Gamma Camera and SPECT/CT
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Solve questions (26) →Contents
- 6.1 Gamma Camera Components (Collimator, Crystal, PMT)
- 6.1.1 General Structure and Principle of Operation
- 6.1.2 Collimator
- 6.1.3 NaI(Tl) Scintillation Crystal
- 6.1.4 Light Guide
- 6.1.5 Photomultiplier Tubes (PMT)
- 6.1.6 Position Circuitry (Anger Logic)
- 6.1.7 Pulse Height Analyser (PHA) and Energy Window
- 6.2 Collimator Types and Selection
- 6.2.1 Parallel-Hole Collimators
- 6.2.2 Pinhole Collimator
- 6.2.3 Converging Collimator
- 6.2.4 Diverging Collimator
- 6.2.5 Collimator Types – Comparative Summary
- 6.3 Energy Window and Pulse Height Analyser
- 6.3.1 Role of the PHA in the Gamma Camera
- 6.3.2 Single and Multiple Energy Windows
- 6.3.3 Scatter Correction Windows
- 6.4 SPECT Principle and Acquisition
- 6.4.1 Basic Principle of SPECT
- 6.4.2 SPECT Acquisition Parameters
- 6.4.3 SPECT Reconstruction
- 6.4.4 SPECT Image Orientation
- 6.5 SPECT/CT Hybrid Imaging
- 6.5.1 Basic Principle of SPECT/CT
- 6.5.2 The CT Component of SPECT/CT
- 6.5.3 SPECT/CT Registration and Artefacts
- 6.5.4 Clinical Applications of SPECT/CT
- 6.5.5 Quantitative SPECT/CT and Patient-Specific Dosimetry
- 6.6 Gamma Camera Performance Parameters
- 6.6.1 Spatial Resolution
- 6.6.2 Sensitivity
- 6.6.3 Uniformity
- 6.6.4 Energy Resolution
- 6.6.5 Count Rate Performance
- 6.6.6 Spatial Linearity
- 6.6.7 Performance Parameters Summary Table
- Key Points for the Board
- Current guidelines on this chapter's topics
Learning objectives and modules3 modules · about 2 h 30 min
Learning objectives
After this chapter you will be able to:
- Explain the components of the gamma camera and how Anger logic determines position and energy.
- Compare collimator types; select a collimator by energy and study type and explain the resolution–sensitivity trade-off.
- Explain the role of the energy window and pulse height analysis in reducing scatter.
- Select SPECT acquisition parameters (orbit, arc, number of projections, matrix) for the study type.
- Explain the role of CT in attenuation correction and localisation in SPECT/CT and the artefacts it may cause.
- Define the performance parameters of the gamma camera (resolution, uniformity, energy resolution, dead time).
Modules
The chapter is divided into study modules without changing the order of the text: read, watch the animations, then answer the questions linked to those headings.
- Module 16.1–6.2 Gamma Camera Components (Collimator, Crystal, PMT) · Collimator Types and Selection1 h · 3 animations · 22 questionsAnswer the questions →
- Module 26.3–6.5 Energy Window and Pulse Height Analyser · SPECT Principle and Acquisition · SPECT/CT Hybrid Imaging55 min · 2 animations · 21 questionsAnswer the questions →
- Module 36.6 Gamma Camera Performance Parameters · Key Points for the Board35 min · 1 animation · 10 questionsAnswer the questions →
Times are estimates: 130 words per minute, 3 min per animation, 1.5 min per question.
MOST FREQUENTLY ASKED IN THIS CHAPTER
6.1 Gamma Camera Components (Collimator, Crystal, PMT)
6.1.1 General Structure and Principle of Operation
The gamma camera (Anger camera) is the device developed by Hal Anger in 1958 that forms the basis of planar and SPECT imaging in nuclear medicine. By detecting the gamma photons emitted from the patient, it produces a two-dimensional (planar) or three-dimensional (SPECT) map of radionuclide distribution.
