Ultrasound is an imaging test that sends high-frequency sound waves through your breast and converts them into images on a viewing screen. It is not used on its own as a screening test for breast cancer. Rather, our staff at the Women's Imaging Center uses it to complement and guide other tests. If an abnormality is seen on a mammogram or detected through a physical exam, ultrasound is the best way to find out if the abnormality is solid (such as benign fibroadenoma or cancer) or fluid-filled (such as a benign cyst). It cannot determine whether a solid lump is cancerous.