Q.1 What isotopic tracer is most commonly used in PET imaging?
Fluorine-18
Carbon-14
Iodine-131
Technetium-99m
Explanation - Fluorine‑18 (especially as ^18F‑FDG) has a convenient half‑life (≈110 min) and forms positrons suitable for PET.
Correct answer is: Fluorine-18
Q.2 In PET, the positron emitted by the radionuclide travels a short distance before annihilating with an electron. What are the typical energies of the two resulting photons?
511 keV each
250 keV each
1 MeV each
100 keV each
Explanation - Annihilation of a positron with an electron produces two 511 keV photons emitted approximately 180° apart.
Correct answer is: 511 keV each
Q.3 Which of the following best describes the principle of coincidence detection in PET?
Detecting two photons simultaneously to locate the annihilation event
Measuring the decay rate of the radionuclide
Counting single photons over time
Using a magnetic field to focus positrons
Explanation - Coincidence detection records pairs of 511 keV photons that arrive at detectors within a narrow time window, defining a line of response (LOR).
Correct answer is: Detecting two photons simultaneously to locate the annihilation event
Q.4 What is the most common radiopharmaceutical used for oncological PET scans?
^[18F]FDG (fluorodeoxyglucose)
^[99mTc]MIBI
^[131I]NaI
^[67Ga]citrate
Explanation - ^18F‑FDG accumulates in metabolically active cells, making it ideal for detecting many cancers.
Correct answer is: ^[18F]FDG (fluorodeoxyglucose)
Q.5 Which detector material is most widely used in modern PET scanners?
Lutetium‑yttrium oxyorthosilicate (LYSO)
Sodium iodide (NaI)
Germanium (Ge)
Bismuth germanate (BGO)
Explanation - LYSO offers high light output, fast decay time, and good stopping power, improving timing resolution.
Correct answer is: Lutetium‑yttrium oxyorthosilicate (LYSO)
Q.6 The spatial resolution of a PET system is primarily limited by:
Positron range and detector size
Patient motion only
Radioactive half‑life
Magnetic field strength
Explanation - Positron travel before annihilation blurs the exact location, and finite detector elements limit precision.
Correct answer is: Positron range and detector size
Q.7 Which correction is applied to PET data to compensate for non‑uniform attenuation of photons in the body?
Attenuation correction using CT data
Scatter correction using MRI
Time‑of‑flight correction
Energy window correction
Explanation - Hybrid PET/CT scanners use the CT image to calculate attenuation maps for correcting PET counts.
Correct answer is: Attenuation correction using CT data
Q.8 Time‑of‑flight (TOF) PET improves image quality by:
Measuring the difference in arrival times of the two photons
Increasing the injected tracer dose
Using a higher energy window
Applying a magnetic field
Explanation - TOF PET estimates the annihilation point along the LOR, reducing noise and improving signal‑to‑noise ratio.
Correct answer is: Measuring the difference in arrival times of the two photons
Q.9 In quantitative PET, the standardized uptake value (SUV) is expressed in:
g·cm⁻³·min⁻¹·MBq⁻¹
dimensionless ratio
counts per second
percentage of injected dose
Explanation - SUV = (tissue activity concentration [kBq/mL]) / (injected dose [kBq] / body weight [g]), yielding a unitless value.
Correct answer is: dimensionless ratio
Q.10 Which physiological process does ^18F‑FDG PET primarily image?
Glucose metabolism
Oxygen consumption
Blood flow
Protein synthesis
Explanation - ^18F‑FDG is a glucose analog taken up by cells via glucose transporters and phosphorylated, reflecting metabolic activity.
Correct answer is: Glucose metabolism
Q.11 The half‑life of Fluorine‑18 is approximately:
110 minutes
24 hours
6 minutes
2 days
Explanation - The 110‑minute half‑life balances production logistics and patient radiation dose.
Correct answer is: 110 minutes
Q.12 Which of the following is NOT a typical indication for PET imaging?
Assessment of bone fracture healing
Staging of lymphoma
Evaluation of Alzheimer’s disease
Detection of myocardial viability
Explanation - Bone healing is usually evaluated with X‑ray, CT, or MRI; PET is not standard for this purpose.
Correct answer is: Assessment of bone fracture healing
Q.13 In a PET/CT system, why is the CT scan performed first?
To obtain attenuation maps before PET acquisition
Because CT requires the patient to be awake
To reduce radiation dose to the PET detectors
CT data are needed for motion correction only
Explanation - CT provides an electron density map used for attenuation correction of PET data.
Correct answer is: To obtain attenuation maps before PET acquisition
Q.14 Which of the following radionuclides emits only positrons (no gamma rays) and is therefore ideal for PET?
Carbon‑11
Iodine‑131
Technetium‑99m
Gallium‑67
Explanation - Carbon‑11 decays by β⁺ emission (positrons) with a 20‑minute half‑life, producing pure PET signals.
Correct answer is: Carbon‑11
Q.15 What is the main advantage of using a digital silicon photomultiplier (SiPM) over traditional photomultiplier tubes in PET detectors?
Higher timing resolution and compactness
Lower cost per detector
Ability to detect gamma rays directly
Elimination of the need for scintillators
Explanation - SiPMs provide fast response and can be tiled tightly, improving TOF performance.
Correct answer is: Higher timing resolution and compactness
Q.16 Which reconstruction algorithm is most commonly used in clinical PET to produce images from raw projection data?
Iterative Ordered Subset Expectation Maximization (OSEM)
Filtered Back Projection (FBP) only
Fourier Transform Reconstruction
Radon Transform Inversion
Explanation - OSEM accelerates the EM algorithm, yielding high‑quality images with manageable computation time.
