Abstract: A detector detects gamma-rays emitted from inside an imaging region. An acquisition unit acquires a plurality of first projection data sets associated with a plurality of projection angles via the detector. An attenuation-correction unit attenuation-correct the plurality of first projection data sets based on a first CT image associated with the imaging region to generate a plurality of second projection data sets associated with the plurality of projection angles. An index calculation unit calculates an index based on the plurality of second projection data sets. The index is corresponding to a degree of positional offset between the imaging region at the time of acquisition of a plurality of third projection data sets associated with the first CT image and the imaging region at the time of acquisition of the plurality of first projection data sets.

Abstract: A SPECT apparatus for forming a radioisotope distribution topographic image of an object, in which a detector such as a fan beam collomator detects fan beam shaped gamma ray emitted from a radioisotope given to the object to provide fan beam data, while a scanner causes relative rotation between the object and the detecter, and a data collector collects the fan beam data, and in which a data converter successively converts the fan beam data into parallel beam data during the relative rotation, and a reconstructor reconstructs a tomographic image from the parallel beam data. The fan beam data having a first matrix size and a first angle may be converted into the parallel beam data having a second matrix size and a second angle which are different from the first matrix size and the first angle, respectively.