NUCLEAR MEDICINE BOARD REVIEW WITH
Q&A|| LATEST UPDATE 2026
Section 1: Physics & Instrumentation (40 Questions)
Q1: What is the primary purpose of a photomultiplier tube (PMT) in a
gamma camera?
A: To convert the weak light scintillations from the crystal into a measurable
electrical signal and amplify it.
Q2: Define "energy resolution" in the context of a gamma camera.
A: It is the ability of the detector to distinguish between two photopeaks of
different energies. It is typically expressed as the Full Width at Half Maximum
(FWHM) of a photopeak.
Q3: What is the function of a collimator?
A: To define the field of view and spatially localize the source of gamma
emissions by only allowing photons traveling in a specific direction to reach the
detector crystal.
Q4: Which collimator type provides the highest sensitivity but the lowest
resolution?
A: A high-sensitivity (or low-resolution) collimator. It has wider holes and
thinner septa.
Q5: A technologist uses a 140 keV photopeak for a Technetium-99m scan.
What is the acceptable energy window?
A: A 20% window, which is calculated as 140 keV ± 10% (126 keV to 154
keV).
Q6: What is the purpose of the pulse height analyzer (PHA)?
A: To select only those electrical pulses that fall within the preselected energy
window, thereby rejecting scattered photons.
Q7: What is "dead time" in a gamma camera?
A: The time during which the system is processing a pulse and is unable to
process another event. This leads to count loss at high activities.
,Q8: Explain the difference between a paralyzable and a non-paralyzable
dead time model.
A: In a paralyzable model, every event (even those not counted) extends the
dead time. In a non-paralyzable model, the dead time is fixed for each recorded
event.
Q9: What is the purpose of a uniformity flood test?
A: To check the intrinsic or extrinsic uniformity of the gamma camera's
response to a uniform source of radioactivity. It helps detect crystal defects,
PMT issues, or collimator damage.
Q10: What is the difference between intrinsic and extrinsic uniformity
testing?
A: Intrinsic uniformity is tested without a collimator, assessing the crystal and
PMT system. Extrinsic uniformity is tested with a collimator in place, assessing
the entire imaging system.
Q11: What does a "bar phantom" test?
A: It tests the spatial resolution of the gamma camera system.
Q12: In SPECT imaging, what is the purpose of a "center of rotation"
(COR) calibration?
A: To correct for any misalignment between the mechanical axis of rotation and
the electronic center of the gamma camera's field of view.
Q13: What are the main advantages of PET imaging over SPECT imaging?
A: Higher sensitivity, better spatial resolution, and the ability to perform
accurate attenuation correction and absolute quantification of activity.
Q14: What is the physical principle behind Positron Emission Tomography
(PET)?
A: Annihilation of a positron with an electron, producing two 511 keV photons
emitted at approximately 180 degrees to each other.
Q15: What is a PET detector typically made of?
A: A scintillation crystal (e.g., LSO, BGO, or LYSO) coupled to a
photodetector (e.g., PMT or SiPM).
Q16: What is "time-of-flight" (TOF) PET?
A: A PET technique that measures the small difference in arrival time of the
two annihilation photons to more precisely localize the annihilation event along
the line of response, improving image quality.
Q17: What is the purpose of a "septa" in a PET scanner?
A: In 2D PET, septa are used to reduce the detection of scattered and random
, coincidences from outside the imaging plane. Modern 3D PET scanners do not
have septa.
Q18: Define "sensitivity" of a gamma camera.
A: The efficiency with which the camera detects gamma rays. It is typically
measured in counts per minute per microcurie (cpm/µCi).
Q19: What is the "photopeak"?
A: The peak in the energy spectrum that corresponds to the full energy of the
emitted gamma photon.
Q20: What causes a "Compton scatter" event?
A: A gamma photon interacts with an outer-shell electron, transferring some of
its energy and changing direction. This results in a lower-energy photon that can
degrade image quality.
Q21: How does a well counter differ from a gamma camera?
A: A well counter is a non-imaging detector with a high geometric efficiency
(nearly 4π) used for counting small samples, while a gamma camera is an
imaging device.
Q22: What is the purpose of a dose calibrator?
A: To measure the activity of a radiopharmaceutical before administration to a
patient.
Q23: What is a "constancy" test for a dose calibrator?
A: A daily check using a long-lived reference source (e.g., Cs-137 or Co-57) to
ensure the calibrator's response has not drifted over time.
Q24: What does a "linearity" test check on a dose calibrator?
A: It verifies that the dose calibrator's reading is accurate across a wide range of
activities.
Q25: What is a "geometry" test for a dose calibrator?
A: It checks that the measured activity is independent of the sample's volume
and position within the calibrator.
Q26: What is the purpose of a survey meter in nuclear medicine?
A: To measure radiation exposure rates (e.g., mR/hr) for area surveys and to
check for contamination.
Q27: What is the difference between a Geiger-Mueller (GM) counter and
an ionization chamber?
