Free Nuclear Medicine Exam Questions That Helps Candidates Pass

Comprehensive and Detailed Explanation: Gallium-67 has a physical half-life of approximately 78 hours (3.26 days). It decays by electron capture and emits multiple gamma photons (93, 185, 300, and 394 keV). The relatively long half-life allows imaging at 24, 48, and even 72 hours after injection, which is useful for infection and tumor localization. Technologists must account for this half-life when scheduling delayed views, calculating residual activity, and planning waste storage. Knowledge of the multiple photon energies also guides collimator selection (medium-energy) and energy-window settings. Comparison with shorter-lived agents such as Tc-99m or F-18 highlights why Ga-67 studies require different logistical planning.

Comprehensive and Detailed Explanation: The half-value layer is the thickness of a specified absorber that reduces the intensity of a radiation beam to half its original value. HVL depends on photon energy and the atomic number and density of the material. For 140 keV Tc-99m photons the HVL in lead is approximately 0.3 mm. Technologists use HVL values when selecting syringe and vial shields, evaluating room shielding, and estimating transmission through barriers or patients. Knowledge of HVL also helps interpret survey-meter readings behind lead and explains why thicker shielding is required for higher-energy photons such as those from I-131 or PET radionuclides.

Comprehensive and Detailed Explanation: A constancy reading outside institutional limits (typically ±5 % or ±10 % of the expected decay-corrected value) indicates possible instrument malfunction, contamination, or geometry change. The measurement should be repeated to confirm the finding. If the discrepancy persists, the dose calibrator must be taken out of clinical service until the problem is identified and corrected. Patient doses may not be assayed on an unreliable instrument. Documentation of the failure and subsequent repair is required. This daily check is the primary safeguard against systematic dosing errors and is a core quality-control responsibility of the nuclear medicine technologist.

Comprehensive and Detailed Explanation: Molybdenum-99 has a physical half-life of approximately 66 hours (2.75 days). This relatively long half-life allows Mo-99 to be produced at a reactor or accelerator facility, shipped to radiopharmacies or hospitals, and used as the parent in a Tc-99m generator for about one week. The daughter Tc-99m (half-life 6 hours) is eluted as needed. Iodine-123 has a half-life of about 13 hours, iodine-131 about 8 days, and fluorine-18 about 110 minutes. Accurate knowledge of half-lives is essential for decay corrections, generator scheduling, dose calculations, and determining how long a source remains useful or hazardous. Technologists use decay charts or calculator functions daily when preparing unit doses and when performing quality-control assays.

Comprehensive and Detailed Explanation: Federal regulations require that a written directive for I-131 sodium iodide greater than 1.11 MBq (30 µCi) contain the patient’s name, the radiopharmaceutical, the route of administration, and the prescribed activity or dosage range. The directive must be signed and dated by an authorized user before administration. The technologist must verify patient identity by two independent methods and confirm that the administered activity matches the directive. Any revision must also be signed by the authorized user. Incomplete or missing written directives are a frequent cause of medical-event reports. Strict adherence protects patients and maintains regulatory compliance.