Single‐photon emission CT is one of the most useful techniques in nuclear medicine, wherein a radioisotope material is injected into the body and by external detection of the radiated y‐ray the RI distribution on an arbitrary layer (slice) is reconstructed from the data, permitting visual representation of physiological information. Longitudinal imaging is one of such techniques. The object is regarded as composed of layered RI distributions. From the y‐ray projection data obtained by y‐ray detectors placed parallel to the layer, the RI distribution at each slice is reconstructed. In longitudinal imaging, however, the projection data are observed only along a particular direction and the working range of the detector is restricted, leading to blur and degradation of the reconstructed image. This paper discusses the quality degradation inherent in longitudinal imaging and proposes a reconstruction algorithm which employs the contour information of the object in the reconstruction computation to make correction for the quality. The result of numerical simulation is also reported.
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