Basic components (in order from outside to inside):
1. Collimator → selection of direction (passes only photons at a certain angle) 2. NaI(Tl) scintillation crystal → converts the gamma photon into light photons 3. Light guide → directs the light to the PMTs 4. Photomultiplier tubes (PMT) → convert light photons into an electrical signal 5. Position circuitry → determines the X, Y coordinates (Anger logic) 6. Pulse height analyser (PHA) → energy selection (rejects scattered photons) 7. Computer and image processing system → image formation and analysis
Signal flow:
Gamma photon → passage through the collimator → scintillation in the crystal (light production) → transmission through the light guide to the PMTs → conversion to an electrical signal in the PMTs → position calculation (X, Y) → energy analysis (Z pulse) → recording in the image matrix
Figure 6.1: Gamma camera components and signal flow: from the collimator to the image matrix (schematic).
6.1.2 Collimator
The collimator is the first and most critical component of the gamma camera. It provides spatial information by allowing only photons from certain directions to reach the crystal. Without a collimator photons reach the crystal from every direction and no meaningful image can be formed.
Structure:
Role of the collimator:
→ The COLLIMATOR.
→ Again the COLLIMATOR. The collimator determines both resolution and sensitivity, and there is an inverse relationship between the two. The collimator is chosen according to the clinical application! Collimator details are covered in Section 6.2.
6.1.3 NaI(Tl) Scintillation Crystal3 questions
The detector component of the gamma camera. It converts gamma photons into visible light photons (scintillation).
Physical properties (see Section 5.2 – detailed):
Effects of crystal thickness:
→ 3/8 inch (~9.5 mm).
→ It gives the optimal balance between sensitivity and resolution for the 140 keV photons of Tc-99m.
→ Sensitivity↑, intrinsic resolution↓.
→ Sensitivity↓, intrinsic resolution↑.
In a gamma camera the scintillation light spreads to the PMTs, position is found by a weighted mean and energy by the summed signal; the fraction of photons absorbed and the light spread by crystal thickness are shown.
Key point: the weighted mean of the PMT signals gives the position and their sum the energy; a thick crystal catches more photons but spreads the light wider, so the position becomes less certain.
Source: book (NaI(Tl) 3/8 inch, 3.67 g/cm³; X = Σ(Xᵢ·Sᵢ)/ΣSᵢ, Z = ΣSᵢ; Tc-99m window 126–154 keV). Absorption from the NIST XCOM NaI total attenuation coefficient (coherent included); the book's ~30% at 364 keV is the photopeak efficiency, as part of the interacting photons escape by Compton scattering. In the crystal-thickness step the side view is drawn at 2× vertical scale (light guide 12 mm). Light spot: point light source, reflections ignored, FWHM ≈ 1.53 × distance to the PMT plane. Model assumptions: 37 PMTs, 76 mm pitch, 12 mm light guide, ~930 photoelectrons at 140 keV, Poisson noise; PMTs below 10% of the largest signal ignored (like the threshold in modern cameras); scattered photons ~25% of events, 95–125 keV (illustrative).
How to use: a single click on the drawing pauses and resumes; in the crystal thickness step ↑ ↓ change the thickness, the buttons below change thickness and energy; ← → change steps.
Figure 6.2: Effect of crystal thickness on light spread, intrinsic resolution and photon absorption fraction.
Signs of crystal damage:
6.1.4 Light Guide
The optical coupling element located between the crystal and the PMTs.
Features:
6.1.5 Photomultiplier Tubes (PMT)
PMTs are vacuum tubes that convert the light photons from the crystal into an electrical signal and amplify it (see Section 5.2 – detailed).
PMT arrangement in the gamma camera:
Functions of the PMT in the gamma camera:
1. Position determination: The signal size from each PMT is used to calculate the location of the scintillation point
2. Energy determination: The sum of all PMT signals (Z pulse) gives the energy of the photon
6.1.6 Position Circuitry (Anger Logic)2 questions
The positioning logic developed by Hal Anger determines the X, Y coordinates of the scintillation event in the crystal.
Principle of operation:
Z pulse (energy signal):
→ Anger logic: the X, Y coordinates are calculated from the weighted mean of the signals from each PMT.
→ The sum of all PMT signals → represents the energy of the photon.
→ Intrinsic spatial resolution improves (more precise position calculation).