Correct answer is: Iterative Ordered Subset Expectation Maximization (OSEM)
Q.17 In PET, scatter correction is necessary because:
Some photons undergo Compton scattering, altering their path and energy
Positrons may travel too far before annihilation
The detector temperature fluctuates
The patient’s heart beats during acquisition
Explanation - Scattered photons may be detected within the energy window, causing blurring if not corrected.
Correct answer is: Some photons undergo Compton scattering, altering their path and energy
Q.18 Which PET radiotracer is specifically designed to bind to amyloid plaques in the brain?
^[18F]Florbetapir
^[18F]FDG
^[13N]Ammonia
^[68Ga]DOTATATE
Explanation - ^18F‑Florbetapir (Amyvid) binds amyloid‑β plaques, aiding Alzheimer’s disease diagnosis.
Correct answer is: ^[18F]Florbetapir
Q.19 What is the typical injected activity of ^18F‑FDG for an adult PET scan?
370–740 MBq (10–20 mCi)
50–100 MBq (1–2.7 mCi)
1–2 GBq (27–54 mCi)
5–10 MBq (0.13–0.27 mCi)
Explanation - This dose provides sufficient counts while keeping radiation exposure within safe limits.
Correct answer is: 370–740 MBq (10–20 mCi)
Q.20 Which physiological parameter can be derived from dynamic PET imaging with compartmental modeling?
Rate constants for tracer uptake and washout
Blood pressure
Electrocardiogram (ECG) waveform
Bone mineral density
Explanation - Dynamic scans allow estimation of kinetic parameters like K1, k2, etc., reflecting tissue physiology.
Correct answer is: Rate constants for tracer uptake and washout
Q.21 A PET scanner with a 400 ps coincidence timing resolution can theoretically improve signal‑to‑noise ratio by:
≈2‑fold compared to non‑TOF PET
No improvement; timing does not affect SNR
≈10‑fold
Decrease SNR due to noise
Explanation - Better timing resolution localizes events more precisely, roughly doubling SNR in typical clinical scenarios.
Correct answer is: ≈2‑fold compared to non‑TOF PET
Q.22 Which organ typically shows the highest physiological uptake of ^18F‑FDG in a normal adult?
Brain
Liver
Spleen
Kidney
Explanation - The brain's high glucose metabolism leads to intense FDG uptake, useful for neurological assessments.
Correct answer is: Brain
Q.23 The term 'partial volume effect' in PET refers to:
Loss of apparent activity in small structures due to limited spatial resolution
Partial decay of the radionuclide during acquisition
Variation of detector sensitivity across the field of view
Changes in patient positioning
Explanation - When an object is smaller than about twice the system's resolution, measured activity is underestimated.
Correct answer is: Loss of apparent activity in small structures due to limited spatial resolution
Q.24 Which of the following statements about PET/MRI hybrid systems is TRUE?
MRI provides attenuation maps without ionizing radiation
MRI cannot be used with PET due to magnetic interference
PET/MRI systems have higher radiation dose than PET/CT
MRI replaces the need for any attenuation correction
Explanation - MRI‑based attenuation correction methods (e.g., Dixon sequences) enable PET/MRI without extra X‑ray exposure.
Correct answer is: MRI provides attenuation maps without ionizing radiation
Q.25 For cardiac viability studies, which PET tracer is most commonly used?
^[13N]Ammonia
^[18F]FDG
^[68Ga]DOTATATE
^[99mTc]Sestamibi
Explanation - FDG uptake indicates metabolically active myocardium, helping differentiate viable from scar tissue.
Correct answer is: ^[18F]FDG
Q.26 During a PET scan, why is the patient often asked to fast for several hours before ^18F‑FDG injection?
To lower serum glucose levels and improve tumor‑to‑background contrast
To reduce the radiation dose
Because FDG tastes bad
To avoid nausea during the scan
Explanation - High blood glucose competes with FDG for uptake, diminishing image quality.
Correct answer is: To lower serum glucose levels and improve tumor‑to‑background contrast
Q.27 Which of the following best describes the term 'radiotracer biodistribution'?
The pattern of tracer uptake throughout the body after injection
The half‑life of the radionuclide
The manufacturing process of the tracer
The cost of the radiopharmaceutical
Explanation - Biodistribution reflects how the tracer is absorbed, metabolized, and cleared by tissues.
Correct answer is: The pattern of tracer uptake throughout the body after injection
Q.28 What is the primary purpose of using a 'randoms correction' in PET data processing?
To remove coincidences that occur by chance, not from the same annihilation event
To correct for patient motion
To adjust for detector gain drift
To compensate for radioactive decay during acquisition
Explanation - Random coincidences add background noise; statistical methods estimate and subtract them.
Correct answer is: To remove coincidences that occur by chance, not from the same annihilation event
Q.29 A PET scanner with a 4 mm full‑width‑at‑half‑maximum (FWHM) spatial resolution will have a point spread function that:
Spreads the signal over about 4 mm in the image
Has zero width
Is only dependent on the radionuclide half‑life
Is unrelated to detector design
Explanation - FWHM defines the width of the system's point spread function, indicating spatial resolution.
Correct answer is: Spreads the signal over about 4 mm in the image
Q.30 Which of these is a major safety consideration when handling PET radiopharmaceuticals?
Shielding from positron annihilation radiation
Risk of magnetic field exposure
Risk of laser eye injury
Risk of high voltage electric shock
Explanation - Annihilation photons are 511 keV gamma rays; proper lead shielding protects staff.
