PET 2026 Exam Prep: Positron Emission
Tomography Practice Questions with Answer
Rationales Radiopharmaceuticals | Image
Acquisition | Quality Control | Oncology
Protocols | Clinical Review
SECTION 1: RADIOPHARMACEUTICALS (Questions 1–26)
1. Which type of radioactive decay is fundamental to positron emission
tomography (PET)?
A) Alpha decay
B) Beta-minus decay
C) Beta-plus decay
D) Gamma emission
Correct Answer: C) Beta-plus decay
Rationale: PET imaging relies on beta-plus decay (positron emission), where a
proton in the nucleus is converted to a neutron, emitting a positron and a neutrino.
The emitted positron travels a short distance in tissue before annihilating with an
electron, producing two 511 keV gamma photons.
2. What is the energy of each annihilation photon produced when a positron
encounters an electron?
A) 140 keV
B) 364 keV
C) 511 keV
D) 1022 keV
Correct Answer: C) 511 keV
,Rationale: Each annihilation event produces two 511 keV photons emitted in
opposite directions (180° apart). The 511 keV energy corresponds to the rest mass
of the electron (0.511 MeV). This back-to-back emission is the basis for
coincidence detection in PET.
3. What is the half-life of Fluorine-18 (F-18)?
A) 20 minutes
B) 68 minutes
C) 110 minutes
D) 13 hours
Correct Answer: C) 110 minutes
Rationale: F-18 has a physical half-life of approximately 109.7 minutes
(approximately 110 minutes). This relatively long half-life (compared to other PET
isotopes) allows for transport from a central cyclotron facility to imaging sites and
permits delayed imaging protocols.
4. Which PET radionuclide has the shortest half-life?
A) F-18
B) C-11
C) N-13
D) O-15
Correct Answer: D) O-15
Rationale: The half-lives of common PET radionuclides are: F-18 (110 minutes),
C-11 (20 minutes), N-13 (10 minutes), and O-15 (2 minutes). O-15 has the shortest
half-life, requiring an on-site cyclotron for production and immediate use.
5. What is the primary advantage of F-18 FDG for oncological PET imaging?
A) It has the longest half-life of all PET tracers
,B) It is a glucose analog that accumulates in cells with high metabolic activity
C) It requires no cyclotron for production
D) It emits lower-energy photons than other tracers
Correct Answer: B) It is a glucose analog that accumulates in cells with high
metabolic activity
Rationale: F-18 FDG (fluorodeoxyglucose) is a glucose analog that is transported
into cells and phosphorylated but cannot undergo further metabolism, becoming
trapped. Cancer cells typically have increased glucose metabolism (Warburg
effect), leading to increased FDG accumulation.
6. Which radiopharmaceutical is used for imaging prostate cancer with PET?
A) F-18 FDG
B) Ga-68 PSMA
C) F-18 NaF
D) C-11 Methionine
Correct Answer: B) Ga-68 PSMA
Rationale: Ga-68 PSMA (prostate-specific membrane antigen) is a PET
radiopharmaceutical that targets PSMA, which is overexpressed in prostate cancer
cells. It has demonstrated superior sensitivity and specificity for prostate cancer
detection compared to conventional imaging.
7. What is the mechanism of uptake for Ga-68 DOTATATE?
A) Glucose metabolism
B) Somatostatin receptor binding
C) Amino acid transport
D) Bone turnover
Correct Answer: B) Somatostatin receptor binding
, Rationale: Ga-68 DOTATATE binds to somatostatin receptors (SSTR2) that are
overexpressed on neuroendocrine tumors. This allows for sensitive detection and
staging of well-differentiated neuroendocrine tumors.
8. What is the recommended fasting period before an FDG PET/CT scan?
A) 2 hours
B) 4 hours
C) At least 6 hours
D) 12 hours
Correct Answer: C) At least 6 hours
Rationale: Patients should fast for at least 6 hours before FDG PET/CT to ensure
low blood glucose levels, which minimizes competitive inhibition of FDG uptake
by endogenous glucose. Blood glucose levels should be below 200 mg/dL before
injection.
9. What is the typical administered activity of F-18 FDG for adult oncology
PET/CT?
A) 37–74 MBq (1–2 mCi)
B) 185–370 MBq (5–10 mCi)
C) 370–740 MBq (10–20 mCi)
D) 740–1,110 MBq (20–30 mCi)
Correct Answer: C) 370–740 MBq (10–20 mCi)
Rationale: The recommended intravenous dose of F-18 FDG for adults ranges
from 370 to 740 MBq (10–20 mCi). For children, the dose is 4–5 MBq/kg. Dosing
may be adjusted based on patient weight and scanner sensitivity.
10. What is the purpose of a radiochemical purity test for PET
radiopharmaceuticals?
