NMTCB Pharmaceutical & Radiopharmaceutical Agents 2 — Questions and Answers
Question 1: Which radiopharmaceutical is most commonly used for parathyroid localization?
- Tc-99m sestamibi (Correct answer)
- Tc-99m MDP
- Tc-99m DTPA
- Tc-99m sulfur colloid
Correct answer: Tc-99m sestamibi
Tc-99m sestamibi (MIBI) accumulates in mitochondria-rich parathyroid adenoma cells and is the agent of choice for parathyroid scintigraphy.
Question 2: What is the mechanism by which Tc-99m HMPAO crosses the blood-brain barrier?
- Active transport via glucose transporters
- Lipophilicity allows passive diffusion followed by intracellular trapping (Correct answer)
- Receptor-mediated endocytosis
- Pinocytosis through endothelial cells
Correct answer: Lipophilicity allows passive diffusion followed by intracellular trapping
Tc-99m HMPAO is lipophilic and passively crosses the blood-brain barrier, then converts to a hydrophilic form that becomes trapped intracellularly.
Question 3: Which radionuclide used in PET imaging has the longest physical half-life?
- F-18 (110 min) (Correct answer)
- C-11 (20 min)
- N-13 (10 min)
- O-15 (2 min)
Correct answer: F-18 (110 min)
F-18 has the longest half-life among common PET radionuclides at approximately 110 minutes, making it practical for widespread clinical use.
Question 4: I-131 MIBG is used for imaging of which tumor type?
- Hepatocellular carcinoma
- Pheochromocytoma and neuroblastoma (Correct answer)
- Pancreatic adenocarcinoma
- Renal cell carcinoma
Correct answer: Pheochromocytoma and neuroblastoma
MIBG (metaiodobenzylguanidine) is a norepinephrine analogue that accumulates in neuroendocrine tumors such as pheochromocytoma and neuroblastoma.
Question 5: What is the recommended patient preparation before administering I-131 for thyroid therapy?
- High iodine diet for 2 weeks
- Low iodine diet and thyroid hormone withdrawal (Correct answer)
- Administration of potassium perchlorate
- High carbohydrate diet for 48 hours
Correct answer: Low iodine diet and thyroid hormone withdrawal
Patients should follow a low iodine diet and discontinue thyroid hormone medication to maximize TSH stimulation and iodine uptake by thyroid tissue.
Question 6: Ga-67 citrate localizes in infection and inflammation primarily through which mechanism?
- Direct binding to bacterial cell walls
- Association with lactoferrin and transferrin at inflammatory sites (Correct answer)
- Phagocytosis by macrophages only
- Passive diffusion through disrupted capillaries
Correct answer: Association with lactoferrin and transferrin at inflammatory sites
Ga-67 behaves like iron and binds to transferrin in plasma; at inflammatory sites it associates with lactoferrin released by leukocytes and bacterial siderophores.
Question 7: Which quality control test is used to detect free pertechnetate in a Tc-99m-labeled radiopharmaceutical?
- Bacterial endotoxin test
- Instant thin-layer chromatography (ITLC) (Correct answer)
- Aluminum ion breakthrough test
- Osmolality measurement
Correct answer: Instant thin-layer chromatography (ITLC)
ITLC separates free pertechnetate from the bound radiopharmaceutical by chromatographic migration, allowing calculation of radiochemical purity.
NMTCB Pharmaceutical & Radiopharmaceutical Agents 2
Which radiopharmaceutical is most commonly used for parathyroid localization?