Ultrasound is an imaging technique that sends high-frequency sound waves through your breast tissues and converts them into images 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 doctor has felt something unusual during an exam, an ultrasound may be used to determine whether the abnormality is solid (such as either 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.
Ultrasound also is used frequently in women under age 30. A younger woman's breast tissue tends to be very dense and full of milk glands. On a mammogram, this tissue looks white, which makes it almost impossible to see any cancerous growths, which would also 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.
Ultrasounds also are frequently used to guide biopsy needles to exact spots in the breast where anything suspicious has been located.