Q.1 What type of radiation is primarily detected by a SPECT camera?
Alpha particles
Beta particles
Gamma photons
X‑rays
Explanation - SPECT (Single Photon Emission Computed Tomography) uses radiopharmaceuticals that emit single gamma photons, which are detected by the gamma camera.
Correct answer is: Gamma photons
Q.2 Which component of the SPECT system determines the spatial resolution by allowing only photons traveling in certain directions to reach the detector?
Scintillation crystal
Photomultiplier tube
Collimator
Data acquisition computer
Explanation - The collimator is a grid of holes that filters incoming photons based on angle, directly affecting the system's spatial resolution.
Correct answer is: Collimator
Q.3 In a parallel‑hole collimator, decreasing the hole diameter while keeping hole length constant will:
Increase sensitivity and decrease resolution
Increase both sensitivity and resolution
Decrease sensitivity and increase resolution
Decrease both sensitivity and resolution
Explanation - Smaller holes admit fewer photons (lower sensitivity) but restrict angles more tightly, improving spatial resolution.
Correct answer is: Decrease sensitivity and increase resolution
Q.4 Which scintillation material is most commonly used in modern SPECT detectors?
NaI(Tl)
CsI(Tl)
BGO
LYSO
Explanation - Sodium Iodide doped with thallium (NaI(Tl)) has high light output and is the standard scintillator for gamma cameras in SPECT.
Correct answer is: NaI(Tl)
Q.5 The half‑life of Technetium‑99m, the most widely used SPECT radionuclide, is:
6 minutes
6 hours
6 days
6 weeks
Explanation - Tc‑99m has a 6‑hour half‑life, providing a good balance between imaging time and patient radiation dose.
Correct answer is: 6 hours
Q.6 Which reconstruction algorithm is most commonly employed for SPECT image formation?
Filtered Back Projection (FBP)
Maximum Likelihood Expectation Maximization (MLEM)
Fourier Transform
Radon Transform
Explanation - FBP is the traditional and still widely used reconstruction method for SPECT due to its speed, though iterative methods like MLEM are gaining popularity.
Correct answer is: Filtered Back Projection (FBP)
Q.7 Attenuation correction in SPECT is performed to:
Increase detector sensitivity
Compensate for photon loss due to tissue absorption
Reduce the half‑life of the radiopharmaceutical
Enhance collimator resolution
Explanation - Photons are absorbed or scattered by body tissues; attenuation correction algorithms adjust the measured counts to account for this loss, improving quantitative accuracy.
Correct answer is: Compensate for photon loss due to tissue absorption
Q.8 Which of the following isotopes is NOT suitable for SPECT imaging?
Iodine‑123
Fluorine‑18
Thallium‑201
Indium‑111
Explanation - Fluorine‑18 emits positrons and is used for PET, not SPECT, which requires single‑photon emitters.
Correct answer is: Fluorine‑18
Q.9 What is the primary advantage of a fan‑beam collimator over a parallel‑hole collimator?
Higher sensitivity for a given resolution
Simpler mechanical design
Better energy resolution
Reduced need for attenuation correction
Explanation - Fan‑beam collimators collect more photons from the same area, increasing sensitivity while maintaining spatial resolution comparable to parallel‑hole designs.
Correct answer is: Higher sensitivity for a given resolution
Q.10 In SPECT, the term "energy window" refers to:
The range of photon energies accepted by the detector
The time interval between two successive scans
The angular spread allowed by the collimator
The physical width of the detector crystal
Explanation - An energy window (e.g., 20% centered on 140 keV for Tc‑99m) filters out scattered photons, improving image contrast.
Correct answer is: The range of photon energies accepted by the detector
Q.11 Which of the following best describes the purpose of a septal thickness in a collimator?
To increase the number of detected photons
To block photons arriving at oblique angles
To provide mechanical support for the detector
To enhance the crystal’s light yield
Explanation - Septal walls separate adjacent holes and prevent photons that travel at undesired angles from reaching the detector, preserving resolution.
Correct answer is: To block photons arriving at oblique angles
Q.12 The term "sensitivity" in a SPECT system most directly refers to:
The ability to distinguish two close points
The fraction of emitted photons that are detected
The speed of image reconstruction
The accuracy of patient positioning
Explanation - Sensitivity is the proportion of emitted gamma photons that reach the detector and are recorded, influencing scan time and image quality.
Correct answer is: The fraction of emitted photons that are detected
Q.13 A SPECT scan of the brain using Iodine‑123‑IMP primarily evaluates:
Cerebral blood flow
Glucose metabolism
Amyloid plaque density
Dopamine receptor density
Explanation - I‑123‑IMP is a perfusion tracer that distributes proportionally to regional cerebral blood flow.
Correct answer is: Cerebral blood flow
Q.14 Which of the following best describes a “dual‑head” SPECT camera?
Two detectors positioned opposite each other to acquire data simultaneously
A detector that can operate at two different energy windows
A system that uses both PET and SPECT modalities
A camera with two interchangeable collimators
Explanation - Dual‑head systems have two gamma cameras mounted at 180°, allowing faster data acquisition and improved angular sampling.
Correct answer is: Two detectors positioned opposite each other to acquire data simultaneously
Q.15 Which physical effect is most responsible for the loss of spatial resolution with increasing distance from the collimator surface?
Photon attenuation
Scatter in the patient
Geometric blurring due to hole size
Electronic noise in the PMT
Explanation - As photons travel farther from the collimator, the angular uncertainty defined by the hole size translates into larger positional uncertainty on the detector.
Correct answer is: Geometric blurring due to hole size
Q.16 The term "count density" in a SPECT image refers to:
Number of photons detected per unit time per pixel
Energy of photons recorded by the detector
Physical thickness of the collimator septa
Voltage applied to the photomultiplier tubes
Explanation - Count density is the measured intensity (counts) in each image pixel, proportional to tracer concentration after corrections.
Correct answer is: Number of photons detected per unit time per pixel
Q.17 Which correction technique is used to compensate for the limited angular sampling of SPECT data?
Fourier filtering
Iterative reconstruction
Scatter correction
Resolution recovery
Explanation - Resolution recovery (also called point‑spread function modeling) compensates for the system’s blurring and limited angular sampling during reconstruction.
