Feasibility research is proposed for the development of computed ultrasonic reflection tomography for medical diagnostic imaging. The proposed method has the potential to provide quantitative images of breast cross sections displaying the ultrasonic reflectivity at a spatial resolution of approximately one wavelength. This resolving capability, coupled with the noninvasive character of ultrasonic interrogation, offers potential for the development of an innovative commercial instrument for breast imaging. The imaging technique may also have application to scientific research in the area of ultrasonic characterization of biological tissue. Specific aims of the study are designed to provide experimental evidence to test the theoretically predicted capability of reflection tomography as implemented using a large aperture source. Data simulation algorithms and image reconstruction methods will be developed to investigate the method under ideal conditions. An experimental, rotate-only fan-beam reflection tomographic scanner is proposed to examine the practical imaging characteristics. Imaging experiments using resolution test targets, tissue simulators and in vitro biological tissues will be examine the practically attainable spatial resolution, ease of implementation and overall feasibility of the method. This research is concerned with the development, initial testing and evaluation of ultrasonic diagnostic imaging system.