Ultrasound (also called ultrasonography) is an imaging technique in which high-frequency sound waves are sent to a part of your body. Echoes from the ultrasound waves bouncing off the tissues of your body are displayed as images (called a sonogram) on a viewing screen.
The best way to understand what an ultrasound does is to first understand what it does not do. Ultrasounds are not a substitute for mammograms, nor are ultrasounds recognized as a general screening tool for cancer.
Instead, ultrasound is most often used in conjunction with other tests. For example, if a mammogram has turned up some sort of abnormality, or a if doctor has felt something unusual during a clinical exam, an ultrasound may be used to determine whether the abnormality is solid (such as either a benign fibroadenoma or a cancer) or fluid-filled (such as a benign cyst). An ultrasound cannot, however, determine whether a solid lump is cancerous, nor can it detect calcifications.
In addition, ultrasound of the breast is a common screening technique used in women under age 30. A young woman's breast tissue tends to be very dense and full of milk glands. On a mammogram, dense breast tissue looks white, which makes it almost impossible to see any cancerous growths, which also would be read as white. Many doctors say that trying to find a tumor in the midst of dense gland tissue in a mammogram can be like finding a polar bear in a snowstorm. Ultrasounds offer a better glimpse of young patients' breast tissue.
Also, ultrasounds commonly are used to guide biopsy needles to exact spots in the breast where anything suspicious has been located.