Correct answer is: Resolution recovery
Q.18 A common source of artifacts in SPECT images is patient motion. Which of the following is a typical method to reduce motion artifacts?
Increasing the energy window width
Using a high‑resolution collimator
Applying motion‑correction software
Shortening the radiopharmaceutical’s half‑life
Explanation - Software can align frames acquired over time, reducing blurring caused by patient movement during the scan.
Correct answer is: Applying motion‑correction software
Q.19 Which of the following is an advantage of using a pinhole collimator in small‑animal SPECT?
Higher sensitivity for large fields of view
Improved spatial resolution at the expense of sensitivity
Simplified reconstruction algorithms
Reduced need for attenuation correction
Explanation - Pinhole collimators magnify the image and provide high resolution, but only a small fraction of photons pass through the pinhole, lowering sensitivity.
Correct answer is: Improved spatial resolution at the expense of sensitivity
Q.20 In SPECT, the term "scatter fraction" quantifies:
The proportion of photons that are absorbed in the patient
The ratio of scattered photons to total detected photons
The percentage of dead time in the detector electronics
The fraction of photons that pass through the collimator septa
Explanation - Scatter fraction measures how many detected photons have changed direction and energy, degrading image contrast.
Correct answer is: The ratio of scattered photons to total detected photons
Q.21 Which of the following best describes the role of a photomultiplier tube (PMT) in a SPECT camera?
To convert gamma photons directly into electric charge
To amplify the light produced by the scintillation crystal
To focus gamma photons onto the detector surface
To filter out scattered photons
Explanation - The scintillation crystal converts gamma photons to visible light, and the PMT multiplies this light signal into an electrical pulse.
Correct answer is: To amplify the light produced by the scintillation crystal
Q.22 During SPECT acquisition, why is it common to acquire data over a 360° rotation of the detector?
To increase the energy resolution of the detector
To ensure uniform sampling of all projection angles
To reduce the half‑life of the radiopharmaceutical
To eliminate the need for collimators
Explanation - A full 360° rotation provides complete angular information, which is essential for accurate tomographic reconstruction.
Correct answer is: To ensure uniform sampling of all projection angles
Q.23 Which of the following is a quantitative measure that can be derived from SPECT images after proper calibration?
Standardized Uptake Value (SUV)
Hounsfield Unit (HU)
Brix parameter
T1 relaxation time
Explanation - SUV, widely used in PET, can also be calculated from SPECT data when attenuation, scatter, and calibration are applied, providing a semi‑quantitative metric of tracer uptake.
Correct answer is: Standardized Uptake Value (SUV)
Q.24 The most common cause of “edge artefact” (also called “ring artefact”) in SPECT images is:
Incorrect collimator alignment
Improper energy window setting
Failure to correct for attenuation
Non‑uniform detector response
Explanation - Variations in detector gain or crystal sensitivity cause artificial high‑intensity rings near the edges of the field of view.
Correct answer is: Non‑uniform detector response
Q.25 Which of the following statements about the “dead time” of a gamma camera is true?
It is the time required for the collimator to be cleaned between scans.
It is the period after each event during which the detector cannot record another event.
It is the interval needed for the radiopharmaceutical to reach equilibrium in the body.
It is the time taken for the reconstruction algorithm to finish.
Explanation - Dead time is the brief interval after a photon is detected when the system is busy processing the signal, leading to count losses at high rates.
Correct answer is: It is the period after each event during which the detector cannot record another event.
Q.26 In the context of SPECT, the term "orbit" refers to:
The path taken by the radiopharmaceutical in the bloodstream
The circular trajectory of the detector around the patient
The sequence of energy windows applied during acquisition
The algorithm used for image reconstruction
Explanation - An orbit is the set of angular positions the detector assumes as it rotates around the patient during data acquisition.
Correct answer is: The circular trajectory of the detector around the patient
Q.27 Which of the following is NOT a typical use of SPECT imaging?
Myocardial perfusion assessment
Brain dopamine transporter imaging
Bone density measurement
Renal cortical function evaluation
Explanation - Bone density is usually measured by DEXA (dual‑energy X‑ray absorptiometry), not SPECT.
Correct answer is: Bone density measurement
Q.28 What is the purpose of a “low‑energy high‑resolution” (LEHR) collimator?
To increase sensitivity for high‑energy photons
To provide the best possible spatial resolution for low‑energy isotopes
To reduce the need for attenuation correction
To enable simultaneous PET/SPECT imaging
Explanation - LEHR collimators have small holes and thin septa designed for low‑energy gamma emitters like Tc‑99m, maximizing resolution.
Correct answer is: To provide the best possible spatial resolution for low‑energy isotopes
Q.29 When performing quantitative SPECT for dosimetry, why is it important to know the exact administered activity?
Because it determines the scan duration
Because it is required for absolute activity concentration calculations
Because it affects the choice of collimator
Because it changes the photon energy
Explanation - Accurate knowledge of administered activity enables conversion of measured counts to absolute activity per volume, essential for dosimetry.
Correct answer is: Because it is required for absolute activity concentration calculations
Q.30 Which of the following best describes the principle of “list‑mode” data acquisition in SPECT?
Storing each detected photon’s position, energy, and time individually
Collecting data in a single summed projection image
Acquiring data only at one angle
Recording only photons that pass a narrow energy window
Explanation - List‑mode records each event separately, allowing flexible re‑binning and retrospective application of filters or windows.
Correct answer is: Storing each detected photon’s position, energy, and time individually
Q.31 A SPECT system has a spatial resolution of 8 mm at 10 cm from the collimator surface. If the object is moved to 20 cm distance, the expected resolution will be approximately:
4 mm
8 mm
16 mm
32 mm
Explanation - Resolution degrades roughly linearly with distance; doubling the distance roughly doubles the resolution value (blurs more).
Correct answer is: 16 mm
Q.32 Which of the following is a key difference between SPECT and PET?
SPECT uses positron emitters, PET uses gamma emitters
SPECT requires a collimator, PET does not
SPECT can provide quantitative data, PET cannot
PET uses rotating detectors, SPECT uses stationary detectors
Explanation - PET detects coincident annihilation photons directly, while SPECT relies on collimators to determine photon direction.
