High-frequency sound waves. Ultrasound waves can be bounced off of tissues using special devices. The echoes are then converted into a picture called a sonogram. Ultrasound imaging, referred to as ultrasonography, allows physicians and patients to get an inside view of soft tissues and body cavities, without using invasive techniques. Ultrasound is often used to examine the breast if a lump is felt, or if a density is seen on screening mammography. It is usually very good at telling the difference between a simple cyst, filled with fluid, and a solid mass of tissue. In addition, one can often tell the difference between benign tissue, such as a fibroadenoma, and a cancerous tissue, based on the ultrasound image.
Ultrasound is often used to help the doctor do a biopsy, as it allows a biopsy needle to be placed precisely in the lump.