Ultrasound is a painless procedure that uses sound waves to make images of the inside of your body. The sound waves bounce off surfaces in your body, and the "echoes" are recorded and transformed into video or photographs.
It’s often used in addition to mammography to tell whether a lump in a breast is a cyst (a fluid-filled sac) or a solid mass, which might be cancer. Ultrasound can also help pinpoint the position of a tumor. This guides the doctor to the exact place to insert a needle during a biopsy.