Tomography Practice Questions with Answer
Rationales Radiopharmaceuticals | Image
Acquisition | Quality Control | Oncology
Protocols | Clinical Review
SECTION 1: RADIOPHARMACEUTICALS (Questions 1–26)
1. Which type of radioactive decay is fundamental to positron emission
tomography (PET)?
A) Alpha decay
B) Beta-minus decay
C) Beta-plus decay
D) Gamma emission
Correct Answer: C) Beta-plus decay
Rationale: PET imaging relies on beta-plus decay (positron emission), where a
proton in the nucleus is converted to a neutron, emitting a positron and a neutrino.
The emitted positron travels a short distance in tissue before annihilating with an
electron, producing two 511 keV gamma photons.
2. What is the energy of each annihilation photon produced when a positron
encounters an electron?
A) 140 keV
B) 364 keV
C) 511 keV
D) 1022 keV
Correct Answer: C) 511 keV
,Rationale: Each annihilation event produces two 511 keV photons emitted in
opposite directions (180° apart). The 511 keV energy corresponds to the rest mass
of the electron (0.511 MeV). This back-to-back emission is the basis for
coincidence detection in PET.
3. What is the half-life of Fluorine-18 (F-18)?
A) 20 minutes
B) 68 minutes
C) 110 minutes
D) 13 hours
Correct Answer: C) 110 minutes
Rationale: F-18 has a physical half-life of approximately 109.7 minutes
(approximately 110 minutes). This relatively long half-life (compared to other PET
isotopes) allows for transport from a central cyclotron facility to imaging sites and
permits delayed imaging protocols.
4. Which PET radionuclide has the shortest half-life?
A) F-18
B) C-11
C) N-13
D) O-15
Correct Answer: D) O-15
Rationale: The half-lives of common PET radionuclides are: F-18 (110 minutes),
C-11 (20 minutes), N-13 (10 minutes), and O-15 (2 minutes). O-15 has the shortest
half-life, requiring an on-site cyclotron for production and immediate use.
5. What is the primary advantage of F-18 FDG for oncological PET imaging?
A) It has the longest half-life of all PET tracers
,B) It is a glucose analog that accumulates in cells with high metabolic activity
C) It requires no cyclotron for production
D) It emits lower-energy photons than other tracers
Correct Answer: B) It is a glucose analog that accumulates in cells with high
metabolic activity
Rationale: F-18 FDG (fluorodeoxyglucose) is a glucose analog that is transported
into cells and phosphorylated but cannot undergo further metabolism, becoming
trapped. Cancer cells typically have increased glucose metabolism (Warburg
effect), leading to increased FDG accumulation.
6. Which radiopharmaceutical is used for imaging prostate cancer with PET?
A) F-18 FDG
B) Ga-68 PSMA
C) F-18 NaF
D) C-11 Methionine
Correct Answer: B) Ga-68 PSMA
Rationale: Ga-68 PSMA (prostate-specific membrane antigen) is a PET
radiopharmaceutical that targets PSMA, which is overexpressed in prostate cancer
cells. It has demonstrated superior sensitivity and specificity for prostate cancer
detection compared to conventional imaging.
7. What is the mechanism of uptake for Ga-68 DOTATATE?
A) Glucose metabolism
B) Somatostatin receptor binding
C) Amino acid transport
D) Bone turnover
Correct Answer: B) Somatostatin receptor binding
, Rationale: Ga-68 DOTATATE binds to somatostatin receptors (SSTR2) that are
overexpressed on neuroendocrine tumors. This allows for sensitive detection and
staging of well-differentiated neuroendocrine tumors.
8. What is the recommended fasting period before an FDG PET/CT scan?
A) 2 hours
B) 4 hours
C) At least 6 hours
D) 12 hours
Correct Answer: C) At least 6 hours
Rationale: Patients should fast for at least 6 hours before FDG PET/CT to ensure
low blood glucose levels, which minimizes competitive inhibition of FDG uptake
by endogenous glucose. Blood glucose levels should be below 200 mg/dL before
injection.
9. What is the typical administered activity of F-18 FDG for adult oncology
PET/CT?
A) 37–74 MBq (1–2 mCi)
B) 185–370 MBq (5–10 mCi)
C) 370–740 MBq (10–20 mCi)
D) 740–1,110 MBq (20–30 mCi)
Correct Answer: C) 370–740 MBq (10–20 mCi)
Rationale: The recommended intravenous dose of F-18 FDG for adults ranges
from 370 to 740 MBq (10–20 mCi). For children, the dose is 4–5 MBq/kg. Dosing
may be adjusted based on patient weight and scanner sensitivity.
10. What is the purpose of a radiochemical purity test for PET
radiopharmaceuticals?
