The objectives of the proposed research are to develop techniques and instrumentation to form very high resolution ultrasonic images and to investigate their clinical utility in breast imaging. We hypothesize that clinical breast images with resolution up to ten times finer than that of commercially available scanners can be formed using advanced phased array techniques developed in our laboratory including: 1) adaptive imaging to maintain image resolution and sensitivity when imaging through aberrating media such as subcutaneous arrays. We further hypothesize that such systems will improve the clinical utility of breast ultrasound in lesion detection and classification, microcalcification detection, and needle-guided biopsies. The primary goals of this research are the characterization of tissue- induced ultrasonic image degradation, the development of improved algorithms for adaptive and harmonic imaging, and the construction and clinical evaluation of a real-time adaptive and adaptive/harmonic imaging system for breast imaging.