Abstract: We propose a new ultrasound image formation method, which we call shear-wave reciprocity imaging (SRI), to produce images based on the sound speed and attenuation of tissue. These acoustic properties carry important diagnostic information but are not revealed in conventional B-mode images except as artifacts. For example, in breast imaging the “posterior features” (shadowing/enhancement) BiRADS descriptor depends on these properties. In contrast to conventional B-mode imaging that produces speckle images of variations in tissue acoustic impedance, we propose SRI as a method for speckle-free imaging of an attenuation/sound speed parameter. SRI images are complementary to both B-mode and elastography images yet are produced using the same backscatter imaging geometry as conventional ultrasound. SRI relies on the principle of mechanical reciprocity to measure local variations in acoustic radiation force, which relate to attenuation and sound speed. While using acoustic radiation force impulses similar to ARFI imaging, SRI is designed to be insensitive to elastic properties and to specifically image the attenuation/sound speed parameter. The aims of this project are to implement SRI on a linear-array imaging system, characterize its sensitivity and resolution through in vivo measurements prior to biopsy, and validate SRI in ex vivo breast tissue from mastectomy. We expect that the additional information provided by SRI will ultimately improve lesion categorization and reduce the number of biopsies required by replacing qualitative estimates of lesion attenuation from B-mode shadowing with parametric acoustic images.