NUCLEAR MEDICINE BOARD REVIEW INSTRUMENTATION EXAM QUESTIONS &
ANSWERS | LATEST ALREADY GRADED A+ UPDATE 2026|2027!!
1.
Which of the following collimators would be best for imaging a thyroid uptake
scan using I-123?
A. Low-energy high-resolution (LEHR)
B. High-energy general-purpose (HEGP)
C. Medium-energy parallel hole
D. Pinhole
Answer: D. Pinhole
Rationale: The pinhole collimator provides high-resolution images for small
organs close to the detector, such as the thyroid. While LEHR is common for I-
123, pinhole allows magnification and greater detail, which is particularly useful
for thyroid morphology.
2.
What is the primary purpose of a sodium iodide (NaI) crystal in gamma cameras?
A. Amplify signal strength
B. Detect and convert gamma photons to light
C. Measure electrical current
D. Block scatter radiation
Answer: B. Detect and convert gamma photons to light
Rationale: Sodium iodide (NaI) crystals doped with thallium convert gamma
radiation into visible light flashes (scintillations). Photomultiplier tubes then
convert these flashes into electrical signals for imaging.
3.
The resolving ability of a gamma camera is most dependent on which factor?
A. Collimator design
B. Crystal thickness
C. PMT voltage
D. Camera housing
,Answer: A. Collimator design
Rationale: Collimators dictate spatial resolution and sensitivity. A thinner septa
and smaller hole diameter provide higher resolution but lower sensitivity. Crystal
thickness impacts energy resolution but collimators primarily control spatial
resolution.
4.
What is the function of a photomultiplier tube (PMT) in a gamma camera?
A. Focus gamma photons onto the crystal
B. Convert light photons into an amplified electrical signal
C. Collimate radiation before detection
D. Reduce patient dose
Answer: B. Convert light photons into an amplified electrical signal
Rationale: PMTs detect the weak light flashes from the crystal and convert them
into measurable electrical pulses by multiplying electrons through dynodes,
allowing signal amplification for image creation.
5.
Which imaging artifact is most commonly caused by non-uniformity of the gamma
camera crystal?
A. Star artifact
B. Cold spots
C. Ring artifact
D. Edge packing
Answer: B. Cold spots
Rationale: Non-uniformity in crystal response leads to areas of decreased
sensitivity, appearing as cold spots in images. Flood field quality control detects
these problems early.
6.
What does the energy window setting on a gamma camera control?
A. Voltage applied to PMTs
B. Scatter rejection by selecting acceptable photon energy range
C. Collimator sensitivity
D. Time resolution
Answer: B. Scatter rejection by selecting acceptable photon energy range
Rationale: The energy window defines which gamma photons (within a specified
keV range) are accepted. This helps reject scatter photons outside the primary
, photopeak, improving image quality.
7.
A thicker NaI crystal will result in:
A. Higher spatial resolution
B. Lower energy resolution but better detection efficiency
C. Improved scatter rejection
D. Reduced sensitivity
Answer: B. Lower energy resolution but better detection efficiency
Rationale: Thick crystals increase detection efficiency (catching more photons)
but spread light signals more, decreasing energy resolution and image sharpness.
8.
The photopeak in a gamma camera energy spectrum corresponds to:
A. Scatter photons
B. The full energy deposition of a gamma photon in the crystal
C. Electrical noise
D. Collimator septal penetration
Answer: B. The full energy deposition of a gamma photon in the crystal
Rationale: The photopeak represents events where the gamma photon deposits
its full energy (photoelectric effect), allowing for accurate imaging and peak
windowing.
9.
Daily uniformity quality control for a gamma camera is performed using:
A. Co-57 flood source
B. I-131 capsule
C. Lead bar phantom
D. Dose calibrator
Answer: A. Co-57 flood source
Rationale: A Co-57 flood source provides uniform photon distribution and long
half-life, making it ideal for daily gamma camera uniformity checks.
10.
Which factor most influences system sensitivity in nuclear medicine imaging?
