Click here to view ultrasound images of breast conditions.

Breast ultrasound, also known as sonography or ultrasonography, is frequently used to evaluate breast abnormalities that are found with screening or diagnostic mammography or during a physician performed clinical breast exam. Ultrasound allows significant freedom in obtaining images of the breast from almost any orientation. Ultrasound is excellent at imaging cysts: round, fluid-filled, pockets inside the breast. Additionally, ultrasound can often quickly determine if a suspicious area is in fact a cyst (always non-cancerous) or an increased density of solid tissue (dense mass) which may require a biopsy to determine if it is malignant (cancerous).

The technologist holds the ultrasound transducer against the skin while imaging the breast. Image courtesy of http://www.SiemensMedical.com.

Though breast ultrasound has excellent contrast resolution, it lacks the detail (spatial resolution) of conventional mammography, and therefore, ultrasound is not approved by the U.S. Food and Drug Administration (FDA) as a screening tool for breast cancer. Rather, ultrasound is used to investigate an abnormality detected by mammography or during a physician performed breast exam. Currently, only mammography is FDA approved to look for breast cancer in asymptomatic women (women with no signs or symptoms of breast cancer).

What Can Ultrasound Show?

Physicians use ultrasound to evaluate breast abnormalities that have been found with screening or diagnostic mammography or during a clinical breast exam. Ultrasound may help detect some breast masses and is the best way to determine whether a cyst is present without placing a needle into the area of concern to aspirate fluid. Ultrasound is also useful in helping physicians guide a biopsy (tissue sampling) to determine whether a breast abnormality is cancerous. Physicians use ultrasound during core and fine needle aspiration biopsies (FNA) to determine where to place the needle. Ultrasound may also be used to prove whether a suspicious area is a lymph node. Lymph nodes have fatty centers which are often apparent on ultrasound images.

Ultrasound Versus Mammography

Ultrasound has excellent contrast resolution. This means, for example, that an area of fluid (cyst) and an area of normal breast tissue are easy to differentiate on an ultrasound image. However, ultrasound does not have good spatial resolution like mammography, and therefore cannot provide as much detail as a mammogram image. Ultrasound is also unable to image microcalcifications, tiny calcium deposits that are often the first indication of breast cancer. Mammography, on the other hand, is excellent at imaging calcifications. Ultrasound may be able to detect macrocalcifications (larger calcium deposits) in some cases.

Though most true breast lumps will be found by mammography or ultrasound, some abnormalities escape detection on both imaging tests. For example, a lump may be able to be felt but does not appear on mammography or ultrasound images. If this is the case, then fine needle aspiration biopsy (FNA) is often performed. Less than 30% of all breast biopsies are cancerous. In cases where the abnormality is not apparent on mammogram or ultrasound, the chances of cancer are significantly less.

Limitations of Ultrasound

Ultrasound may have a difficult time imaging a breast abnormality that can be felt due to:

• The deep location of the abnormality within the breast
• Operator and equipment factors
• The ultrasound image contrast between the abnormality and the surrounding breast tissue

Ultrasound is not FDA approved as a screening tool for breast cancer for a number of reasons. As stated above, ultrasound cannot reliably detect calcifications, tiny calcium deposits associated with many breast cancers. Ultrasound is also very operator-dependent. That is, the results of an ultrasound exam reflect the ultrasound technologist or the radiologist’s ability to properly manage the equipment. In addition, ultrasound cannot document how much breast tissue has been imaged; therefore, it is difficult to evaluate the thoroughness of the exam. Ultrasound also produces false positive or false negative results from time to time. This means that the ultrasound exam may indicate a breast abnormality when no abnormality is present, or conversely, ultrasound may miss an abnormality. Ultrasound is most valuable when used after mammogram or physical breast exams have indicated an abnormality.

How is Ultrasound Performed?

Breast ultrasound uses high-frequency waves to image to the breast. High-frequency waves are transmitted from a transducer through the breast. The sound waves echo off the breast; this echo is picked up by the transducer and then translated by a computer into an image that is displayed on a computer monitor.

The ultrasound unit contains a control panel, a display screen, and a tranducer (resembling a microphone or computer mouse). Before the exam begins, the patient will be instructed to lie on a special table. The ultrasound technologist will cover the part of the breast that will be imaged with a gel. The gel will lubricate the skin and help with the transmission of the sound waves.

Panoramic ultrasound of the breast showing proliferative breast disease and the lateral predominance of multiple cysts (dark regions on left side of image). Click here to view additional ultrasound images of breast conditions.

When the exam begins, the operator (either the ultrasound technologist or radiologist) will glide the transducer over the breast. The transducer will emit sound waves and pick up the echoes. The computer will then analyze the echoes and display an image on the computer screen. The shape and intensity of the echoes will depend on the density of the breast tissue. If a fluid-filled cyst is being imaged, most of the sound waves will pass through the cyst and emit faint echoes. However, if a solid tumor is being imaged, the sound waves will bounce off the tumor, and the pattern of echoes will be translated by the computer into an image that the radiologist will recognize as indicating a solid mass. Patients may feel a slight pressure from the transducer, but they will not hear the high-frequency sounds.

An ultrasound exam usually lasts between 20 and 30 minutes but may take longer if the operator has a difficult time finding the breast abnormalities being examined. Ultrasound does not use any radiation and is usually pain-free. An ultrasound exam costs much less than a CAT scan or MRI scan. 

Additional Resources and References

• The American Cancer Society provides information on breast ultrasound at http://www.cancer.org/
• To learn more about radiologists and other medical professionals involved in breast cancer diagnosis and treatment, please visit http://www.imaginis.com/breast+health/bc_treat_team.asp
• Click here to view additional ultrasound images of breast conditions.

 Updated: May 4, 2008

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