This application is for the continuation of research and development of reflex transmission imaging (RTI), a method for producing orthographic images of tissue attenuation using augmented B-scan technology. Unlike other methods for producing orthographic transmission images, which usually require water immersion, RT images can be made with a single B- scan-size transducer. Conventional B-scan and RTI are totally compatible. RTI provides supplementary information to the diagnostician- -a second viewing perspective and sensitivity to tissue attenuation. RTI should find application in the evaluation of many medical conditions. During the preceding grant period we have established the feasibility of this method, made major improvements to it, completed one instrument that is now ready for clinical evaluation and begun conversion to RTI of a second instrument. Our laboratory experimens demonstrated the potential of RTI for imaging kidney stones. We have now licensed RTI for use with lithotripsy only. During the proposed continuation we will conduct additional basic studies to improve the effectiveness and expand the applicability of RTI. These studies will include optimization of the method we have developed for reducing the effects of backscatterer inhomogeneity on the image. We will develop improved methods of image display and, using cadaver organs, investigate the applicability of RTI to a wider range of organs and pathologies. We will complete, in two stages, the conversion to RTI of a new Diasonics SPA-400 annular array imaging system. This system was given to SRI for use on this grant by SRI's lithotripsy licensee, without commercial obligation beyond lithotripsy applications. Using this instrument, the diagnostic applications of RTI will be explored at the University of California Medical School. A peripheral-organ RTI system, recently completed under this grant, will be clinically evaluated at the Palo Alto Medical Foundation clinic, with special emphasis on its potential application to the breast. We will develop a second generation RTI system that produces real-time RT images (the current instruments require 1 to 15 seconds to make an RT image, although their B-scans are realtime). This will involve two- dimensional transducer array technology and parallel processing.