A. Collimator hole diameter
B. Crystal resolution
C. PMT number
ANSWERS | LATEST ALREADY GRADED A+ UPDATE 2026|2027!!
1.
Which of the following collimators would be best for imaging a thyroid uptake
scan using I-123?
A. Low-energy high-resolution (LEHR)
B. High-energy general-purpose (HEGP)
C. Medium-energy parallel hole
D. Pinhole
Answer: D. Pinhole
Rationale: The pinhole collimator provides high-resolution images for small
organs close to the detector, such as the thyroid. While LEHR is common for I-
123, pinhole allows magnification and greater detail, which is particularly useful
for thyroid morphology.
2.
What is the primary purpose of a sodium iodide (NaI) crystal in gamma cameras?
A. Amplify signal strength
B. Detect and convert gamma photons to light
C. Measure electrical current
D. Block scatter radiation
Answer: B. Detect and convert gamma photons to light
Rationale: Sodium iodide (NaI) crystals doped with thallium convert gamma
radiation into visible light flashes (scintillations). Photomultiplier tubes then
convert these flashes into electrical signals for imaging.
3.
The resolving ability of a gamma camera is most dependent on which factor?
A. Collimator design
B. Crystal thickness
C. PMT voltage
D. Camera housing
,Answer: A. Collimator design
Rationale: Collimators dictate spatial resolution and sensitivity. A thinner septa
and smaller hole diameter provide higher resolution but lower sensitivity. Crystal
thickness impacts energy resolution but collimators primarily control spatial
resolution.
4.
What is the function of a photomultiplier tube (PMT) in a gamma camera?
A. Focus gamma photons onto the crystal
B. Convert light photons into an amplified electrical signal
C. Collimate radiation before detection
D. Reduce patient dose
Answer: B. Convert light photons into an amplified electrical signal
Rationale: PMTs detect the weak light flashes from the crystal and convert them
into measurable electrical pulses by multiplying electrons through dynodes,
allowing signal amplification for image creation.
5.
Which imaging artifact is most commonly caused by non-uniformity of the gamma
camera crystal?
A. Star artifact
B. Cold spots
C. Ring artifact
D. Edge packing
Answer: B. Cold spots
Rationale: Non-uniformity in crystal response leads to areas of decreased
sensitivity, appearing as cold spots in images. Flood field quality control detects
these problems early.
6.
What does the energy window setting on a gamma camera control?
A. Voltage applied to PMTs
B. Scatter rejection by selecting acceptable photon energy range
C. Collimator sensitivity
D. Time resolution
Answer: B. Scatter rejection by selecting acceptable photon energy range
Rationale: The energy window defines which gamma photons (within a specified
keV range) are accepted. This helps reject scatter photons outside the primary
, photopeak, improving image quality.
7.
A thicker NaI crystal will result in:
A. Higher spatial resolution
B. Lower energy resolution but better detection efficiency
C. Improved scatter rejection
D. Reduced sensitivity
Answer: B. Lower energy resolution but better detection efficiency
Rationale: Thick crystals increase detection efficiency (catching more photons)
but spread light signals more, decreasing energy resolution and image sharpness.
8.
The photopeak in a gamma camera energy spectrum corresponds to:
A. Scatter photons
B. The full energy deposition of a gamma photon in the crystal
C. Electrical noise
D. Collimator septal penetration
Answer: B. The full energy deposition of a gamma photon in the crystal
Rationale: The photopeak represents events where the gamma photon deposits
its full energy (photoelectric effect), allowing for accurate imaging and peak
windowing.
9.
Daily uniformity quality control for a gamma camera is performed using:
A. Co-57 flood source
B. I-131 capsule
C. Lead bar phantom
D. Dose calibrator
Answer: A. Co-57 flood source
Rationale: A Co-57 flood source provides uniform photon distribution and long
half-life, making it ideal for daily gamma camera uniformity checks.
10.
Which factor most influences system sensitivity in nuclear medicine imaging?
A. Collimator hole diameter
B. Crystal resolution
C. PMT number
