Ultrasonic imaging exploits phase contrast: One way to ultrasonically image objects with negligible acoustic absorption is to use an optical microscopy technique

Soft tissues in the human body that are almost invisible to X-rays can often be imaged by ultrasonic techniques. When an ultrasonic wave enters the human body, it may pass through many different kinds of tissue, each with somewhat different acoustic properties, At each tissue interface, such as the boundary between a heart valve and the surrounding blood, some of the incident sound will be reflected and may be detected for use in forming an ultrasonic image. Ultrasound is now being used routinely by medical practitioners to measure the motion and condition of heart valves, to check on the growth of fetuses, to detect changes in the brain, and in numerous other applications.