Correct answer is: SPECT requires a collimator, PET does not
Q.33 In SPECT, the term "uniformity" refers to:
Evenness of photon energy distribution across the detector
Consistent count rates across the field of view for a uniform source
Stability of the detector temperature during acquisition
Equal thickness of collimator septa
Explanation - Uniformity assesses whether the camera response is even; deviations indicate detector or collimator problems.
Correct answer is: Consistent count rates across the field of view for a uniform source
Q.34 Which of the following radiopharmaceuticals is most commonly used for myocardial perfusion SPECT?
Fluorodeoxyglucose (FDG)
Technetium‑99m sestamibi
Iodine‑131
Gallium‑67
Explanation - Tc‑99m sestamibi is a lipophilic tracer taken up by viable myocardium proportionally to blood flow.
Correct answer is: Technetium‑99m sestamibi
Q.35 Why is a high‑resolution collimator less sensitive than a low‑resolution collimator?
Because it has larger holes
Because it uses a thicker crystal
Because it has smaller holes and longer septa, letting fewer photons through
Because it operates at a higher voltage
Explanation - Tighter geometry improves resolution but reduces the solid angle for photon entry, decreasing sensitivity.
Correct answer is: Because it has smaller holes and longer septa, letting fewer photons through
Q.36 Which correction method is employed to address the effect of photon attenuation varying with tissue density?
CT‑based attenuation correction
Scatter window subtraction
Energy window broadening
Dead‑time correction
Explanation - Hybrid SPECT/CT systems acquire a low‑dose CT that provides attenuation maps for accurate correction.
Correct answer is: CT‑based attenuation correction
Q.37 In the context of SPECT, the term "projection" means:
A 3‑D reconstruction of the organ
A 2‑D image representing counts from a specific angle
The energy spectrum of detected photons
The physical layout of the collimator holes
Explanation - A projection is the raw data acquired at a particular detector angle before reconstruction.
Correct answer is: A 2‑D image representing counts from a specific angle
Q.38 The term "spill‑over“ in SPECT image quality refers to:
Counts from one organ leaking into an adjacent region due to limited resolution
Radioactive decay spilling over into neighboring isotopes
Energy spill‑over from high‑energy photons into the main window
Electrical spill‑over between adjacent PMT channels
Explanation - Partial volume effects cause activity from a high‑uptake region to appear in neighboring low‑uptake voxels.
Correct answer is: Counts from one organ leaking into an adjacent region due to limited resolution
Q.39 Which of the following describes a major limitation of using a high‑energy collimator for I‑131 imaging?
Insufficient sensitivity due to small hole size
Excessive septal penetration leading to image blurring
Incompatibility with NaI(Tl) crystals
Inability to apply energy windowing
Explanation - I‑131 emits high‑energy photons that can penetrate septa, reducing contrast and resolution despite using a high‑energy collimator.
Correct answer is: Excessive septal penetration leading to image blurring
Q.40 During SPECT image reconstruction, which step converts projection data into a volumetric image?
Filtering
Back‑projection
Fourier transformation
Segmentation
Explanation - Back‑projection distributes each projection’s counts back across the image space; when combined with filtering, it yields the final volume.
Correct answer is: Back‑projection
Q.41 Which of the following is a common method to reduce scatter in SPECT images?
Using a thicker collimator septa
Applying a dual‑energy window subtraction technique
Increasing the administered activity
Decreasing the detector temperature
Explanation - Scatter correction often uses a secondary energy window to estimate scattered photons and subtract them from the primary window.
Correct answer is: Applying a dual‑energy window subtraction technique
Q.42 What is the principal reason that SPECT imaging time is typically longer than PET for the same activity dose?
SPECT detectors have lower intrinsic efficiency
SPECT uses isotopes with longer half‑lives
SPECT requires a collimator which reduces photon count
SPECT images require higher resolution
Explanation - The collimator blocks most photons, lowering sensitivity, thus requiring longer acquisition times to achieve comparable counts.
Correct answer is: SPECT requires a collimator which reduces photon count
Q.43 In SPECT, the term “voxel” refers to:
A single photon detection event
A three‑dimensional pixel representing volume in the reconstructed image
A type of collimator
The energy window width
Explanation - A voxel is the 3‑D analog of a pixel, containing count density for a small region of the imaged volume.
Correct answer is: A three‑dimensional pixel representing volume in the reconstructed image
Q.44 Which of the following best explains why SPECT images can appear “noisy” at low count levels?
Increased photon energy
Statistical fluctuations (Poisson noise) in the detected counts
Higher detector voltage
Wider energy windows
Explanation - When count numbers are low, random variations become more pronounced, degrading image smoothness.
Correct answer is: Statistical fluctuations (Poisson noise) in the detected counts
Q.45 Which parameter is primarily altered when switching from a LEHR to a MEGP collimator for a high‑energy isotope?
Hole diameter
Septal thickness
Material composition of the crystal
Photomultiplier gain
Explanation - MEGP (medium‑energy general purpose) collimators have thicker septa to stop higher‑energy photons from penetrating.
Correct answer is: Septal thickness
Q.46 The main advantage of using iterative reconstruction (e.g., OSEM) over filtered back‑projection in SPECT is:
Faster computation time
Better handling of attenuation and scatter corrections
Elimination of the need for a collimator
Increased photon energy
Explanation - Iterative algorithms can incorporate physical models of attenuation, scatter, and resolution directly, improving image quality.
Correct answer is: Better handling of attenuation and scatter corrections
Q.47 When a SPECT system reports a “system sensitivity” of 800 cps/MBq, this means:
The detector records 800 counts per second for each megabecquerel of activity administered
The collimator has 800 holes per cm²
The reconstruction algorithm needs 800 iterations to converge
The patient receives 800 mSv of dose
Explanation - System sensitivity quantifies count rate per unit activity, reflecting overall detection efficiency.
Correct answer is: The detector records 800 counts per second for each megabecquerel of activity administered
Q.48 In a SPECT/CT hybrid system, the CT component primarily provides:
Higher energy photons for better resolution
Anatomical localization and attenuation maps
Additional radiotracer information
Time‑of‑flight data
Explanation - CT supplies high‑resolution anatomical images and attenuation coefficients for correction of the SPECT data.
