1. In a computed tomography apparatus having an X-ray source and a radiation detector for conducting a scan of subject by rotating around said subject to generate a continuous measurement data stream while irradiating said subject from different rotational angles, an image reconstruction computer having a computing capacity, and a monitor on which an image of said subject reconstructed by said image reconstruction computer is displayed, the improvement of a method for reconstructing said image of said subject in said image reconstruction computer comprising the steps of: taking successive data segments from said continuous measurement data stream, said data segments respectively comprising data generated beginning from different starting rotation angles of said X-ray source; using said data segments for respective sub-scan image reconstructions in said image reconstruction computer; and selecting the respective starting rotational angles for said data segments according to a reconstruction grid for said sub-scan reconstructions which substantially maximally utilizes said computing capacity of said image reconstruction computer.