In a gamma camera the scintillation light spreads to the PMTs, position is found by a weighted mean and energy by the summed signal; the fraction of photons absorbed and the light spread by crystal thickness are shown.
Key point: the weighted mean of the PMT signals gives the position and their sum the energy; a thick crystal catches more photons but spreads the light wider, so the position becomes less certain.
Source: book (NaI(Tl) 3/8 inch, 3.67 g/cm³; X = Σ(Xᵢ·Sᵢ)/ΣSᵢ, Z = ΣSᵢ; Tc-99m window 126–154 keV). Absorption from the NIST XCOM NaI total attenuation coefficient (coherent included); the book's ~30% at 364 keV is the photopeak efficiency, as part of the interacting photons escape by Compton scattering. In the crystal-thickness step the side view is drawn at 2× vertical scale (light guide 12 mm). Light spot: point light source, reflections ignored, FWHM ≈ 1.53 × distance to the PMT plane. Model assumptions: 37 PMTs, 76 mm pitch, 12 mm light guide, ~930 photoelectrons at 140 keV, Poisson noise; PMTs below 10% of the largest signal ignored (like the threshold in modern cameras); scattered photons ~25% of events, 95–125 keV (illustrative).
How to use: a single click on the drawing pauses and resumes; in the crystal thickness step ↑ ↓ change the thickness, the buttons below change thickness and energy; ← → change steps.
Figure 6.3: Anger logic: determination of position (X, Y) from the weighted mean of the PMT signals and of energy (Z) from their sum (schematic).
6.1.7 Pulse Height Analyser (PHA) and Energy Window
The PHA accepts or rejects events according to the size of the Z pulse (see Section 5.5.3 – detailed). In the gamma camera the energy window setting is critical for image quality.
Standard energy window settings:
Effect of the energy window on image quality:
6.2 Collimator Types and Selection
6.2.1 Parallel-Hole Collimators9 questions
The most widely used type of collimator. All holes are parallel to one another and perpendicular to the crystal surface.
Features:
Subtypes of parallel-hole collimator:
1. Low Energy High Resolution (LEHR):
2. Low Energy All Purpose (LEAP) / Low Energy General Purpose (LEGP):
3. Low Energy High Sensitivity (LEHS):
4. Medium Energy (ME):
5. High Energy (HE):
→ LEHR or LEAP.
→ ME.
→ HE.
Figure 6.4: Subtypes of parallel-hole collimator: effect of hole length, diameter and septal thickness on sensitivity and resolution (schematic).
Design parameters of the parallel-hole collimator:
Collimator resolution formula (parallel-hole):
Rc = d × (L + z) / L
WHY IT MATTERS · Septal penetration criterion
See the animation: Figure 6.5 →
6.2.2 Pinhole Collimator4 questions
A collimator type consisting of a single small hole (aperture). It works on the principle of the camera obscura.
Features:
Clinical use:
Pinhole collimator aperture size:
→ INVERTED (left-right and top-bottom).
→ Thyroid scintigraphy.
→ When the object is close to the focal point. A thyroid scintigraphy image may be shown in the board exam with the question "which collimator was used?" → Pinhole (clue: inverted image).
6.2.3 Converging Collimator2 questions
The holes are angled so that they converge to a point in front of the crystal surface (fan-beam or cone-beam).
Features:
Clinical use:
6.2.4 Diverging Collimator
The holes are angled so that they diverge away from the crystal surface.
Features:
Clinical use (historical):
6.2.5 Collimator Types – Comparative Summary2 questions
→ Pinhole and converging.
→ Diverging.
→ Parallel-hole.
→ Pinhole.
Photons from an object are selected by the collimator and those passing form the image in the crystal; parallel-hole, pinhole, converging and diverging collimators and the effect of source–collimator distance are shown.
Key point: the collimator sets the image geometry; with a parallel-hole collimator resolution worsens with distance while sensitivity stays the same; a pinhole inverts the image and magnifies nearby objects.
