Ultrasound uses reflected sound waves to produce an image of organs and other structures in the body. This technology can be useful in helping doctors pinpoint the location of tissue for testing or treatment. For example, ultrasound can be used to help guide the placement of a needle or other instrument during a biopsy. A biopsy is a procedure to collect a sample of tissue collected from an organ or other part of the body. The tissue is then examined for abnormalities, such as cancer, by a doctor trained to look at tissue samples (pathologist).

Gel or oil may be used to help transmit the sound waves. A small handheld instrument called a transducer is passed back and forth over the area of the body being examined. The transducer sends out high-pitched sound waves (above the range of human hearing) that are reflected back to the transducer. A computer analyzes the reflected sound waves and converts them into a picture. From this picture, the doctor can identify the location of tissue for biopsy and can use the ultrasound image to guide the needle into the selected tissue for sampling. The needle itself may have a special tip that is very reflective under ultrasound, so that it shows up well in the image.