THE NEW TECHNIQUES OF SCINTIGRAPHIC IMAGING

The purpose of scintigraphic imaging is not to explore the morphology of an organ (or its abnormalities) but rather its functional and metabolic characteristics. It is thus important that a molecular structure (e.g., a hormonal receptor or an antigen) closely linked to the functional activity of an organ or tissue by targeted on its cell surface. Such diagnostic targeting requires the synthesis and labeling of a radiopharmaceutical substance specific for the receptor or antigen in question. It also requires a detection system adapted to count rates and signal-to-background ratios (generally moderate). The synthesis of new radiopharmaceutical agents, a critical stage for the future of nuclear medicine, is a long and often risky process in which success is difficult to foresee. Radiolabeling must be stable in vitro and in vivo, and the radiopharmaceutical must subsequently retain its capability of recognizing the targeted molecule. In endocrinology, the exemplary achievement in this direction has been the synthesis of I-131-6-iodomethylnorcholesterol and I-131-metaiodobenzylquanidine for functional scintigraphy of the adrenal cortex and medulla. Progress in detection equipment has been marked by the development of monophotonic tomoscintigraphy, using gamma cameras with a revolving head to obtain slices in different spatial planes showing the distribution in the organism of the injected radiopharmaceutical agent.