| Abstract | During the past decade, the whole-body counter has evolved as a highly developed, practical system for measuring with accuracy and precision body burdens of internally-deposited gamma-emitting radionuclides. Numerous applications for this system have been made in the field of medical research and diagnosis. There are three basic counting systems based on differing detectors and geometries: the single crystal detector, the multicrystal detector and the liquid scintillation counter. Of these, the most widely used system employs a single fixed crystal (8"×4") with "standard-chair" geometry, in a shield of 6" of steel. Whole-body counting systems require that a high signal-to-noise ratio be attained for the detection of low levels of in-vivo activity. This ratio depends on the performance of each of the components in the system: the detector, the electronics, the shielding and the patient-detector geometry. Each of these is discussed in some detail. The minimum detectable activity under standard counting conditions for a single NaI detector systems is approximately 1 mμc. |
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