An image diagnostic system controls a probe to perform radial scanning within a body cavity and to acquire reflected signals through the probe. The system produces data based on the signals, constructs and outputs tomographic images of the body cavity and biotissue surrounding the body cavity. The system includes an extraction unit for extracting portions of the produced data on the basis of a frame rate upon successively outputting the tomographic images, and a first output control unit for forming, based on the extracted data, real time tomographic images of the body cavity and biotissue which are outputted in real time during radial scanning. A storage device stores the produced data, and a second output control unit forms, subsequent to the radial scanning, tomographic images of the body cavity and biotissue based on the stored data which are then outputted.