Correct answer is: Shielding from positron annihilation radiation
Q.31 In PET imaging, the term 'dead time' refers to:
The period after a detection event during which the system cannot record another event
The time required for the radiotracer to reach steady state
The interval between patient positioning and scan start
The duration of the radiotracer synthesis
Explanation - Dead time causes count losses at high activity levels, affecting quantitative accuracy.
Correct answer is: The period after a detection event during which the system cannot record another event
Q.32 Which of the following is NOT a typical source of noise in PET images?
Electronic noise from the detector electronics
Statistical Poisson noise from limited counts
Thermal noise from the patient’s body
Random coincidences
Explanation - Patient thermal emissions do not generate gamma photons; other sources dominate image noise.
Correct answer is: Thermal noise from the patient’s body
Q.33 What is the main advantage of using ^68Ga‑labelled peptides over ^18F‑FDG for neuroendocrine tumor imaging?
Higher specificity for somatostatin receptors
Longer half‑life allowing delayed imaging
Lower cost of production
Ability to image bone directly
Explanation - ^68Ga‑DOTATATE binds somatostatin receptors overexpressed in many neuroendocrine tumors, providing better lesion detection.
Correct answer is: Higher specificity for somatostatin receptors
Q.34 During PET acquisition, why is a ‘list‑mode’ data format sometimes preferred over ‘sinogram’ format?
It records each coincidence event individually, enabling flexible re‑binning and dynamic studies
It reduces the amount of data storage needed
It automatically corrects for attenuation
It eliminates the need for reconstruction
Explanation - List‑mode preserves time stamps for each event, useful for retrospective framing and motion correction.
Correct answer is: It records each coincidence event individually, enabling flexible re‑binning and dynamic studies
Q.35 Which of the following is a common artifact seen in PET images when the patient has metallic dental work?
Cold spot (photopenic region) due to photon attenuation
Hot spot (increased uptake) caused by metal activation
Blurred edges throughout the brain
Uniform over‑estimation of activity
Explanation - High‑density metal attenuates 511 keV photons, causing localized under‑estimation if not corrected.
Correct answer is: Cold spot (photopenic region) due to photon attenuation
Q.36 The term 'SUVmax' refers to:
The highest voxel value of SUV within a region of interest
The average SUV across the whole body
The minimum detectable SUV
The standardized uptake volume
Explanation - SUVmax is commonly used for lesion characterization because it is less affected by ROI placement.
Correct answer is: The highest voxel value of SUV within a region of interest
Q.37 Which PET tracer is used primarily for imaging myocardial perfusion?
^[13N]Ammonia
^[18F]FDG
^[68Ga]DOTATATE
^[11C]Methionine
Explanation - ^13N‑Ammonia is taken up proportionally to blood flow, enabling perfusion assessment.
Correct answer is: ^[13N]Ammonia
Q.38 In a PET study, a high tumor‑to‑background ratio (TBR) is desirable because:
It improves lesion detectability and diagnostic confidence
It reduces radiation exposure
It shortens the acquisition time
It eliminates the need for attenuation correction
Explanation - A higher TBR means the tumor stands out more clearly against surrounding tissue.
Correct answer is: It improves lesion detectability and diagnostic confidence
Q.39 Which of the following factors does NOT significantly affect the SUV measurement?
Patient’s height
Injected dose calibration error
Blood glucose level at the time of injection
Scanner’s timing resolution
Explanation - SUV is normalized to body weight (or lean body mass), not height; height alone does not directly affect it.
Correct answer is: Patient’s height
Q.40 The process of 'decay correction' in PET data is performed to:
Compensate for the loss of activity due to radioactive decay during the scan
Adjust for patient motion
Normalize the image to a reference organ
Eliminate scatter photons
Explanation - Decay correction scales counts so that activity is comparable across different acquisition times.
Correct answer is: Compensate for the loss of activity due to radioactive decay during the scan
Q.41 Which PET radiotracer is most suitable for imaging hypoxic regions within tumors?
^[18F]FMISO (Fluoromisonidazole)
^[18F]FDG
^[13N]Ammonia
^[68Ga]DOTATATE
Explanation - ^18F‑FMISO accumulates in low‑oxygen cells, allowing hypoxia mapping.
Correct answer is: ^[18F]FMISO (Fluoromisonidazole)
Q.42 In PET imaging, the term 'axial field of view' (AFOV) refers to:
The length of the scanner that can detect coincidences along the patient’s body
The width of each detector crystal
The angle between the two annihilation photons
The time window for coincidence detection
Explanation - A larger AFOV increases sensitivity and allows whole‑body imaging in a single bed position.
Correct answer is: The length of the scanner that can detect coincidences along the patient’s body
Q.43 Which of the following is a benefit of using a longer axial FOV PET scanner (e.g., 70 cm) compared with a conventional 20 cm scanner?
Higher sensitivity leading to lower injected dose or shorter scan time
Improved spatial resolution beyond physical limits
Elimination of the need for attenuation correction
Ability to image only the brain without moving the patient
Explanation - More detector coverage captures more coincidences, boosting count statistics.
Correct answer is: Higher sensitivity leading to lower injected dose or shorter scan time
Q.44 What is the primary cause of 'dead‑time loss' in a PET detector system?
Finite recovery time of the detector after each event
Photon attenuation in the patient
Scatter of photons in the detector crystal
Patient movement
Explanation - During dead time, subsequent events are missed, reducing measured counts.
Correct answer is: Finite recovery time of the detector after each event
Q.45 Which PET tracer is most commonly used for imaging neuroinflammation via the translocator protein (TSPO)?
^[11C]PK11195
^[18F]FDG
^[13N]Ammonia
^[68Ga]DOTATATE
Explanation - ^11C‑PK11195 binds TSPO, which is up‑regulated in activated microglia.