Source: book; LEHR d = 1.5 mm, L = 35 mm (manufacturer value), Ri = 3.5 mm; Rc = d·(L + z)/L, Rs = √(Ri² + Rc²); pinhole M = f/z, f = 20 cm example value. Photon numbers and angles not to scale. Septa step: LEHR 1.5 / 0.2 / 35 mm and MEGP 3.0 / 1.05 / 58 mm (GE Discovery; Wright et al., Phys Med Biol 2017), HE 4.0 / 2.0 / 59.7 mm (Siemens Symbia); lead attenuation coefficients from NIST XCOM. This is a 2D cross-section simulation; true (3D) penetration fractions differ (Monte Carlo: LEHR + I-131 ~50%, HEGP + I-131 ~18%; Sawant et al., J Nucl Med Technol 2025).
How to use: a single click on the drawing pauses and resumes; in the distance steps drag the object or use ← → to move it closer or farther; in the septa step ↑ ↓ change the radionuclide.
Figure 6.5: Collimator types and their effect on image magnification/minification and inversion (schematic).
6.3 Energy Window and Pulse Height Analyser
6.3.1 Role of the PHA in the Gamma Camera
The PHA (pulse height analyser) performs energy selection in the gamma camera, rejecting scattered photons and increasing image contrast (see Section 5.5.3 – basic principles).
Function of the PHA in the gamma camera:
6.3.2 Single and Multiple Energy Windows
Single-window applications:
Multiple-window applications:
Dual-isotope studies:
6.3.3 Scatter Correction Windows
Additional energy windows can be used to estimate and correct scatter:
Triple Energy Window (TEW) method:
→ 3 windows (93, 185, 300 keV).
→ 2 windows (171, 245 keV).
→ 2 windows (70 keV and 167 keV). Using multiple windows increases sensitivity but makes scatter management more difficult.
Figure 6.6: Tc-99m photopeak window and triple energy window (TEW) scatter correction; radionuclides using multiple windows (schematic).
6.4 SPECT Principle and Acquisition
6.4.1 Basic Principle of SPECT2 questions
SPECT (Single Photon Emission Computed Tomography) works on the principle that the gamma camera rotates around the patient, collecting projection images from different angles, and three-dimensional (3D) tomographic images are formed from these projections.
Planar imaging vs SPECT:
SPECT vs PET comparison:
SPECT system geometries:
6.4.2 SPECT Acquisition Parameters6 questions
Detector configuration:
Rotation angle:
Number of projections (stops):
Time per projection:
Matrix size:
Rotation type:
Detector orbit:
→ 180° (RAO 45° → LPO 45°).
→ Attenuation in the posterior projections is very high → it degrades image quality.
→ 90° (L-mode) dual-head.
→ 360°.
→ The detector-patient distance is minimised → resolution is optimised.
Gamma camera heads rotating around a thoracic cross-section: 180° opposed and L-mode configurations, the angles acquired, and system resolution on circular and body-contour orbits are shown.
Key point: two opposed heads collect 360° of data in a 180° rotation; in cardiac imaging L-mode covers only the anterior 180° near the heart; a body-contour orbit keeps the detector close to the patient and preserves resolution.
Source: book (dual head 180°/90°, cardiac RAO 45° → LPO 45°, 60–128 projections over 360° and 32–64 for cardiac, 15–40 s per projection). Example: 128 and 64 projections, 20 s per projection, rotation time excluded. Body section 36 × 24 cm (illustrative), collimator 1.5 cm from the body. Resolution with the LEHR values of the collimator animation: Rc = d·(L + z)/L, Rs = √(Ri² + Rc²) (d 1.5 mm, L 35 mm, Ri 3.5 mm). Drawing to scale; heads with 40 cm field of view.
How to use: a single click on the drawing pauses and resumes; in the orbit step ↑ ↓ switch between the circular and the body-contour orbit; ← → change steps.
Figure 6.7: SPECT acquisition: 180° opposed and 90° (L-mode) detector configurations, with circular and body-contour orbits (schematic).
6.4.3 SPECT Reconstruction
SPECT reconstruction is the process of forming tomographic slice images from the acquired projection data (see Chapter 8 – detailed).
