Because there are differences in the orientation of internal tissues of the breast as prepared for x-ray mammography (compression, standing mode) and as prepared for ultrasound imaging (uncompressed, supine), correlation of image data between these two modes is not precise. This project attempts to improve detection and diagnosis of breast masses in dense breast tissue by developing an ultrasound imaging system that correlates with x-ray mammography. The approach is (1) develop compression paddles which allow transmission of ultrasound without undue attenuation or multiple reflections and (2) to ultrasonically scan the breast while it is held by ultrasound transmission compression paddles which provide the same pressure and breast orientations that are used in x-ray mammography. Two experimental ultrasound imaging systems based on this approach have been developed at IBC. One unit is designed to demonstrate the effectiveness of an instrument which combines x-ray and ultrasound. The other unit, which does not include x-ray, is designed for patients for whom x-ray mammography is inappropriate. These prototypes, which have many advantages over the hand-held transducer methods currently used for breast ultrasound, will undergo further development, and clinical studies will. be carried out with the goal of obtaining data that will encourage the development of commercial instruments based on these new concepts.