A: A GM counter is very sensitive and used for detecting low levels of radiation
(e.g., contamination surveys), while an ionization chamber is less sensitive but
Q&A|| LATEST UPDATE 2026
Section 1: Physics & Instrumentation (40 Questions)
Q1: What is the primary purpose of a photomultiplier tube (PMT) in a
gamma camera?
A: To convert the weak light scintillations from the crystal into a measurable
electrical signal and amplify it.
Q2: Define "energy resolution" in the context of a gamma camera.
A: It is the ability of the detector to distinguish between two photopeaks of
different energies. It is typically expressed as the Full Width at Half Maximum
(FWHM) of a photopeak.
Q3: What is the function of a collimator?
A: To define the field of view and spatially localize the source of gamma
emissions by only allowing photons traveling in a specific direction to reach the
detector crystal.
Q4: Which collimator type provides the highest sensitivity but the lowest
resolution?
A: A high-sensitivity (or low-resolution) collimator. It has wider holes and
thinner septa.
Q5: A technologist uses a 140 keV photopeak for a Technetium-99m scan.
What is the acceptable energy window?
A: A 20% window, which is calculated as 140 keV ± 10% (126 keV to 154
keV).
Q6: What is the purpose of the pulse height analyzer (PHA)?
A: To select only those electrical pulses that fall within the preselected energy
window, thereby rejecting scattered photons.
Q7: What is "dead time" in a gamma camera?
A: The time during which the system is processing a pulse and is unable to
process another event. This leads to count loss at high activities.
,Q8: Explain the difference between a paralyzable and a non-paralyzable
dead time model.
A: In a paralyzable model, every event (even those not counted) extends the
dead time. In a non-paralyzable model, the dead time is fixed for each recorded
event.
Q9: What is the purpose of a uniformity flood test?
A: To check the intrinsic or extrinsic uniformity of the gamma camera's
response to a uniform source of radioactivity. It helps detect crystal defects,
PMT issues, or collimator damage.
Q10: What is the difference between intrinsic and extrinsic uniformity
testing?
A: Intrinsic uniformity is tested without a collimator, assessing the crystal and
PMT system. Extrinsic uniformity is tested with a collimator in place, assessing
the entire imaging system.
Q11: What does a "bar phantom" test?
A: It tests the spatial resolution of the gamma camera system.
Q12: In SPECT imaging, what is the purpose of a "center of rotation"
(COR) calibration?
A: To correct for any misalignment between the mechanical axis of rotation and
the electronic center of the gamma camera's field of view.
Q13: What are the main advantages of PET imaging over SPECT imaging?
A: Higher sensitivity, better spatial resolution, and the ability to perform
accurate attenuation correction and absolute quantification of activity.
Q14: What is the physical principle behind Positron Emission Tomography
(PET)?
A: Annihilation of a positron with an electron, producing two 511 keV photons
emitted at approximately 180 degrees to each other.
Q15: What is a PET detector typically made of?
A: A scintillation crystal (e.g., LSO, BGO, or LYSO) coupled to a
photodetector (e.g., PMT or SiPM).
Q16: What is "time-of-flight" (TOF) PET?
A: A PET technique that measures the small difference in arrival time of the
two annihilation photons to more precisely localize the annihilation event along
the line of response, improving image quality.
Q17: What is the purpose of a "septa" in a PET scanner?
A: In 2D PET, septa are used to reduce the detection of scattered and random
, coincidences from outside the imaging plane. Modern 3D PET scanners do not
have septa.
Q18: Define "sensitivity" of a gamma camera.
A: The efficiency with which the camera detects gamma rays. It is typically
measured in counts per minute per microcurie (cpm/µCi).
Q19: What is the "photopeak"?
A: The peak in the energy spectrum that corresponds to the full energy of the
emitted gamma photon.
Q20: What causes a "Compton scatter" event?
A: A gamma photon interacts with an outer-shell electron, transferring some of
its energy and changing direction. This results in a lower-energy photon that can
degrade image quality.
Q21: How does a well counter differ from a gamma camera?
A: A well counter is a non-imaging detector with a high geometric efficiency
(nearly 4π) used for counting small samples, while a gamma camera is an
imaging device.
Q22: What is the purpose of a dose calibrator?
A: To measure the activity of a radiopharmaceutical before administration to a
patient.
Q23: What is a "constancy" test for a dose calibrator?
A: A daily check using a long-lived reference source (e.g., Cs-137 or Co-57) to
ensure the calibrator's response has not drifted over time.
Q24: What does a "linearity" test check on a dose calibrator?
A: It verifies that the dose calibrator's reading is accurate across a wide range of
activities.
Q25: What is a "geometry" test for a dose calibrator?
A: It checks that the measured activity is independent of the sample's volume
and position within the calibrator.
Q26: What is the purpose of a survey meter in nuclear medicine?
A: To measure radiation exposure rates (e.g., mR/hr) for area surveys and to
check for contamination.
Q27: What is the difference between a Geiger-Mueller (GM) counter and
an ionization chamber?
A: A GM counter is very sensitive and used for detecting low levels of radiation
(e.g., contamination surveys), while an ionization chamber is less sensitive but
