NMTCB Pharmaceutical & Radiopharmaceutical Agents 5 — Questions and Answers
Question 1: Which radiopharmaceutical is used to image somatostatin receptor-positive neuroendocrine tumors (NETs)?
- Tc-99m MIBI
- Ga-68 DOTATATE (Correct answer)
- F-18 NaF
- Tc-99m DMSA
Correct answer: Ga-68 DOTATATE
Ga-68 DOTATATE binds with high affinity to somatostatin receptor subtype 2 (SSTR2), which is overexpressed on most neuroendocrine tumors.
Question 2: What is the primary mechanism of Tc-99m tetrofosmin (Myoview) myocardial uptake?
- Sodium-potassium ATPase pump binding
- Passive redistribution driven by mitochondrial membrane potential (Correct answer)
- Receptor-mediated binding to cardiac myosin
- Active sodium-calcium exchanger transport
Correct answer: Passive redistribution driven by mitochondrial membrane potential
Tc-99m tetrofosmin is a lipophilic cationic complex that accumulates in mitochondria of viable myocardial cells driven by the large negative mitochondrial membrane potential.
Question 3: Tc-99m DMSA (dimercaptosuccinic acid) is most commonly used for imaging of the:
- Liver and spleen
- Renal cortex to detect scarring or functional cortical mass (Correct answer)
- Thyroid gland
- Adrenal glands
Correct answer: Renal cortex to detect scarring or functional cortical mass
Tc-99m DMSA binds to renal tubular cells and provides a static image of the renal cortex, making it ideal for detecting cortical scars and measuring differential renal function.
Question 4: Which statement about In-111 pentetreotide (OctreoScan) is correct?
- It targets dopamine receptors on pituitary tumors
- It is a somatostatin analogue that images neuroendocrine tumors expressing SSTR (Correct answer)
- It requires patient fasting for 24 hours due to liver metabolism
- It emits positrons and requires a PET scanner
Correct answer: It is a somatostatin analogue that images neuroendocrine tumors expressing SSTR
In-111 pentetreotide is a radiolabeled octreotide analogue that binds somatostatin receptors (primarily SSTR2) on neuroendocrine tumors for planar/SPECT imaging.
Question 5: What is the maximum recommended number of Tc-99m MAA particles to inject for a lung perfusion scan in a patient with severe pulmonary hypertension?
- 600,000 particles
- 200,000 particles
- 100,000 particles or fewer (Correct answer)
- 400,000 particles
Correct answer: 100,000 particles or fewer
In severe pulmonary hypertension, the number of MAA particles should be reduced to 100,000 or fewer to minimize the risk of further compromising the reduced pulmonary capillary bed.
Question 6: Ra-223 dichloride (Xofigo) treats castration-resistant prostate cancer with bone metastases because radium-223:
- Emits gamma rays that destroy cancer cells at a distance
- Acts as a calcium analogue and deposits in bone, emitting alpha particles with short range (Correct answer)
- Is taken up by prostate-specific membrane antigen (PSMA)
- Binds to androgen receptors in bone metastases
Correct answer: Acts as a calcium analogue and deposits in bone, emitting alpha particles with short range
Ra-223 mimics calcium, incorporates into bone matrix at osteoblastic metastases, and emits high-LET alpha particles with a very short range (~2-10 cell diameters), minimizing marrow toxicity.
Question 7: Which radiopharmaceutical is used to assess renal tubular secretion (effective renal plasma flow, ERPF)?
- Tc-99m DTPA
- Tc-99m MAG3 (mercaptoacetyltriglycine) (Correct answer)
- Tc-99m DMSA
- Tc-99m glucoheptonate
Correct answer: Tc-99m MAG3 (mercaptoacetyltriglycine)
Tc-99m MAG3 is secreted by proximal renal tubules (like PAH), making it ideal for measuring ERPF and evaluating renal tubular function, especially in patients with poor GFR.
NMTCB Pharmaceutical & Radiopharmaceutical Agents 5
Which radiopharmaceutical is used to image somatostatin receptor-positive neuroendocrine tumors (NETs)?