Ultrasound uses high frequency sound waves to image the breast and is used to better characterize lumps found by you or your doctor, or to provide further information about findings on a mammogram. Ultrasound is not used for routine breast cancer screening because it does not consistently detect certain early signs of cancer such as microcalcifications (tiny deposits of calcium in the breast that cannot be felt but can be seen on a conventional mammogram). A cluster of microcalcifications may indicate that cancer is present. Ultrasound imaging of the breast is used to distinguish between solid tumors and fluid-filled cysts. Ultrasound can also be used to evaluate lumps that are hard to see on a mammogram, or findings that are suspicious on Breast MRI.