http://www.cancer.org/cancer/breastcancer/moreinformation/breastcancerearlydetection/breast-cancer-early-detection-breast-ultrasound
Breast ultrasound
Ultrasound, also known as sonography, is an imaging method that uses sound waves to look inside a part of the body. In the most common version of this test, a small, microphone-like instrument called a transducer is placed on the skin (which is first lubricated with ultrasound gel). It emits sound waves and picks up the echoes as they bounce off body tissues. The echoes are converted into an image on a computer screen. This test is painless and does not expose you to radiation.
Breast ultrasound is often used to evaluate breast problems that are found during a mammogram or on physical exam. Ultrasound helps distinguish normal findings like cysts or fat lobules from suspicious breast changes that need biopsy. In someone with a suspicious breast mass, ultrasound can be used to look for enlarged lymph nodes under the arm. Breast ultrasound is often used to guide a needle to biopsy breast lesions and abnormal lymph nodes.
Ultrasound is sometimes used along with mammograms to screen certain women, such as those with dense breast tissue as seen on a mammogram. Some studies have shown that having a yearly screening ultrasound in addition to a mammogram will show more invasive cancers than mammograms alone in women with dense breasts. But ultrasound also shows many findings that may lead to follow-up or needle biopsy but turn out not to be cancer.
A yearly mammogram after age 40 is recommended to screen for breast cancer in all women regardless of breast tissue type. The use of ultrasound instead of mammograms for breast cancer screening is not recommended.
Women at high risk are recommended to have screening done yearly with a mammogram and an MRI. If MRI screening is done, ultrasound screening is not needed. Talk with your doctor to see if your mammograms show that you have dense breast tissue and, if so, ask what additional tests may be right for you.