1. A computer aided image acquisition and diagnosis system for imaging an object and for obtaining a diagnostic image from the projection data thereof, comprising: a selector device for selecting a detection object to be anticipated prior to imaging; scanner means for scanning said object placed in position; an image processing device for generating a tomographic image of said object from the projection data obtained by said scanner means; an extractor device for extracting said detection object selected in said selector device from within said tomographic image generated; and a display device for displaying said detection object extracted by said tomographic image and said extractor device.