Abstract: The presence of a mechanical disturbance, such as an ultrasonic field, within a body can alter an x-ray image of the body in a way that can enhance its diagnostic capabilities. In the first mode of operation of the invention an acoustic field causes displacement within the body through radiation forces detected by recording two x-ray images, one image with the sonic field on and a second image with the sonic field off. Each image is stored in a computer memory, and the images are digitally subtracted, pixel by pixel, to yield a differential image. In the second mode of operation of the invention, the sonic field is a standing or traveling acoustic wave within the body. An image is recorded with bursts of pulsed x-rays where the bursts are produced synchronously with the mechanical disturbance. The method makes the x-ray sensitive to differences in tissue sound speed or stiffness so that it acquires an additional contrast mechanism.