Many of the technologies that have been developed for underwater acoustics are now being used to help diagnose health problems. The idea of sending sound waves into the ocean and recording what was reflected back arose during wartime as a way to detect submarines and other submerged objects. As advances were made in this technology, scientists thought there was potential for using sonar to detect objects in the human body.

Ultrasound uses sound to image the body. Just like sonar systems, it uses a transducer to send a sound signal into the body. The sound is transformed by whatever it comes in contact with. The reflected signal is processed and made into an image that looks like a picture. Very strong reflectors such as bone often appear as white structures. Poor reflectors, such as fluids that allow sound to pass through them, appear black. A fetus in utero will appear as a white image floating in black amniotic fluids.

The Navy developed special sonars and processing techniques to detect underwater mines. It is difficult to detect small objects in a constrained environment. This is especially true in shallow waters where the surface of the water and the bottom of the ocean are relatively close together. The sound waves reflect off the surface and the seafloor so it is hard to find objects that are somewhere in between. In addition, sound waves behave differently when bouncing off rocky bottoms, sandy bottoms, and when they encounter fish and other biological organisms in the water column. Navy scientists developed a complex signal processing technique to analyze sonar data for underwater mine detection.

Unmanned underwater vehicle using sonar to search for mines. Illustration courtesy of Naval Undersea Warfare Center Division Newport

Sailors looking for mines in a cluttered underwater environment face challenges that are similar to those of technicians looking for small calcifications in a mammogram of dense breast tissue. Signal processing experts thought that the techniques developed for mine detection had potential for enhancing medical images for breast cancer detection. By working with breast cancer radiologists, the Navy has successfully transferred their signal processing technology to the medical community. This technique is used for the enhancement of digital mammography. As a result, subtle information such as early stage cancers can be detected and visually enhanced to provide physicians with better information in the screening and diagnosis of disease.

Digital image enhancement of mammograms. The image on the left is a digitally enhanced close-up of the square box on the mammogram. Photos courtesy of Naval Undersea Warfare Center Division Newport

Additional Resources
• ONR - Technology Transfer