Tomographic effect by coded apertures

Besides the transverse axial tomographic emission methods for gamma emitters or positrons, nuclear imaging methods by coding have developed which make it possible to have access to longitudinal tomographies. Different versions were proposed as early as 1972 and may be classed into two main categories according to the number of recordings necessary at the second stage of the process: the decoding. 1 - Those which consist in obtaining one only coded image operating on the principle of the geometrical optic lens (or of holography). 2 - Those which, on the contrary, require several recordings which are classed under the term 'transmittance variation apertures' among which may be noted the methods of Chang, Akcasu (1974) and Tanaka (1975) as well as a sequential method developed here. The theoretical and practical possibilities of each of these two categories are examined in detail first, then the method using a unique annular aperture developed and applied in the radioisotope department of the Cochin hospital is presented