Correct answer is: Anatomical localization and attenuation maps
Q.49 Which of the following is a typical clinical indication for using 123I‑Ioflupane (DaTSCAN) SPECT?
Evaluation of myocardial ischemia
Assessment of dopamine transporter density in Parkinsonian syndromes
Detection of bone metastases
Measurement of renal plasma flow
Explanation - I‑123‑Ioflupane binds to dopamine transporters, allowing visualization of nigrostriatal integrity.
Correct answer is: Assessment of dopamine transporter density in Parkinsonian syndromes
Q.50 The term “partial‑volume effect” in SPECT refers to:
Loss of counts due to photon attenuation
Blurring of small structures because their size is comparable to system resolution
Increase in dead time at high count rates
Energy spill‑over between windows
Explanation - When an object is smaller than the system’s spatial resolution, its measured activity is underestimated and appears spread out.
Correct answer is: Blurring of small structures because their size is comparable to system resolution
Q.51 A SPECT study performed with a 20% energy window centered at 140 keV for Tc‑99m will accept photons with energies ranging from:
112 keV to 168 keV
126 keV to 154 keV
130 keV to 150 keV
138 keV to 142 keV
Explanation - 20 % of 140 keV is 28 keV; half of that (±14 keV) gives the window limits 126–154 keV.
Correct answer is: 126 keV to 154 keV
Q.52 Which of the following is a major source of “septal penetration” artifacts in high‑energy SPECT imaging?
Thin collimator septa
Wide energy windows
Low detector temperature
High voltage on PMTs
Explanation - High‑energy photons can pass through thin septa, creating background counts and reducing contrast.
Correct answer is: Thin collimator septa
Q.53 When a SPECT acquisition uses 64 projections over 360°, the angular increment between consecutive projections is:
5.6°
2.8°
1.0°
0.5°
Explanation - 360° / 64 = 5.625°, rounded to 5.6° per projection.
Correct answer is: 5.6°
Q.54 In quantitative SPECT, the term “calibration factor” is used to:
Convert measured counts to activity concentration (kBq/mL)
Adjust the voltage of the PMTs
Set the collimator hole size
Define the energy window width
Explanation - A calibration factor, derived from a phantom with known activity, translates counts per voxel to absolute activity values.
Correct answer is: Convert measured counts to activity concentration (kBq/mL)
Q.55 Which of the following is a true statement about the relationship between photon energy and collimator design?
Higher‑energy photons require collimators with larger hole diameters and thicker septa.
Higher‑energy photons can be imaged with the same collimator as low‑energy photons without penalty.
Low‑energy photons need thicker septa than high‑energy photons.
Photon energy does not influence collimator choice.
Explanation - To avoid septal penetration and maintain sensitivity, high‑energy collimators have bigger holes and thicker walls.
Correct answer is: Higher‑energy photons require collimators with larger hole diameters and thicker septa.
Q.56 The primary reason why SPECT is often combined with CT rather than MRI is:
CT provides attenuation correction maps quickly and with low cost
MRI has higher radiation dose
CT detectors are more sensitive to gamma photons
MRI cannot be placed near a gamma camera
Explanation - CT offers fast, low‑dose, density‑based attenuation maps that are directly usable for SPECT correction, whereas MRI does not provide electron density information.
Correct answer is: CT provides attenuation correction maps quickly and with low cost
Q.57 Which of the following is NOT a typical step in the SPECT quality‑control (QC) routine?
Uniformity test
Energy resolution test
Spatial resolution test
Magnetic field mapping
Explanation - Magnetic field mapping is relevant to MRI QC, not SPECT.
Correct answer is: Magnetic field mapping
Q.58 A SPECT image shows a uniform hot spot in the liver due to radiotracer uptake. To quantify the liver activity, which region‑of‑interest (ROI) technique is most appropriate?
Single‑pixel ROI
Whole‑body ROI
Volume‑of‑interest (VOI) encompassing the liver
Background ROI only
Explanation - A VOI that matches the organ volume provides an averaged count density, reducing noise and allowing accurate quantification.
Correct answer is: Volume‑of‑interest (VOI) encompassing the liver
Q.59 During SPECT acquisition, a “dead‑time correction” factor of 1.05 is applied. This indicates that:
The system lost 5 % of counts due to dead time
The detector temperature increased by 5 °C
The acquisition time was increased by 5 seconds
The energy window was widened by 5 keV
Explanation - A correction factor >1 compensates for count losses; 1.05 means the raw counts are multiplied by 1.05 to estimate true counts.
Correct answer is: The system lost 5 % of counts due to dead time
Q.60 Which of the following isotopes emits photons at an energy of approximately 364 keV and therefore requires a high‑energy collimator?
Technetium‑99m
Iodine‑123
Iodine‑131
Thallium‑201
Explanation - I‑131 emits a primary gamma photon at 364 keV, demanding a high‑energy collimator to avoid septal penetration.
Correct answer is: Iodine‑131
Q.61 In a SPECT study, the term “acquisition matrix” (e.g., 128 × 128) defines:
The number of detector elements in the crystal
The size of the collimator holes
The number of pixels in each projection image
The number of energy windows used
Explanation - The acquisition matrix sets the pixel dimensions of each 2‑D projection before reconstruction.
Correct answer is: The number of pixels in each projection image
Q.62 Which of the following statements about “list‑mode” acquisition is FALSE?
It allows flexible re‑binning of data after acquisition.
It records each photon event with its spatial, energy, and timing information.
It results in a single summed image after acquisition.
It can be used for motion‑correction algorithms.
Explanation - List‑mode stores individual events; a summed image is generated later if desired.
Correct answer is: It results in a single summed image after acquisition.
Q.63 When a SPECT system uses a “dual‑head” configuration, the effective acquisition time to obtain the same count statistics as a single‑head system is:
Approximately doubled
Approximately halved
Unchanged
Three times longer
Explanation - Two heads acquire data simultaneously, effectively doubling count rate and halving required scan time for the same statistics.
Correct answer is: Approximately halved
Q.64 In the context of SPECT, “spill‑over” is most closely related to which physical phenomenon?