Correct answer is: ^[11C]PK11195
Q.46 In PET image reconstruction, the term 'regularization' is used to:
Suppress noise while preserving edges by adding a penalty term
Increase the number of detected coincidences
Accelerate the decay of the radionuclide
Correct for patient motion
Explanation - Regularization (e.g., TV, quadratic) stabilizes iterative algorithms against over‑fitting noise.
Correct answer is: Suppress noise while preserving edges by adding a penalty term
Q.47 Which factor most directly influences the quantitative accuracy of PET SUVs in multi‑center clinical trials?
Standardization of scanner calibration and reconstruction protocols
The brand of the CT scanner used for attenuation correction
The patient’s hair color
The time of day the scan is performed
Explanation - Consistent calibration and reconstruction reduce inter‑site variability in quantitative measures.
Correct answer is: Standardization of scanner calibration and reconstruction protocols
Q.48 What is the purpose of a 'warm‑up' scan before clinical PET acquisition?
To stabilize detector gain and electronics before patient imaging
To assess patient metabolism
To calibrate the CT component
To test the radiotracer purity
Explanation - Warm‑up runs allow the system to reach a steady operating state, reducing drift during the scan.
Correct answer is: To stabilize detector gain and electronics before patient imaging
Q.49 Which PET tracer is most suitable for imaging the prostate‑specific membrane antigen (PSMA) in prostate cancer?
^[68Ga]PSMA‑11
^[18F]FDG
^[13N]Ammonia
^[11C]Methionine
Explanation - ^68Ga‑PSMA‑11 binds the PSMA protein, providing high‑contrast images of prostate cancer lesions.
Correct answer is: ^[68Ga]PSMA‑11
Q.50 During a PET scan, the term 'bed position' refers to:
A discrete location of the patient table used to cover the full axial extent of the body
The angle at which detectors are tilted
The time interval between two successive scans
The specific energy window setting
Explanation - Multiple bed positions are acquired sequentially for whole‑body imaging.
Correct answer is: A discrete location of the patient table used to cover the full axial extent of the body
Q.51 Which of the following best describes the 'spill‑over' effect in PET imaging of the brain?
Activity from high‑uptake regions contaminates adjacent low‑uptake areas due to limited resolution
Tracer leaking from the injection site into the brain
Patient movement causing blurring
Incorrect attenuation correction leading to overestimation
Explanation - Limited spatial resolution causes counts to bleed into neighboring voxels, especially at tissue borders.
Correct answer is: Activity from high‑uptake regions contaminates adjacent low‑uptake areas due to limited resolution
Q.52 Which PET tracer is used to evaluate amyloid deposition in the brain for Alzheimer's disease?
^[18F]Florbetapir
^[18F]FDG
^[68Ga]DOTATATE
^[13N]Ammonia
Explanation - ^18F‑Florbetapir binds amyloid plaques, aiding in early AD diagnosis.
Correct answer is: ^[18F]Florbetapir
Q.53 In PET, the 'energy window' is set around 511 keV to:
Accept true annihilation photons while rejecting scattered ones
Control the timing resolution
Determine the injected dose
Adjust the magnetic field strength
Explanation - A narrow energy window (e.g., 425–650 keV) reduces inclusion of lower‑energy scattered photons.
Correct answer is: Accept true annihilation photons while rejecting scattered ones
Q.54 Which of the following is an advantage of using ^15O‑water as a PET tracer?
It provides a quantitative measure of regional blood flow
It has a half‑life of several days, allowing delayed imaging
It binds specifically to tumor receptors
It does not produce positrons
Explanation - ^15O‑water is a freely diffusible tracer whose uptake is directly proportional to perfusion.
Correct answer is: It provides a quantitative measure of regional blood flow
Q.55 The term 'dead‑time correction factor' is applied to PET data to:
Compensate for lost counts due to detector recovery time
Normalize the SUV to body surface area
Correct for photon attenuation
Remove motion artifacts
Explanation - Correction restores true count rates, especially important at high activity levels.
Correct answer is: Compensate for lost counts due to detector recovery time
Q.56 Which of the following is a primary clinical use of ^68Ga‑DOTATATE PET?
Imaging neuroendocrine tumors via somatostatin receptor binding
Assessing myocardial perfusion
Evaluating bone metabolism
Measuring cerebral glucose metabolism
Explanation - ^68Ga‑DOTATATE binds somatostatin receptors overexpressed in many NETs.
Correct answer is: Imaging neuroendocrine tumors via somatostatin receptor binding
Q.57 When a PET scanner uses a 'dual‑head' configuration, what does this mean?
Two detector rings opposite each other capture coincidences
The scanner can perform both PET and SPECT simultaneously
It has both PET and MRI components
It can acquire two energy windows at once
Explanation - Dual‑head designs have two opposing detector panels; modern scanners often have many rings.
Correct answer is: Two detector rings opposite each other capture coincidences
Q.58 What does the term 'photon non‑collinearity' refer to in PET imaging?
The slight deviation from exactly 180° between the two annihilation photons
Photons traveling at different speeds
The emission of a third photon during decay
The variation in photon energy
Explanation - Due to residual momentum of the electron‑positron pair, photons are not perfectly collinear, limiting resolution.
Correct answer is: The slight deviation from exactly 180° between the two annihilation photons
Q.59 In a PET scan of a patient with high blood glucose (>200 mg/dL), what is the most likely impact on ^18F‑FDG image quality?
Reduced tumor uptake and lower contrast
Increased background noise
Higher radiation dose to the patient
No impact; glucose level does not affect FDG uptake
Explanation - Elevated glucose competes with FDG for transport and phosphorylation, decreasing lesion visibility.
