Free Nuclear Medicine Exam Questions That Helps Candidates Pass

Comprehensive and Detailed Explanation: LEHR collimators have smaller holes and longer septa than LEGP collimators, providing superior spatial resolution at the cost of reduced sensitivity. They are preferred when fine detail is important (e.g., bone SPECT, pediatric imaging, or cardiac SPECT when count rates permit). LEGP collimators are chosen when higher sensitivity is needed. Technologists must select the collimator appropriate for the clinical question and available activity. Using the wrong collimator can either degrade resolution or produce images with inadequate counts and increased noise.

Comprehensive and Detailed Explanation: Most Tc-99m MDP (and HDP) kits are supplied as lyophilized vials containing the ligand and stannous reductant. The technologist simply adds the appropriate volume and activity of Tc-99m sodium pertechnetate and gently mixes. No boiling is required (unlike some sestamibi kits). Adding reagents in the wrong order or using excessive volume can reduce labeling efficiency. Package-insert instructions must be followed exactly regarding maximum activity, minimum and maximum volumes, and incubation time. After preparation, radiochemical purity testing may be required. Incorrect preparation can result in free pertechnetate (stomach and thyroid visualization) or colloidal impurities (liver and spleen uptake), both of which degrade bone-scan quality and increase non-target radiation dose.

Comprehensive and Detailed Explanation: In the photoelectric effect the entire energy of the incident photon is absorbed by an orbital electron, resulting in full energy deposition in the crystal and appearance of the photopeak. Compton scattering deposits only part of the energy and produces the continuum below the photopeak. Pair production occurs only above 1.022 MeV. Understanding the origin of the photopeak allows technologists to set energy windows correctly, recognize the effects of scatter, and interpret changes in energy resolution that may indicate crystal or electronics problems.

Comprehensive and Detailed Explanation: Fluorine-18 has a physical half-life of approximately 109–110 minutes. This short half-life requires efficient production, rapid transport, and careful scheduling of PET studies. Decay corrections must be applied accurately when calculating residual activity or comparing sequential scans. The half-life is long enough to permit synthesis of FDG and delivery to imaging centers within a reasonable radius of a cyclotron, yet short enough to limit patient radiation dose. Technologists working with PET must be proficient in rapid decay calculations and in coordinating injection and imaging times.

Comprehensive and Detailed Explanation: High-radiation areas are posted and access-controlled because an individual could receive a dose exceeding 1 mSv (100 mrem) in 1 hour at 30 cm from the source. Restricting entry, using interlocks or visual alarms when required, and limiting stay times are fundamental radiation-protection measures. Only trained personnel with appropriate dosimetry should enter, and the radiation safety officer must approve or supervise work in such areas. In nuclear medicine this situation most often arises after a major spill or during handling of high-activity therapy sources. Proper control prevents accidental overexposure and is a clear regulatory requirement.