An ultrasound is usually performed when an abnormality has been found during mammography or physical examination. The test determines whether the abnormal area is solid tissue or a cyst filled with fluid. An ultrasound is more than 95 percent accurate in locating and correctly identifying the makeup of a lump.

This procedure uses high frequency sound waves to show the internal structures of the breasts on a monitor. The technologist moves a transducer, a microphone-like instrument, over the breast tissue, bouncing sound waves back to a sensor within the instrument. Unlike mammograms, these pictures enable the physician to observe the breast structure in motion. Ultrasound is also an instrument used to help guide aspirations and biopsies.