Photon attenuation
Partial‑volume effect
Scatter
Dead time
Explanation - Spill‑over describes activity from a high‑uptake region appearing in adjacent voxels due to limited resolution.
Correct answer is: Partial‑volume effect
Q.65 A SPECT camera shows a uniformity test result of 3 % deviation. This is considered:
Excellent (acceptable)
Poor (needs service)
Average (borderline)
Irrelevant
Explanation - Uniformity deviations below 5 % are generally acceptable for clinical SPECT systems.
Correct answer is: Excellent (acceptable)
Q.66 Which of the following radiopharmaceuticals is specifically used for bone SPECT imaging?
Tc‑99m MDP (methylene diphosphonate)
F‑18 FDG
I‑123 ioflupane
Ga‑67 citrate
Explanation - Tc‑99m MDP binds to hydroxyapatite in bone, highlighting areas of increased turnover.
Correct answer is: Tc‑99m MDP (methylene diphosphonate)
Q.67 In a SPECT/CT study, why is it important to perform CT at the same patient position as the SPECT acquisition?
To ensure proper attenuation correction and anatomical registration
To increase the CT radiation dose
To calibrate the gamma camera
To reduce the SPECT scan time
Explanation - Misalignment would cause incorrect attenuation maps and inaccurate fusion of functional and anatomical images.
Correct answer is: To ensure proper attenuation correction and anatomical registration
Q.68 The term “dead‑time loss” becomes significant when:
The count rate exceeds the detector’s processing capability
The radiopharmaceutical has a very short half‑life
The collimator is too thick
The energy window is too narrow
Explanation - At high count rates, the detector cannot process each event instantly, resulting in lost counts.
Correct answer is: The count rate exceeds the detector’s processing capability
Q.69 What is the effect of increasing the number of iterations in an OSEM reconstruction on image quality?
Resolution improves but noise may increase
Sensitivity increases dramatically
Acquisition time becomes shorter
Energy resolution is enhanced
Explanation - More iterations better fit the data, sharpening edges, but also amplify statistical noise.
Correct answer is: Resolution improves but noise may increase
Q.70 In SPECT imaging of the thyroid, which radiopharmaceutical is most commonly used?
I‑123 sodium iodide
Tc‑99m sestamibi
Ga‑67 citrate
F‑18 fluorodeoxyglucose
Explanation - I‑123 is taken up by the thyroid gland, providing functional imaging of thyroid tissue.
Correct answer is: I‑123 sodium iodide
Q.71 Which of the following best explains why high‑energy collimators have lower spatial resolution compared to low‑energy collimators?
They use larger hole diameters to maintain sensitivity for higher‑energy photons.
They are made from lower‑density materials.
They have thinner septa.
They operate at lower voltage.
Explanation - To allow high‑energy photons to pass, holes must be larger, which reduces the angular selectivity and thus resolution.
Correct answer is: They use larger hole diameters to maintain sensitivity for higher‑energy photons.
Q.72 A SPECT scan is performed with a 128 × 128 matrix and a pixel size of 3.4 mm. What is the approximate field of view (FOV) covered in the reconstructed images?
≈ 4.3 cm
≈ 13.8 cm
≈ 21.8 cm
≈ 43.5 cm
Explanation - FOV = matrix size × pixel size = 128 × 3.4 mm ≈ 435 mm ≈ 43.5 cm.
Correct answer is: ≈ 43.5 cm
Q.73 Which of the following is a reason to use a “high‑resolution” (HR) collimator for brain SPECT?
To increase count sensitivity
To improve detection of small cortical structures
To reduce patient dose
To simplify attenuation correction
Explanation - HR collimators have finer geometry, yielding better spatial resolution needed for detailed brain imaging.
Correct answer is: To improve detection of small cortical structures
Q.74 In SPECT, the term “scatter correction” most commonly uses which method?
Dual‑energy window subtraction
Fourier filtering
Iterative reconstruction only
Physical collimator redesign
Explanation - A secondary energy window estimates scattered photon contribution and subtracts it from the primary window.
Correct answer is: Dual‑energy window subtraction
Q.75 Which of the following best describes a “dead‑time” of 200 ns in a gamma camera?
The detector cannot record another event for 200 nanoseconds after each photon is detected.
The collimator holes are closed for 200 ns each rotation.
The reconstruction algorithm pauses for 200 ns between iterations.
The PMT voltage is reduced for 200 ns after each count.
Explanation - Dead‑time is the processing interval during which the system is insensitive to new events.
Correct answer is: The detector cannot record another event for 200 nanoseconds after each photon is detected.
Q.76 When performing a SPECT study with a radiopharmaceutical that has a short half‑life, the most important consideration for scan timing is:
Acquiring data as early as possible after injection
Using the widest possible energy window
Employing a low‑resolution collimator
Increasing the number of projections
Explanation - Short‑lived tracers decay quickly, so early acquisition maximizes count statistics before activity diminishes.
Correct answer is: Acquiring data as early as possible after injection
Q.77 Which of the following is NOT a typical cause of image distortion in SPECT?
Patient motion
Collimator misalignment
Improper energy window selection
Magnetic resonance field strength
Explanation - Magnetic field strength is irrelevant to SPECT; it pertains to MRI.
Correct answer is: Magnetic resonance field strength
Q.78 In the context of SPECT, what does the abbreviation “MLEM” stand for?
Maximum Likelihood Expectation Maximization
Multi‑Level Energy Modulation
Matrix Linear Equation Method
Monte Carlo Light Emission Modeling
Explanation - MLEM is an iterative reconstruction algorithm that maximizes the likelihood of the measured data.
Correct answer is: Maximum Likelihood Expectation Maximization
Q.79 The main physical principle that enables a SPECT camera to form images of three‑dimensional distribution of a tracer is:
Magnetic resonance of hydrogen nuclei
Coincidence detection of annihilation photons
Rotational acquisition of 2‑D projections followed by tomographic reconstruction
Ultrasound wave reflection
Explanation - SPECT collects multiple 2‑D views around the patient and reconstructs them into a 3‑D volume.
Correct answer is: Rotational acquisition of 2‑D projections followed by tomographic reconstruction
Q.80 Which of the following is a typical application of SPECT in oncology?