Correct answer is: Reduced tumor uptake and lower contrast
Q.60 Which correction method is essential for accurate quantification in PET when the patient breathes shallowly during acquisition?
Respiratory gating
Attenuation correction
Randoms correction
Dead‑time correction
Explanation - Gating synchronizes data acquisition with the respiratory cycle, reducing motion blur.
Correct answer is: Respiratory gating
Q.61 What is the main purpose of using a 'phantom' in PET quality assurance?
To evaluate system performance parameters such as uniformity, resolution, and sensitivity
To calibrate the CT scanner
To train technologists in patient positioning
To produce radiotracers
Explanation - Phantoms contain known activity distributions, allowing objective testing of PET performance.
Correct answer is: To evaluate system performance parameters such as uniformity, resolution, and sensitivity
Q.62 Which PET radiotracer is most appropriate for imaging dopamine transporter density in Parkinson’s disease?
^[18F]FP‑CIT
^[18F]FDG
^[13N]Ammonia
^[68Ga]DOTATATE
Explanation - ^18F‑FP‑CIT binds to the dopamine transporter, revealing nigrostriatal degeneration.
Correct answer is: ^[18F]FP‑CIT
Q.63 In PET, why is a 'coincidence time window' typically set to a few nanoseconds?
To ensure that only true coincident photon pairs from the same annihilation are counted
To reduce the effect of patient motion
To allow for longer-lived isotopes
To increase the detector’s energy resolution
Explanation - A narrow time window discriminates true coincidences from random ones.
Correct answer is: To ensure that only true coincident photon pairs from the same annihilation are counted
Q.64 Which PET tracer is widely used for imaging hypoxic tumor regions and is labeled with ^18F?
^[18F]FMISO
^[18F]FDG
^[13N]Ammonia
^[68Ga]DOTATATE
Explanation - ^18F‑FMISO is retained in hypoxic cells, providing a marker for tumor oxygenation.
Correct answer is: ^[18F]FMISO
Q.65 What is the effect of increasing the 'iteration number' in OSEM reconstruction on PET image quality?
Improves contrast but may increase image noise
Reduces spatial resolution
Eliminates the need for attenuation correction
Shortens acquisition time
Explanation - More iterations converge toward the true solution, enhancing detail but amplifying statistical noise.
Correct answer is: Improves contrast but may increase image noise
Q.66 Which of the following is the primary reason for using a 'low‑dose CT' in PET/CT for attenuation correction?
To minimize additional radiation exposure while providing sufficient data for correction
Because high‑dose CT would interfere with PET detectors
Low‑dose CT provides better soft‑tissue contrast
Low‑dose CT is required for TOF PET
Explanation - A low‑dose CT is sufficient for attenuation maps, keeping the total dose low.
Correct answer is: To minimize additional radiation exposure while providing sufficient data for correction
Q.67 Which PET tracer is used to evaluate myocardial fatty acid metabolism?
^[18F]FTHA (Fluoro‑triolein)
^[18F]FDG
^[13N]Ammonia
^[68Ga]DOTATATE
Explanation - ^18F‑FTHA is a fatty acid analog that is taken up by cardiac myocytes, reflecting fatty acid utilization.
Correct answer is: ^[18F]FTHA (Fluoro‑triolein)
Q.68 In PET, the term 'sensitivity' is defined as:
The fraction of true coincidences detected per unit activity
The spatial resolution of the scanner
The amount of radiation dose to the patient
The time required for image reconstruction
Explanation - Higher sensitivity yields more counts for a given administered activity.
Correct answer is: The fraction of true coincidences detected per unit activity
Q.69 Which PET tracer is most appropriate for imaging inflammation via the translocator protein (TSPO) in the brain?
^[11C]PK11195
^[18F]FDG
^[68Ga]DOTATATE
^[13N]Ammonia
Explanation - ^11C‑PK11195 binds TSPO, which is up‑regulated in activated microglia.
Correct answer is: ^[11C]PK11195
Q.70 Which of the following best explains why PET can provide absolute quantitative measurements (e.g., activity concentration in kBq/mL) whereas SPECT generally provides relative values?
PET detects coincident photon pairs, allowing direct calibration to activity, while SPECT relies on single photon detection with variable efficiency
PET uses higher energy photons than SPECT
SPECT detectors are less sensitive than PET detectors
PET scans are always longer than SPECT scans
Explanation - Coincidence detection yields a linear relationship between count rate and activity, facilitating absolute quantification.
Correct answer is: PET detects coincident photon pairs, allowing direct calibration to activity, while SPECT relies on single photon detection with variable efficiency
Q.71 During a PET acquisition, a 'single photon emission' event is recorded. What is the most likely cause?
Scatter or random coincidence where only one of the annihilation photons is detected
The tracer decayed without emitting a positron
A detector malfunction
The patient moved out of the field of view
Explanation - Single events are usually discarded; they arise from scattered photons or random coincidences.
Correct answer is: Scatter or random coincidence where only one of the annihilation photons is detected
Q.72 Which PET tracer is specifically designed for imaging the prostate cancer-specific antigen PSMA?
^[68Ga]PSMA‑11
^[18F]FDG
^[13N]Ammonia
^[11C]Methionine
Explanation - ^68Ga‑PSMA‑11 binds PSMA, enabling highly specific prostate cancer imaging.
Correct answer is: ^[68Ga]PSMA‑11
Q.73 In a PET scan, the 'line of response' (LOR) represents:
The straight line connecting the two detectors that recorded a coincident event
The trajectory of the radiotracer in the bloodstream
The path of the patient movement during acquisition
The energy spectrum of detected photons
Explanation - Each coincidence defines an LOR, which is used in image reconstruction to localize the source.
