It directs very high frequency sound waves through the skin into the body and measures the reflected waves. The waves are pitched so high that they cannot be heard. Because sound waves travel at different speeds in different tissues, an echo is produced as different tissue levels are traversed. These echoes are then recorded to make the image. A sonogram is a highly valuable method for determining whether a mass found in the breast is a cyst or a mass.
Cysts are almost never due to cancer.
Masses that are not cysts are called solid and may be due to cancer. A sonogram is an accepted method of evaluating a known mass in this diagnostic use. Sonography has been proposed as a method of screening women for breast cancer, potentially useful in younger women and in all women with radiodense breasts. Although studies have been performed, it has not been proven sufficiently to support its use as a screening method for breast cancer.