Staging of lymphoma using Tc‑99m‑sulfur colloid
Detecting bone metastases with Tc‑99m MDP
Measuring tumor glucose metabolism with F‑18 FDG
Assessing brain perfusion in epilepsy
Explanation - Tc‑99m MDP bone scans are widely used to identify skeletal metastatic disease.
Correct answer is: Detecting bone metastases with Tc‑99m MDP
Q.81 A SPECT system with a system sensitivity of 600 cps/MBq and a collimator efficiency of 0.25 will detect approximately how many counts per second from a 5 MBq source (ignoring attenuation and scatter)?
750 cps
1500 cps
3000 cps
600 cps
Explanation - Effective count rate = sensitivity × source activity × collimator efficiency = 600 cps/MBq × 5 MBq × 0.25 = 750 cps.
Correct answer is: 750 cps
Q.82 Which of the following is the most accurate description of “energy resolution” for a NaI(Tl) detector?
The ability to distinguish photons of different energies, expressed as a percentage of the photopeak width
The speed at which the detector processes events
The spatial separation between two point sources
The number of holes per cm² in the collimator
Explanation - Energy resolution quantifies how sharply the detector can define the photopeak, influencing scatter rejection.
Correct answer is: The ability to distinguish photons of different energies, expressed as a percentage of the photopeak width
Q.83 When a SPECT image shows a “cold spot” (area of low counts) in a region that should have high uptake, the most likely cause is:
Attenuation artifact
Radiopharmaceutical over‑dose
High detector sensitivity
Excessive collimator thickness
Explanation - Dense structures (e.g., bone) can attenuate photons, causing apparent low‑count regions if not corrected.
Correct answer is: Attenuation artifact
Q.84 Which of the following SPECT tracers is primarily used for evaluating myocardial perfusion?
Tc‑99m tetrofosmin
I‑123 metaiodobenzylguanidine (MIBG)
Ga‑67 citrate
F‑18 flurpiridaz
Explanation - Tc‑99m tetrofosmin is a lipophilic perfusion agent used for cardiac SPECT stress‑rest studies.
Correct answer is: Tc‑99m tetrofosmin
Q.85 In SPECT, what is the primary advantage of a “circular orbit” over an “elliptical orbit” acquisition geometry?
More uniform sampling of projection angles
Reduced scan time
Higher detector sensitivity
Simpler patient positioning
Explanation - Circular orbits keep angular spacing constant, providing consistent coverage; elliptical orbits can lead to variable sampling density.
Correct answer is: More uniform sampling of projection angles
Q.86 The term “photon septal penetration” is most critical for which combination of isotope and collimator?
Tc‑99m with LEHR collimator
I‑131 with high‑energy collimator
I‑123 with MEGP collimator
Ga‑67 with low‑energy collimator
Explanation - I‑131 emits high‑energy photons that can pass through septa if the collimator is not thick enough, causing artifacts.
Correct answer is: I‑131 with high‑energy collimator
Q.87 In quantitative SPECT, the term “partial‑volume correction (PVC)” is applied to:
Adjust for differences in detector gain
Compensate for activity spill‑over from small structures
Correct for photon attenuation
Normalize counts to patient weight
Explanation - PVC algorithms estimate true activity in structures smaller than the system resolution, correcting for partial‑volume loss.
Correct answer is: Compensate for activity spill‑over from small structures
Q.88 When performing a brain SPECT scan with I‑123‑IMP, why is patient preparation often required to avoid interference from external light sources?
I‑123‑IMP is photosensitive and degrades in light
External light can affect the gamma camera’s PMTs
The patient’s eyes emit photons that confuse the detector
Light influences the energy window settings
Explanation - Strong ambient light can cause additional electrical noise in the photomultiplier tubes, degrading image quality.
Correct answer is: External light can affect the gamma camera’s PMTs
Q.89 Which of the following is a primary reason to use a “high‑sensitivity” collimator for a low‑dose pediatric SPECT study?
To reduce the required administered activity while maintaining image quality
To increase the spatial resolution beyond that of a high‑resolution collimator
To eliminate the need for attenuation correction
To allow the use of higher‑energy isotopes
Explanation - High‑sensitivity collimators collect more photons, enabling lower injected doses, which is critical for pediatric patients.
Correct answer is: To reduce the required administered activity while maintaining image quality
Q.90 In SPECT, a “count‑rate linearity test” is performed to verify:
That the detector response is proportional to activity over a range of count rates
That the energy resolution remains constant
That the collimator holes are uniformly spaced
That the patient positioning is repeatable
Explanation - Linearity ensures that the system accurately reflects changes in activity without saturation or dead‑time distortion.
Correct answer is: That the detector response is proportional to activity over a range of count rates
Q.91 Which of the following best describes the effect of “image smoothing” (e.g., Gaussian filter) on SPECT images?
Reduces noise at the cost of decreased spatial resolution
Increases sensitivity without changing noise
Improves attenuation correction accuracy
Eliminates the need for collimators
Explanation - Smoothing averages neighboring pixel values, lowering statistical noise but also blurring fine details.
Correct answer is: Reduces noise at the cost of decreased spatial resolution
Q.92 When a SPECT system reports a “system uniformity” of 2 % in the center of the field of view and 7 % at the periphery, what action is most appropriate?
Perform a detector gain calibration to improve peripheral uniformity
Replace the collimator immediately
Increase the administered activity
Ignore, as the overall uniformity is within acceptable limits
Explanation - Non‑uniform peripheral response can often be corrected by adjusting detector gain or performing a uniformity correction routine.
Correct answer is: Perform a detector gain calibration to improve peripheral uniformity
Q.93 Which of the following is NOT a typical characteristic of a “low‑energy high‑resolution” (LEHR) collimator?
Small hole diameter
Thin septa
Designed for isotopes ≤ 200 keV
High sensitivity for high‑energy photons
Explanation - LEHR collimators are optimized for low‑energy photons; they have low sensitivity for high‑energy isotopes.
Correct answer is: High sensitivity for high‑energy photons
Q.94 During a SPECT acquisition, the technician notices that the count rate drops sharply after 5 minutes. The most likely cause is:
Rapid decay of the radiopharmaceutical
Collimator misalignment
Increase in dead‑time
Failure of the energy window settings
Explanation - If the tracer has a short half‑life, activity decreases quickly, reducing count rate.
