The overall objective of this project is the refinement of two-dimensional ultrasonic imaging of the heart by the simultaneous display of structures ad intracardiac blood flow patterns. In addition, the characteristics of tissue comprising the heart wall and valve leaflets will be determined and macrostructure of blood fow patterns such as jets and vortices will be delineated. The research covered by this progress report has involved the investgation of a 4-element transducer array in which two elements operate as senders while two function as receivers. Delay differences between transmit pulses and receiver range gates scan a point through a three-dimensional volume illuminated by broad beams. Off-line reconstruction is planned and a system is under construction. Synthetic aperture imaging is undergoing watertank studies and an adaptive ultrasonic gain control is under development. Signal processing programs have been implemented and include frequency displays for one- and two-dimensional images for filtration, differentiation, moving target indication, and Laplacian edge enhancement. Histograms of signal amplitude have facilitated logarithmic compression and reassignment of amplitude in bimodal distributions. Temporal fluctuations of amplitude and spectra can be readily displayed. Doppler studies have consisted of apparatus construction, modification of system electronics and software generation. Profiles of steady flow have been obtained in the experimental setting. New apparatus has been generated for computer-based tissue and flow macrostructure studies and model studies of gratings have been used to test the system and to identify the effects of beam nonuniformities and requirements for precise beam alignment. BIBLIOGRAPHIC REFERENCES: Waag, R. C., and Gramiak, R.: Characterization of tissue with ultrasound. Proc. of the Am College of Radiology Conf on Computerized Tomography in Radiology, St. Louis, Mo., April 1976 (in press). Gramiak, R. and Waag, R. C.: Ultrasonic cardiac motion image reconstruction. Proc. of the Am College of Radiology Conf on Computerized Tomography in Radiology, St. Lous, Mo., April 1976 (in press).