseases → retrospective

Cross-sectional: measures prevalence → no temporal relationship can be established

Cumulative incidence (cohort) ≠ prevalence (cross-sectional, existing cases at a given time)

Phase 0 microdose (PK/biodistribution) → Phase I safety/dose → Phase II preliminary efficacy → Phase III comparative RCT → Phase IV post-marketing

ITT analysis: all randomised patients are analysed according to their initial groups

Meta-analysis: forest plot, I² (heterogeneity), funnel plot (publication bias)

I² > 75%: high heterogeneity

Type I error (α): saying there is a difference when there is none → false positive → usually 0.05

Type II error (β): saying there is no difference when there is one → false negative → usually 0.20

Power = 1 − β → usually ≥ 80% is targeted

Increases power: sample ↑, effect size ↑, α ↑, variance ↓

p value ≠ probability that H₀ is true (the most common misunderstanding!)

Statistical significance ≠ clinical significance → effect size and NNT should be assessed

NNT = 1/ARR → low NNT = effective treatment

Confidence level ↑ (95% → 99%) → interval widens; sample ↑ → interval narrows

Fisher's exact test: expected frequency < 5 → used instead of chi-square

Bonferroni correction: α / number of tests in multiple comparisons → very conservative

Formula: κ = (P₀ − Pₑ) / (1 − Pₑ)

κ = 1: perfect agreement | κ = 0: chance level | κ < 0: worse than chance

Landis & Koch: 0.41-0.60: moderate | 0.61-0.80: substantial | 0.81-1.00: almost perfect

Cohen's kappa: 2 observers, nominal data

Weighted kappa: ordinal data

Fleiss' kappa: >2 observers

ICC: agreement for continuous data

Bland-Altman: comparison of two measurement methods

Four basic principles (Beauchamp & Childress):

1. Autonomy → the patient's right to decide → informed consent 2. Beneficence → acting in the patient's interest 3. Non-maleficence → ALARA, justification 4. Justice → equal distribution of resources

The 3 ICRP principles: Justification + Optimisation (ALARA) + Dose limitation

ALARA → the reflection of non-maleficence in radiation protection

Nuremberg Code (1947): requirement for voluntary consent → after the Nazi experiments

Declaration of Helsinki (1964): ethics of research on human subjects → World Medical Association

Belmont Report (1979): respect for persons, beneficence, justice

5 elements: Disclosure, Understanding, Voluntariness, Decision-making capacity, Consent

Diagnostic nuclear medicine: verbal consent is usually sufficient

Therapeutic nuclear medicine (RAI, PRRT, PSMA): written consent is mandatory

Pregnancy: RAI therapy absolutely contraindicated → a pregnancy test before treatment is mandatory

Paediatric: Image Gently → dose reduction, EANM dosage card, strict justification

Breastfeeding: the interruption varies with the radiopharmaceutical → I-131: breastfeeding is stopped completely.

Data types: nominal (frequency/ratio), ordinal (median), quantitative (mean ± SD)

Correlation |r|: 0.4-0.6 moderate, 0.6-0.8 high, >0.8 very high; correlation ≠ agreement (Bland-Altman)

Survival: censored data, Kaplan-Meier, log-rank/Wald test