Correct answer is: The straight line connecting the two detectors that recorded a coincident event
Q.74 Which of the following is a major limitation of ^15O‑water PET for routine clinical use?
Very short half‑life (≈2 min) requiring an on‑site cyclotron
High radiation dose to the patient
Low spatial resolution
Inability to quantify blood flow
Explanation - The short half‑life mandates immediate synthesis and delivery, limiting widespread clinical availability.
Correct answer is: Very short half‑life (≈2 min) requiring an on‑site cyclotron
Q.75 What is the principal advantage of using a 'digital photon counter' in PET over an analog photomultiplier?
Improved timing resolution and reduced electronic noise
Lower cost per detector
Ability to operate at higher temperatures
No need for scintillator crystals
Explanation - Digital photon counters (e.g., SiPMs) provide fast, low‑noise signal processing, enhancing TOF performance.
Correct answer is: Improved timing resolution and reduced electronic noise
Q.76 Which PET radiotracer is most commonly used for imaging the serotonin transporter (SERT) in the brain?
^[11C]DASB
^[18F]FDG
^[13N]Ammonia
^[68Ga]DOTATATE
Explanation - ^11C‑DASB binds selectively to SERT, enabling assessment of serotonergic function.
Correct answer is: ^[11C]DASB
Q.77 Which factor primarily determines the maximum permissible injected activity of a PET tracer for a given patient?
Regulatory dose limits based on radiation safety
The cost of the radiopharmacy
The patient’s height
The scanner’s axial field of view
Explanation - Guidelines (e.g., ICRP) define maximum activities to keep dose within safe limits.
Correct answer is: Regulatory dose limits based on radiation safety
Q.78 Which of the following best describes the term 'quantitative PET'?
Measurement of absolute tracer concentration (e.g., kBq/mL) in tissues
Acquisition of images with higher visual contrast only
Use of PET only for anatomical localization
Scanning without any correction algorithms
Explanation - Quantitative PET provides numeric values of activity, enabling kinetic modeling and therapy monitoring.
Correct answer is: Measurement of absolute tracer concentration (e.g., kBq/mL) in tissues
Q.79 When performing a PET scan for a pediatric patient, which strategy is commonly used to reduce radiation exposure?
Lowering the injected activity based on body weight
Increasing the scan duration
Using a higher energy window
Skipping attenuation correction
Explanation - Weight‑based dosing reduces dose while maintaining adequate image quality.
Correct answer is: Lowering the injected activity based on body weight
Q.80 What is the main purpose of a 'scatter correction' algorithm in PET image reconstruction?
To subtract counts originating from photons that have undergone Compton scattering
To adjust for patient movement
To compensate for detector dead time
To increase the injected activity
Explanation - Scatter adds a low‑resolution background; correction improves contrast and quantitative accuracy.
Correct answer is: To subtract counts originating from photons that have undergone Compton scattering
Q.81 Which PET tracer is specifically utilized for imaging the amyloid plaque burden in Alzheimer's disease?
^[18F]Florbetapir
^[18F]FDG
^[13N]Ammonia
^[68Ga]DOTATATE
Explanation - ^18F‑Florbetapir binds amyloid‑β plaques, providing a diagnostic tool for AD.
Correct answer is: ^[18F]Florbetapir
Q.82 In the context of PET detector design, what does the term 'photodetector gain' refer to?
The amplification factor of the electrical signal generated by photon interaction
The increase in spatial resolution
The ability to detect high‑energy photons
The speed of data transmission
Explanation - Gain determines how much the initial light pulse is amplified into a measurable electrical pulse.
Correct answer is: The amplification factor of the electrical signal generated by photon interaction
Q.83 Which of the following statements about 'partial volume correction' (PVC) in PET is TRUE?
PVC attempts to recover true activity in small structures by accounting for limited spatial resolution
PVC eliminates the need for attenuation correction
PVC reduces the injected dose needed for imaging
PVC is only applicable to brain PET studies
Explanation - PVC uses mathematical models to compensate for activity spill‑out/in, improving quantitative accuracy.
Correct answer is: PVC attempts to recover true activity in small structures by accounting for limited spatial resolution
Q.84 When a PET scanner reports a 'sensitivity' of 7 cps/kBq, what does this mean?
The scanner records 7 true coincidence counts per second for each kilobecquerel of activity present
The scanner can detect photons of 7 keV energy
The patient receives 7 mSv of radiation per scan
The detector crystals are 7 mm thick
Explanation - Sensitivity expresses the count rate per unit activity, reflecting system efficiency.
Correct answer is: The scanner records 7 true coincidence counts per second for each kilobecquerel of activity present
Q.85 Which of the following PET tracers is most appropriate for assessing tumor proliferation?
^[18F]FLT (Fluorothymidine)
^[18F]FDG
^[13N]Ammonia
^[68Ga]DOTATATE
Explanation - ^18F‑FLT is taken up by proliferating cells via thymidine kinase activity, serving as a proliferation marker.
Correct answer is: ^[18F]FLT (Fluorothymidine)
Q.86 Which of the following is a primary source of systematic error in PET quantification if not corrected?
Attenuation of 511 keV photons within the body
Variations in the patient’s heart rate
Ambient temperature in the scanner room
Noise from the MRI gradient coils
Explanation - Attenuation reduces detected counts; without correction, SUVs are underestimated, especially in deep tissues.
Correct answer is: Attenuation of 511 keV photons within the body
Q.87 What does the term 'dynamic PET' refer to?
