Free Nuclear Medicine Exam Questions That Helps Candidates Pass

Comprehensive and Detailed Explanation: Specific activity is the activity per unit mass of the radionuclide or labeled compound (e.g., MBq/mg). High specific activity is important for receptor-binding agents and for preparations in which the mass of carrier must be minimized to avoid pharmacologic effects. Carrier-free preparations have the highest theoretical specific activity. Activity concentration (activity per unit volume) is a different quantity used when drawing doses. Understanding specific activity helps technologists evaluate kit formulations, calculate maximum injectable volumes, and recognize situations in which excess unlabeled ligand could affect biodistribution or image quality.

Comprehensive and Detailed Explanation: Tc-99m macroaggregated albumin (MAA) particles lodge in the pulmonary arterioles in proportion to regional blood flow and are the standard agent for lung perfusion scintigraphy. DTPA aerosol and Xe-133 are used for ventilation imaging. Sulfur colloid is a liver-spleen agent. Technologists must inject MAA slowly with the patient supine, avoid drawing blood into the syringe, and ensure the correct particle number is administered. Multiple views are acquired for comparison with ventilation images in the evaluation of pulmonary embolism.

Comprehensive and Detailed Explanation: Thallium-201 remains a classic agent for viability assessment because it redistributes into hypoperfused but viable myocardium. Protocols include stress-redistribution imaging, rest-redistribution, or reinjection of a second dose of Tl-201 to maximize detection of viable tissue. Tc-99m sestamibi can also be used for viability when combined with nitrate enhancement or compared with perfusion, but Tl-201 has historically been preferred for this specific indication. MAA and Xe-133 are lung agents. Technologists must know the correct timing of redistribution images (typically 3–4 hours or 24 hours) and the reinjection technique. Proper protocol selection directly affects the cardiologist’s decision regarding revascularization.

Comprehensive and Detailed Explanation: Tc-99m macroaggregated albumin (MAA) particles lodge in the pulmonary arterioles in proportion to regional blood flow and are the standard agent for lung perfusion scintigraphy. DTPA aerosol and Xe-133 are used for ventilation imaging. Sulfur colloid is a liver-spleen agent. Technologists must inject MAA slowly with the patient supine, avoid drawing blood into the syringe (which can cause hot spots), and ensure the correct number of particles is administered, especially in patients with pulmonary hypertension or right-to-left shunt.

Comprehensive and Detailed Explanation: When a positron annihilates with an electron, the combined rest mass is converted into two photons of 511 keV each, emitted in nearly opposite directions. These photons are the basis of coincidence detection in PET. The energy is substantially higher than the gamma photons of Tc-99m (140 keV), I-123 (159 keV), or I-131 (364 keV), requiring thicker shielding and different detector design. Technologists working with PET must understand that the high-energy photons produce higher dose rates around patients and sources and that survey meters and shielding must be appropriate for 511 keV radiation. Knowledge of annihilation energy also explains the need for energy windows centered at 511 keV and the origin of random and scatter coincidences.