To provide a method for forming a diagnostic image by using a nuclear medical gamma-ray camera and to provide a tomographic camera.

A full set of injection data having relatively high resolution of a gantry in one rotation of 360° and transmission data having relatively low resolution are collected by an asymmetric sampling method. The gantry is provided with many radiation detectors and at least one adjustably fitted radiation source. During scanning, the gantry is incrementally rotated around a patient receiving opening at an expected step size through scans P1 to P6 at the first 180° and rotated by P7 or P8 at a half of the expected step size. The gantry is then rotated at the expected step size through scans P8 to P12 at the remaining 180°. The injection data collected in the scans P8 to P12 at the remaining 180° are superimposed in turn on the data collected in the scans at the first 180°.