In vivo Identification and Localisation of Radioactive Contamination in the Human Body

Profile measurements were made with a whole-body counter using two scanning NaI detectors, one above and one below the patient couch, equipped with 8 mm slit collimators. Measurements show that by turning the lower collimator slit 45°, the lateral position of a radioactive point source could be determined with an accuracy of about two centimetres by the difference in profile-peak channel between the detectors. This difference was independent of the depth of the source in the phantom. The depth of the point source could be determined by the ratio of the counts in the profile peak from the detectors. This ratio was independent of the lateral displacement. The method can also be used for other radionuclides and an application in radiation protection is to make simultaneous pulse height and profile measurements which makes it possible to apply correction factors for various spatial distributions of the contamination.