Free Nuclear Medicine Exam Questions That Helps Candidates Pass

Comprehensive and Detailed Explanation: Daily intrinsic or extrinsic flood images are acquired to verify that the camera’s response remains uniform across the field of view. A new cold or hot area, or a significant change in quantitative uniformity values, indicates a problem such as photomultiplier-tube failure or crystal damage. Continuing to use a non-uniform camera can produce artifacts that mimic pathology. The flood is inspected visually and quantitatively; results are documented. If the flood is unacceptable, the camera is removed from service until repaired. This daily check is one of the most important quality-control procedures performed by nuclear medicine technologists.

Comprehensive and Detailed Explanation: After intravenous injection of Tc-99m sulfur colloid, imaging is typically begun 10–15 minutes later, once the particles have been cleared from the blood by the reticuloendothelial system. Earlier imaging may show residual blood-pool activity; much later imaging is unnecessary because the distribution is stable. Multiple views (anterior, posterior, laterals, and obliques) are obtained, and SPECT may be added. Technologists must ensure that the patient is properly positioned and that the count density is adequate. Recognition of normal variants (e.g., colloid shift to spleen and bone marrow in portal hypertension) and technical artifacts is essential for high-quality studies.

Comprehensive and Detailed Explanation: An abrupt rise in background counts most often indicates radioactive contamination inside or near the well. Residual activity from previous samples, a contaminated tube, or external contamination of the detector can all elevate background. Background must be measured and subtracted for accurate sample counting (e.g., thyroid uptakes, wipe tests, or blood volumes). If background is elevated, the well should be cleaned, resurveyed, and rechecked before further measurements. Technologists must count background regularly and maintain a clean counting area. Ignoring elevated background introduces systematic errors into quantitative results and may mask true contamination on wipe tests.

Comprehensive and Detailed Explanation: Center-of-rotation calibration determines any offset between the mechanical axis of the gantry and the electronic center of the detector matrix. Even small misalignments produce blurring and circular artifacts in reconstructed SPECT images. The calibration is performed with a point or line source and is required at regular intervals or after service. The resulting correction is applied during reconstruction. Uniformity maps, energy peaking, and decay correction are separate processes. Technologists must verify that the appropriate COR file is selected for the collimator and orbit type being used. Failure to maintain accurate COR calibration is a common source of preventable SPECT artifacts.

Comprehensive and Detailed Explanation: Tc-99m DMSA binds to the proximal tubular cells of the renal cortex and provides high-resolution images of cortical structure. It is the agent of choice for detecting pyelonephritic scarring, evaluating differential function, and assessing congenital anomalies. DTPA and MAG3 are cleared more rapidly and are preferred for dynamic functional studies. Imaging is performed 2–4 hours after injection, often with SPECT. Technologists must ensure adequate hydration, correct timing, and high-resolution collimation. Accurate DMSA imaging directly influences clinical decisions regarding antibiotic prophylaxis or surgical intervention in children with recurrent urinary-tract infections.