Correct answer is: Rapid decay of the radiopharmaceutical
Q.95 In the context of SPECT, what does the acronym “CTAC” stand for?
Computed Tomography Attenuation Correction
Continuous Time Acquisition Control
Collimator Transmission Alignment Calibration
Crystal Temperature Auto‑Compensation
Explanation - CTAC uses the CT data to generate attenuation maps for correcting SPECT counts.
Correct answer is: Computed Tomography Attenuation Correction
Q.96 Which of the following is the most important factor governing the choice of collimator for a given radionuclide?
Photon energy of the radionuclide
Patient weight
Acquisition time
Reconstruction algorithm
Explanation - Collimator design (hole size, septal thickness) must match the photon energy to prevent penetration and optimize resolution.
Correct answer is: Photon energy of the radionuclide
Q.97 For a SPECT system, the term “sensitivity” is typically expressed in:
cps/MBq
mm
keV
Hz
Explanation - Sensitivity is measured as counts per second detected per unit activity (megabecquerel).
Correct answer is: cps/MBq
Q.98 In a dual‑head SPECT system, if each head has a sensitivity of 400 cps/MBq, what is the combined system sensitivity (assuming no overlap)?
400 cps/MBq
800 cps/MBq
200 cps/MBq
1200 cps/MBq
Explanation - Sensitivities add for independent detectors; total = 400 + 400 = 800 cps/MBq.
Correct answer is: 800 cps/MBq
Q.99 Which of the following best describes why SPECT images are often displayed in a “rainbow” colour scale?
Rainbow scales enhance visual contrast for clinical interpretation
They correspond directly to photon energies
They reduce the need for attenuation correction
They are required for regulatory approval
Explanation - Colour maps improve the perception of subtle intensity differences, aiding diagnosis.
Correct answer is: Rainbow scales enhance visual contrast for clinical interpretation
Q.100 In SPECT, the term “slice thickness” refers to:
The physical thickness of the collimator plate
The reconstructed voxel dimension along the Z‑axis
The width of the energy window
The distance between two detector heads
Explanation - Slice thickness is the depth of each reconstructed image slab (voxel height).
Correct answer is: The reconstructed voxel dimension along the Z‑axis
Q.101 Which of the following is a typical clinical indication for a brain SPECT using 99mTc‑HMPAO?
Assessing cerebral perfusion in dementia
Measuring myocardial ejection fraction
Detecting hepatic metastases
Evaluating pulmonary embolism
Explanation - Tc‑99m‑HMPAO is a perfusion tracer used to evaluate cerebral blood flow, helpful in dementia work‑up.
Correct answer is: Assessing cerebral perfusion in dementia
Q.102 What is the most common cause of “septal penetration” artifacts in SPECT imaging of the thyroid with I‑123?
Using a low‑energy collimator with high‑energy photons
Patient motion during acquisition
Incorrect energy window selection
Insufficient detector cooling
Explanation - I‑123 emits photons at ~159 keV; a low‑energy collimator may not have thick enough septa, leading to penetration.
Correct answer is: Using a low‑energy collimator with high‑energy photons
Q.103 During a SPECT acquisition, a “frame” refers to:
A single projection at a specific angle
A subset of counts collected over a short time interval
A reconstructed slice of the 3‑D volume
A calibrated energy window
Explanation - Frames are used in list‑mode or gated acquisitions to segment data temporally.
Correct answer is: A subset of counts collected over a short time interval
Q.104 Which of the following best explains why SPECT images often have lower spatial resolution than PET images?
SPECT uses lower‑energy photons
SPECT employs collimators that limit photon acceptance
SPECT detectors have slower electronics
PET uses higher‑resolution crystals
Explanation - Collimators restrict photon angles, inherently reducing resolution compared to PET, which uses coincidence detection without collimators.
Correct answer is: SPECT employs collimators that limit photon acceptance
Q.105 In a SPECT study, why is it important to keep the patient’s arms away from the torso?
To reduce scatter from high‑attenuation tissues
To improve detector cooling
To avoid interfering with the CT component
To increase the administered activity
Explanation - Arms close to the torso increase photon attenuation and scatter, degrading image quality.
Correct answer is: To reduce scatter from high‑attenuation tissues
Q.106 Which of the following is a typical feature of a “high‑sensitivity” collimator compared to a “high‑resolution” collimator?
Larger hole diameter
Thinner septa
Longer hole length
Smaller field of view
Explanation - Larger holes increase photon acceptance, raising sensitivity at the expense of resolution.
Correct answer is: Larger hole diameter
Q.107 The main purpose of applying a “Gaussian filter” during SPECT image reconstruction is to:
Increase image contrast
Suppress high‑frequency noise
Correct for attenuation
Improve detector energy resolution
Explanation - A Gaussian filter smooths the image, reducing random noise while preserving overall structure.
Correct answer is: Suppress high‑frequency noise
Q.108 Which of the following isotopes is best suited for SPECT imaging of the adrenal glands due to its specific uptake mechanism?
I‑131 metaiodobenzylguanidine (MIBG)
Tc‑99m pertechnetate
F‑18 FDG
Ga‑68 DOTATATE
Explanation - MIBG is taken up by adrenergic tissue, making it useful for adrenal medulla imaging.
Correct answer is: I‑131 metaiodobenzylguanidine (MIBG)
Q.109 In a SPECT system, the term "energy window width" is typically expressed as:
Percentage of the photopeak energy
Absolute keV value
Number of detector channels
Degrees of angular coverage
Explanation - Energy windows are often set as a percent (e.g., 20 %) around the photopeak to include the main photon peak while excluding scatter.
Correct answer is: Percentage of the photopeak energy
Q.110 Which of the following best describes the function of a “lead‑shielded housing” for a SPECT camera?
To protect the detector from stray radiation and improve image quality
To increase the detector’s sensitivity
To cool the photomultiplier tubes
To focus gamma photons onto the crystal
Explanation - Lead shielding reduces background radiation and stray scatter reaching the detector.
Correct answer is: To protect the detector from stray radiation and improve image quality
Q.111 When a SPECT system uses a "step‑and‑shoot" acquisition mode, it means:
The detector rotates continuously while acquiring data.
