Free Nuclear Medicine Exam Questions That Helps Candidates Pass

Comprehensive and Detailed Explanation: The annual occupational dose limit for the lens of the eye is 150 mSv (15 rem). The whole-body effective-dose limit is 50 mSv, and the extremity limit is 500 mSv. These limits are set to prevent deterministic effects (cataracts for the lens) while controlling stochastic risk. Nuclear medicine technologists can receive measurable eye dose when handling unshielded vials or working near high-activity sources without proper eye protection or distance. Lead glasses or face shields may be warranted in high-workload laboratories. Monitoring is usually performed with a whole-body dosimeter worn at collar level; dedicated eye dosimeters are used when indicated. Compliance with these limits and ALARA principles is mandatory.

Comprehensive and Detailed Explanation: A new, persistent cold spot on a daily flood most often indicates photomultiplier-tube failure, a decoupling of a PMT from the crystal, or crystal damage. Continuing to use the camera can produce artifacts that mimic pathology or obscure real lesions. The technologist should first confirm the finding with a repeat flood (both intrinsic and extrinsic if possible). If the defect remains, the camera must be taken out of clinical service and the service engineer notified. Simply applying a previous correction map will not correct a new hardware failure. Documentation of the problem and the action taken is required. Prompt recognition and response protect patients from nondiagnostic or misleading studies.

Comprehensive and Detailed Explanation: Thallium-201 is a potassium analogue and is transported into myocytes primarily by the Na+/K+ ATPase pump. Uptake is therefore proportional to both regional blood flow and the integrity of the myocyte membrane. This property allows assessment of perfusion and viability. Passive diffusion contributes to a lesser extent. Phagocytosis and chemisorption are mechanisms for other agents. Technologists must understand this mechanism to appreciate why Tl-201 redistributes and why it remains useful for viability studies even though Tc-99m agents are preferred for routine perfusion imaging because of superior image quality and lower radiation dose.

Comprehensive and Detailed Explanation: Fluorine-18 has a physical half-life of approximately 109–110 minutes. This short half-life necessitates efficient production, transport, and scheduling of PET studies. Decay corrections must be applied carefully when calculating residual activity or when comparing sequential scans. The half-life is long enough to allow 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 to maximize count statistics while remaining within the prescribed activity range.

Comprehensive and Detailed Explanation: Tc-99m sulfur colloid particles are removed from the blood by phagocytosis by reticuloendothelial cells (Kupffer cells) of the liver and by macrophages in the spleen and bone marrow. This mechanism is the basis for liver-spleen imaging and for detecting colloid shift in portal hypertension. Hepatocytes take up IDA compounds; glomerular filtration clears DTPA; chemisorption binds diphosphonates to bone. Technologists must understand this biodistribution to recognize normal variants, technical artifacts related to particle size, and pathologic patterns such as focal defects or colloid shift.