Basic methods:
Corrections in SPECT:
6.4.4 SPECT Image Orientation
Cardiac SPECT slice planes:
General SPECT slice planes:
→ Short axis (SA), vertical long axis (VLA), horizontal long axis (HLA). These planes are reoriented according to the anatomical axis of the heart (reorientation). A slice image may be shown in the board exam with the question "which plane?".
A 3D model of the left ventricle: the oblique appearance of transaxial slices due to the tilted long axis, reorientation by two angles, and SA, VLA and HLA slices are shown.
Key point: the heart's long axis is oblique to the body axes, so transaxial slices cut the left ventricle obliquely; the data are reoriented to the long axis and SA, VLA and HLA slices are taken relative to it.
Source: book (SA perpendicular to the long axis, ring; VLA sagittal, 2-chamber; HLA coronal, 4-chamber; reorientation). Model: left ventricle as a half-ellipsoid shell, illustrative adult dimensions (outer radius 3.4 cm, base to apex 8.5 cm, wall ~1.1 cm); the long axis points ~45° left of the sagittal plane and ~30° below the horizontal (illustrative, varies between patients). Right ventricle and atria not drawn. Slices computed from the model; colour shows tracer uptake.
How to use: a single click on the drawing pauses and resumes; in the third step ↑ ↓ change the slice plane (SA / VLA / HLA); ← → change steps.
Figure 6.8: Cardiac SPECT slice planes: short axis (SA), vertical long axis (VLA) and horizontal long axis (HLA) (schematic).
6.5 SPECT/CT Hybrid Imaging
6.5.1 Basic Principle of SPECT/CT2 questions
SPECT/CT is a hybrid imaging system in which a SPECT gamma camera and a diagnostic or low-dose CT are integrated on the same gantry. SPECT provides functional information, while CT provides anatomical information and an attenuation correction map.
Advantages of SPECT/CT:
1. Anatomical localisation: Determines the exact anatomical location of SPECT findings 2. CT-based attenuation correction (CTAC): More accurate quantitative assessment 3. Increased diagnostic confidence: Distinction between physiological and pathological uptake 4. Fewer false positives: Specificity increases with anatomical correlation 5. Fewer false negatives: Sensitivity increases with attenuation correction
History:
6.5.2 The CT Component of SPECT/CT3 questions
Types of CT:
SPECT/CT radiation dose:
Principle of CT attenuation correction (CTAC):
→ 1) Anatomical localisation, 2) Attenuation correction (CTAC).
→ The HU values obtained from CT are converted into attenuation coefficients appropriate to the SPECT photon energy → an attenuation map is created → used in SPECT reconstruction.
6.5.3 SPECT/CT Registration and Artefacts6 questions
Registration:
Artefacts specific to SPECT/CT:
Other causes of misregistration and artefacts:
6.5.4 Clinical Applications of SPECT/CT
Main indications:
→ Anatomical localisation and attenuation correction.
→ Streak artefact on CT → falsely high HU → overcorrection for attenuation → spurious hot artefact on SPECT.
→ Yes, by the same mechanism → overcorrection for attenuation → hot artefact. Solution: use non-contrast CT or acquire the CT before contrast.
Figure 6.9: The CT-based attenuation correction chain and the mechanisms of SPECT/CT artefacts (schematic).
6.5.5 Quantitative SPECT/CT and Patient-Specific Dosimetry2 questions
When attenuation, scatter and resolution corrections are applied, activity concentration (Bq/mL) can be measured with SPECT/CT and dosimetry can be performed in radionuclide therapies.
Volume definition and partial volume:
Patient-specific dosimetry:
6.6 Gamma Camera Performance Parameters
6.6.1 Spatial Resolution2 questions
Spatial resolution is the ability to distinguish two close points from each other. It is measured as the FWHM (full width at half maximum). Smaller FWHM = better resolution.
Components of spatial resolution:
1. Intrinsic resolution (Rᵢ):
2. Collimator resolution (Rc):
3. Total (system) resolution (Rₛ):
Rs = √(Rᵢ² + Rc²)
Methods of measuring spatial resolution:
→ The COLLIMATOR (Rc is usually much larger than Rᵢ).
→ Rs = √(Rᵢ² + Rc²).
