Measurement of Radioisotope Uptake in Body Organs by Area Scanning

This paper reviews methods for the measurement of radioactivity in body organs based on the analysis of scintigraphic data and their applications. The physical problems arising in the use of scintigraphic systems for such measurements are compared with those arising in the use of non-imaging fixed detectors. Since the inverse square law effect is to a large extent absent with scintigraphic systems, the dependence of the sensitivity of such a system on depth of source in the body is due mainly to attenuation of radiation in the tissues; this may be largely overcome by the use of a system with two opposed detectors. Location of the organ presents no problem in scintigraphy provided that a suitable organ-specific radiopharmaceutical is available. Delineation of the organ depends on the resolution of the system, and in particular on the dependence of resolution on depth of source. Again, this dependence may be largely overcome by the use of a system with two opposed detectors. The problem of overlapping of the images of closely adjacent organs is briefly discussed. Techniques for the calibration of measurements based on the analysis of scintigraphic data are described. Corrections must usually be applied for the overall background and for variation in body thickness over the area as well as for physical decay of the radioisotope. These corrections can most conveniently be made by computer analysis of the data. Various applications of the methods are described. (author)