Acquisition of a series of time‑resolved frames to study tracer kinetics
Scanning the patient while they are exercising
Using a rotating detector ring
Applying a high‑energy window during acquisition
Explanation - Dynamic scans capture the temporal distribution of tracer, enabling kinetic modeling.
Correct answer is: Acquisition of a series of time‑resolved frames to study tracer kinetics
Q.88 Which of the following is NOT a typical use of PET in oncology?
Assessing bone density
Staging of lymphomas
Evaluating treatment response
Detecting metastatic disease
Explanation - Bone density is measured with DXA or CT; PET evaluates metabolic activity, not mineral content.
Correct answer is: Assessing bone density
Q.89 Which PET tracer is most commonly used for imaging neuroendocrine tumors that overexpress somatostatin receptors?
^[68Ga]DOTATATE
^[18F]FDG
^[13N]Ammonia
^[11C]Methionine
Explanation - ^68Ga‑DOTATATE binds somatostatin receptors, providing high sensitivity for NETs.
Correct answer is: ^[68Ga]DOTATATE
Q.90 In PET imaging, the 'time‑of‑flight' (TOF) technique primarily improves:
Signal‑to‑noise ratio by localizing events along the LOR
Spatial resolution beyond the detector size
The half‑life of the radionuclide
The energy resolution of the detectors
Explanation - TOF measures the arrival time difference of the two photons, narrowing the possible annihilation point.
Correct answer is: Signal‑to‑noise ratio by localizing events along the LOR
Q.91 Which PET tracer is used for imaging the dopamine transporter in Parkinson’s disease?
^[18F]FP‑CIT
^[18F]FDG
^[68Ga]DOTATATE
^[13N]Ammonia
Explanation - ^18F‑FP‑CIT binds the dopamine transporter, allowing visualization of nigrostriatal degeneration.
Correct answer is: ^[18F]FP‑CIT
Q.92 When performing PET attenuation correction with CT data, which of the following is required?
Conversion of CT Hounsfield units to linear attenuation coefficients at 511 keV
Direct use of CT images without any conversion
Acquisition of a separate low‑dose SPECT scan
Application of a magnetic field map
Explanation - CT values must be scaled to photon energies of 511 keV for accurate PET attenuation correction.
Correct answer is: Conversion of CT Hounsfield units to linear attenuation coefficients at 511 keV
Q.93 Which of the following best describes the 'partial volume effect' in PET imaging?
Underestimation of activity in structures smaller than about twice the system's spatial resolution
Overestimation of activity due to high injected dose
Random coincidences causing background noise
Photon non‑collinearity increasing image blur
Explanation - Limited resolution causes spill‑out of counts from small objects, reducing measured activity.
Correct answer is: Underestimation of activity in structures smaller than about twice the system's spatial resolution
Q.94 Which PET tracer is most suitable for imaging myocardial fatty‑acid metabolism?
^[18F]FTHA
^[18F]FDG
^[13N]Ammonia
^[68Ga]DOTATATE
Explanation - ^18F‑FTHA mimics fatty acids and is taken up by the myocardium, reflecting fatty‑acid utilization.
Correct answer is: ^[18F]FTHA
Q.95 What is the primary reason for performing a low‑dose CT scan before the PET acquisition in PET/CT?
To generate an attenuation map for correcting PET data
To replace the need for a PET scan
To increase the PET detector sensitivity
To calibrate the PET timing electronics
Explanation - The CT provides electron density information required for attenuation correction of PET photons.
Correct answer is: To generate an attenuation map for correcting PET data
Q.96 In PET imaging, the term 'dead‑time loss' becomes significant when:
The activity concentration is high, causing many events to arrive within the detector’s recovery time
The patient moves slowly
The scan is performed at low temperature
The injected dose is too low
Explanation - High count rates saturate detector electronics, leading to missed coincidences.
Correct answer is: The activity concentration is high, causing many events to arrive within the detector’s recovery time
Q.97 Which of the following PET radiotracers is most appropriate for imaging inflammation via the translocator protein (TSPO) in the brain?
^[11C]PK11195
^[18F]FDG
^[68Ga]DOTATATE
^[13N]Ammonia
Explanation - ^11C‑PK11195 binds TSPO, which is up‑regulated in activated microglia during neuroinflammation.
Correct answer is: ^[11C]PK11195
Q.98 The most common cause of 'random coincidences' in PET is:
Two unrelated photons arriving within the coincidence time window
Scatter photons that have lost energy
Positron range before annihilation
Patient motion during acquisition
Explanation - Random coincidences arise from chance detection of two unrelated photons that happen to fall within the timing window.
Correct answer is: Two unrelated photons arriving within the coincidence time window
Q.99 Which PET tracer is used to assess hypoxia in solid tumors?
^[18F]FMISO
^[18F]FDG
^[13N]Ammonia
^[68Ga]DOTATATE
Explanation - ^18F‑FMISO accumulates in low‑oxygen cells, providing a non‑invasive hypoxia map.
Correct answer is: ^[18F]FMISO
Q.100 Which PET detector technology offers the fastest decay time, facilitating better TOF performance?
LYSO crystals coupled with SiPMs
NaI crystals with PMTs
BGO crystals with PMTs
CsI crystals with APDs
Explanation - LYSO has a decay time of ~40 ns, and SiPMs have fast response, together improving TOF timing.
Correct answer is: LYSO crystals coupled with SiPMs
Q.101 In PET imaging, why is the 'energy window' typically set between 425–650 keV?
To accept most true 511 keV photons while rejecting scattered photons of lower energy
To match the energy of the radiotracer decay
Because detectors cannot detect photons outside this range
To reduce the effect of random coincidences
Explanation - A window around 511 keV includes true events but excludes many scattered photons that have lost energy.