→ Thin crystal, more/smaller PMTs.
→ Long/narrow holes, short distance.
6.6.2 Sensitivity
Sensitivity is the parameter showing what fraction of the photons emitted by the source is detected. It is expressed in cps/MBq or cps/µCi.
Factors affecting sensitivity:
Photons from an object are selected by the collimator and those passing form the image in the crystal; parallel-hole, pinhole, converging and diverging collimators and the effect of source–collimator distance are shown.
Key point: the collimator sets the image geometry; with a parallel-hole collimator resolution worsens with distance while sensitivity stays the same; a pinhole inverts the image and magnifies nearby objects.
Source: book; LEHR d = 1.5 mm, L = 35 mm (manufacturer value), Ri = 3.5 mm; Rc = d·(L + z)/L, Rs = √(Ri² + Rc²); pinhole M = f/z, f = 20 cm example value. Photon numbers and angles not to scale. Septa step: LEHR 1.5 / 0.2 / 35 mm and MEGP 3.0 / 1.05 / 58 mm (GE Discovery; Wright et al., Phys Med Biol 2017), HE 4.0 / 2.0 / 59.7 mm (Siemens Symbia); lead attenuation coefficients from NIST XCOM. This is a 2D cross-section simulation; true (3D) penetration fractions differ (Monte Carlo: LEHR + I-131 ~50%, HEGP + I-131 ~18%; Sawant et al., J Nucl Med Technol 2025).
How to use: a single click on the drawing pauses and resumes; in the distance steps drag the object or use ← → to move it closer or farther; in the septa step ↑ ↓ change the radionuclide.
Figure 6.10: Effect of source–collimator distance on system resolution and sensitivity (parallel-hole and pinhole collimators).
Sensitivity-resolution relationship:
6.6.3 Uniformity5 questions
Uniformity is the ability of the gamma camera to respond equally over its entire surface to a homogeneous radioactive source. It is the most important daily quality control parameter of the gamma camera.
Types of uniformity:
Uniformity measurement parameters:
Acceptable values (NEMA standards):
Causes of non-uniformity:
→ UNIFORMITY.
→ The collimator is REMOVED and a point source (Tc-99m) is used.
→ The collimator is FITTED and a flood source is used.
→ PMT gain drift.
6.6.4 Energy Resolution
Energy resolution is the ability of the gamma camera to distinguish photons of different energies from one another (see Section 5.5.2 – detailed).
Energy resolution in the gamma camera:
Factors affecting energy resolution:
6.6.5 Count Rate Performance1 questions
The ability of the gamma camera to work accurately at high count rates.
Dead time and count loss:
Count rate performance parameters:
High count rate situations:
Figure 6.11: Relationship between true and observed count rate in the gamma camera as a paralysable system; the 20% loss point.
6.6.6 Spatial Linearity2 questions
Spatial linearity is the ability of the gamma camera to image a straight line as straight.
Measurement method:
Causes of non-linearity:
Correction:
→ FIRST energy correction → THEN linearity correction → LAST uniformity correction. This order matters because energy and position errors are carried into the uniformity map. If uniformity is corrected before linearity → an artefact appears.
Figure 6.12: Order in which corrections are applied in the gamma camera: energy, linearity and uniformity (schematic).
6.6.7 Performance Parameters Summary Table
Key Points for the Board
SPECT/CT – Additional Points
Gamma Camera Components – Key Points to Memorise
Energy analysis (Z pulse) → Image
Collimator Selection – Quick Decision Table
Collimator Comparison – Critical Differences
Collimator Resolution Formula (Memorise!)
Rc = d × (L + z) / L
Total Resolution Formula (Memorise!)
Rs = √(Rᵢ² + Rc²)
SPECT Acquisition – Critical Parameters
SPECT/CT – Critical Points
Performance Parameters – Critical Points to Memorise
Energy Window – Quick Reference
Crystal Thickness – Table of Effects
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
Current guidelines on this chapter's topics
The latest guidelines and consensus documents on the procedures covered in this chapter (official EANM index and primary sources, November 2026). Comparison of the text with these versions is in progress; consult the guideline itself for details.
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