The detector stops at each angle, acquires data, then moves to the next angle.
Data are collected only during patient breathing pauses.
The camera acquires data only after each radiopharmaceutical injection.
Explanation - Step‑and‑shoot acquires projections at discrete positions, allowing precise timing and gating.
Correct answer is: The detector stops at each angle, acquires data, then moves to the next angle.
Q.112 Which of the following is a primary advantage of using a “Monte Carlo simulation” in SPECT system design?
Accurate modeling of photon interactions and system response
Reducing the need for physical collimators
Eliminating dead‑time effects
Increasing the half‑life of isotopes
Explanation - Monte Carlo methods simulate photon transport, scattering, and detection, helping optimize system components.
Correct answer is: Accurate modeling of photon interactions and system response
Q.113 In a SPECT acquisition, the term "orbit radius" refers to:
The distance from the centre of rotation to the detector face
The radius of the collimator holes
The size of the patient’s head
The energy of the detected photons
Explanation - Orbit radius defines how far the detector is from the patient, influencing magnification and resolution.
Correct answer is: The distance from the centre of rotation to the detector face
Q.114 Which of the following SPECT tracers is most appropriate for assessing cerebral amyloid deposition in Alzheimer’s disease?
I‑123‑iodobenzamide
Tc‑99m‑HMPAO
I‑123‑florbetapir
F‑18‑florbetapir
Explanation - I‑123‑florbetapir binds to amyloid plaques, allowing SPECT visualization of amyloid burden.
Correct answer is: I‑123‑florbetapir
Q.115 In SPECT imaging, a “window‑based scatter correction” uses:
A second (lower) energy window to estimate scattered photons
A higher energy window to capture primary photons
The same window with longer acquisition time
Physical filters placed in front of the detector
Explanation - Scatter correction often employs a lower‑energy window to sample scattered photons, which are then subtracted from the primary window counts.
Correct answer is: A second (lower) energy window to estimate scattered photons
Q.116 The term "projection matrix" in SPECT reconstruction refers to:
A mathematical representation linking image voxels to measured projection data
The physical arrangement of collimator holes
The layout of the detector crystals
The energy spectrum of the radionuclide
Explanation - The projection matrix defines how each voxel contributes to each measured projection, essential for iterative reconstruction.
Correct answer is: A mathematical representation linking image voxels to measured projection data
Q.117 Which of the following is a typical step in the SPECT quality‑control (QC) routine performed daily?
Uniformity test using a flood source
Calibration of the CT scanner
Measurement of the radiopharmaceutical’s half‑life
Adjustment of patient positioning aids
Explanation - Daily uniformity checks ensure the detector response is even across the field of view.
Correct answer is: Uniformity test using a flood source
Q.118 In SPECT, why is it important to keep the patient’s head stationary during brain imaging?
Even slight motion can cause significant blurring due to high spatial resolution requirements
Motion reduces the radiopharmaceutical’s half‑life
The collimator needs a fixed reference point
The detector cooling system depends on patient stillness
Explanation - Brain SPECT requires high resolution; even small movements can degrade image quality substantially.
Correct answer is: Even slight motion can cause significant blurring due to high spatial resolution requirements
Q.119 Which of the following SPECT acquisition protocols is most suitable for assessing myocardial viability?
Rest‑stress perfusion using Tc‑99m‑sestamibi
Dynamic acquisition with I‑123‑MIBG
Single static acquisition with Ga‑67
Whole‑body survey with F‑18 FDG
Explanation - Rest‑stress protocols with Tc‑99m sestamibi evaluate perfusion deficits and viability of myocardial tissue.
Correct answer is: Rest‑stress perfusion using Tc‑99m‑sestamibi
Q.120 What is the main purpose of performing a “dead‑time correction” in SPECT data processing?
To compensate for count losses occurring at high count rates
To adjust for photon attenuation
To align the CT and SPECT datasets
To increase the spatial resolution of the image
Explanation - Dead‑time correction restores the true count rate by accounting for detector inactivity periods after each event.
Correct answer is: To compensate for count losses occurring at high count rates
Q.121 A SPECT system uses a 20% energy window centered at 140 keV. If the system records 1 × 10⁶ total counts in the primary window and 2 × 10⁵ counts in the scatter window (centered at 120 keV), the scatter‑corrected primary counts are:
800 000
1 200 000
1 000 000
1 400 000
Explanation - Scatter‑corrected counts = primary – scatter = 1 000 000 – 200 000 = 800 000.
Correct answer is: 800 000
Q.122 In a SPECT scan of the lung using 99mTc‑DTPA, the most common cause of a false‑negative result is:
Attenuation from overlying bone
Patient’s deep inspiration causing reduced tracer deposition
High collimator sensitivity
Use of a high‑resolution collimator
Explanation - The ribs can attenuate gamma photons, leading to under‑estimation of lung activity if not corrected.
Correct answer is: Attenuation from overlying bone
Q.123 Which of the following is a benefit of using a “list‑mode” acquisition for gated cardiac SPECT studies?
Allows retrospective selection of cardiac phases without re‑acquisition
Reduces the need for attenuation correction
Increases the detector’s energy resolution
Eliminates the need for a collimator
Explanation - List‑mode stores timestamps, enabling flexible gating based on ECG after data collection.
Correct answer is: Allows retrospective selection of cardiac phases without re‑acquisition
Q.124 The term "field‑of‑view" (FOV) in a SPECT camera primarily depends on:
Detector crystal size and collimator geometry
The half‑life of the radiotracer
The reconstruction algorithm used
The patient’s body mass index
Explanation - FOV is determined by the physical dimensions of the detector and the collimator design, dictating the area that can be imaged.
Correct answer is: Detector crystal size and collimator geometry
Q.125 Which of the following best describes the role of the "lead‑shielded collimator" in a SPECT system?
To block photons that are not traveling parallel to the hole axis, improving spatial resolution
To increase the energy of incoming photons
To cool the detector crystal
To generate secondary photons for enhanced imaging
Explanation - The lead‑shielded collimator’s holes act as angular filters, allowing only photons aligned with the hole’s axis to reach the detector.
Correct answer is: To block photons that are not traveling parallel to the hole axis, improving spatial resolution