Correct answer is: To accept most true 511 keV photons while rejecting scattered photons of lower energy
Q.102 Which PET tracer is most suitable for imaging the dopamine D2 receptors in the brain?
^[11C]Raclopride
^[18F]FDG
^[68Ga]DOTATATE
^[13N]Ammonia
Explanation - ^11C‑Raclopride binds to D2 receptors, enabling assessment of dopaminergic function.
Correct answer is: ^[11C]Raclopride
Q.103 What does the term 'SUVmean' represent in PET quantification?
The average standardized uptake value within a region of interest
The maximum SUV in the image
The minimum detectable SUV
The SUV corrected for patient weight
Explanation - SUVmean provides a mean activity concentration normalized to injected dose and body weight.
Correct answer is: The average standardized uptake value within a region of interest
Q.104 Which of the following is a major challenge when performing PET/MRI compared to PET/CT?
Generating accurate attenuation maps without CT data
Higher radiation dose to the patient
Inability to perform TOF imaging
Longer acquisition times for the MRI component
Explanation - MRI does not directly provide electron density; specialized sequences and algorithms are required for attenuation correction.
Correct answer is: Generating accurate attenuation maps without CT data
Q.105 Which of the following radiotracers is most appropriate for imaging prostate‑specific membrane antigen (PSMA) in prostate cancer?
^[68Ga]PSMA‑11
^[18F]FDG
^[13N]Ammonia
^[11C]Methionine
Explanation - ^68Ga‑PSMA‑11 binds PSMA, providing high‑contrast images of prostate cancer lesions.
Correct answer is: ^[68Ga]PSMA‑11
Q.106 In PET imaging, the term 'axial coverage' refers to:
The length of the patient body that can be imaged in a single bed position
The width of each detector element
The time window for coincidence detection
The energy range of accepted photons
Explanation - Axial coverage determines how many bed positions are needed for whole‑body imaging.
Correct answer is: The length of the patient body that can be imaged in a single bed position
Q.107 Which of the following is a common quantitative metric derived from dynamic PET studies of the brain?
Binding potential (BP)
Standardized uptake value (SUV)
Hounsfield unit (HU)
Echo time (TE)
Explanation - BP quantifies receptor availability from kinetic modeling of dynamic PET data.
Correct answer is: Binding potential (BP)
Q.108 What is the main reason that PET scanners are often placed in shielded rooms with lead walls?
To protect staff and the public from 511 keV gamma radiation
To keep the temperature stable for the detectors
Because PET scanners generate magnetic fields
To reduce acoustic noise
Explanation - The annihilation photons are highly penetrating; lead shielding reduces radiation exposure outside the scanner.
Correct answer is: To protect staff and the public from 511 keV gamma radiation
Q.109 Which PET tracer is commonly used for imaging the serotonin transporter (SERT) in psychiatric research?
^[11C]DASB
^[18F]FDG
^[13N]Ammonia
^[68Ga]DOTATATE
Explanation - ^11C‑DASB binds specifically to SERT, enabling assessment of serotonergic pathways.
Correct answer is: ^[11C]DASB
Q.110 In a PET/CT system, what is the purpose of the 'CT dose modulation' feature?
To adjust the X‑ray tube current based on patient size, reducing radiation dose while maintaining image quality
To synchronize CT acquisition with PET timing
To increase the PET detector sensitivity
To change the PET acquisition time automatically
Explanation - Dose modulation tailors CT exposure, lowering dose especially in low‑attenuation regions.
Correct answer is: To adjust the X‑ray tube current based on patient size, reducing radiation dose while maintaining image quality
Q.111 Which factor most directly influences the achievable spatial resolution of a PET scanner?
Size of the scintillation crystal elements
Patient’s blood glucose level
Injected activity
Reconstruction algorithm only
Explanation - Smaller crystals provide finer sampling of photon interaction positions, improving resolution.
Correct answer is: Size of the scintillation crystal elements
Q.112 Which of the following is a primary clinical use of ^68Ga‑DOTATATE PET?
Imaging neuroendocrine tumors via somatostatin receptor targeting
Assessing myocardial perfusion
Measuring cerebral glucose metabolism
Evaluating bone metabolism
Explanation - ^68Ga‑DOTATATE binds somatostatin receptors, making it ideal for NET detection.
Correct answer is: Imaging neuroendocrine tumors via somatostatin receptor targeting
Q.113 What does the term 'list‑mode' acquisition mean in PET?
Each detected coincidence is recorded with its exact time stamp, allowing flexible post‑processing
Only a list of detected energies is stored
Data are stored as pre‑binned sinograms
The scanner records only the number of coincidences per minute
Explanation - List‑mode preserves full event information, enabling retrospective gating, re‑binning, and dynamic analysis.
Correct answer is: Each detected coincidence is recorded with its exact time stamp, allowing flexible post‑processing
Q.114 Which PET tracer is specifically used for imaging amyloid plaques in the brain?
^[18F]Florbetapir
^[18F]FDG
^[13N]Ammonia
^[68Ga]DOTATATE
Explanation - ^18F‑Florbetapir binds amyloid‑β plaques, aiding in the diagnosis of Alzheimer’s disease.
Correct answer is: ^[18F]Florbetapir
Q.115 What is the main purpose of applying a 'Gaussian filter' during PET image reconstruction?
To smooth the image and reduce high‑frequency noise
To increase the count rate
To correct for attenuation
To convert counts to SUV
Explanation - A Gaussian filter averages neighboring voxels, suppressing noise at the cost of some resolution.
Correct answer is: To smooth the image and reduce high‑frequency noise