BASICS OF BREAST IMAGING
Screening imaging (Screening Mammograms)—Screening imaging consists of series of x-ray tests of the breast (traditionally 2 mammogram views per breast) that are used to look for evidence of a breast cancer in women who are not having any symptoms of breast cancer.
Diagnostic imaging—Diagnostic imaging consists of a series of additional imaging tests that are done to better evaluate a specific problem that has been identified in a woman’s breast, such as:
A palpable lump
Bloody nipple discharge
A focal, persistent area of pain
An abnormality seen on screening imaging
These tests typically include additional mammogram views, ultrasound, and/or MRI. They are performed to help the radiologist identify the problem and determine whether or not a biopsy is necessary. They are done at the discretion of the doctor ordering the test and/or the radiologist.
BI-RADS® classification—Every time a woman gets an imaging test of the breast, the radiologist will score it according to what is known as the BI-RADS® classification system. This is a way for the radiologist and other physicians to communicate about what they are seeing on the imaging and whether or not additional workup or biopsy is necessary.
BIRADS classifications range from 0 to 6:
BI-RADS® 0—Inconclusive (needs additional imaging)
BI-RADS® 2—Benign finding(s) (such as a known cyst)
BI-RADS® 3—Probably benign (additional imaging in 6 months)
BI-RADS® 4—Suspicious abnormality (biopsy should be considered)
BI-RADS® 5—Highly suggestive of malignancy (biopsy needed)
BI-RADS® 6—Biopsy-proven malignancy
Breast density—Breast tissue density described on mammograms refers to the glandular tissue of the breast. The glandular tissue is maintained by the hormones produced by the ovaries as a part of menstrual cycles. Generally, younger women who have functional ovaries will have denser breast tissue than postmenopausal women. That said, there is a lot of variability from one woman to the next. Forty to forty-five percent of all women will be described as having dense breast tissue on mammogram. Denser breast tissue makes it more difficult for the radiologist to see abnormalities on mammogram. In addition, some newer studies suggest that women who have dense breast tissue may be at a slightly higher risk for developing breast cancer in the future.
Digital mammograms—A digital mammogram is a two-dimensional x-ray used to detect abnormalities in the breasts. Using these two views, the radiologists are able to “reconstruct” a three-dimensional view of the breast. Overall, mammograms are quite accurate in detecting breast cancers. They will identify 78% of breast cancers present. This test is, however, significantly limited by how dense a woman’s breast tissue is. The greater the density of the breast tissue, the more difficult it is for the radiologist to accurately interpret the mammogram and rule out the existence of a breast cancer.
Digital tomosynthesis—This newer technology has been developed to minimize some of the limitations of traditional two-dimensional mammograms. It combines the traditional two views of a regular mammogram with a second camera that sweeps in a 15-degree arc (similar to the panoramic x-rays done at the dentist) to “look around the corner,” giving the radiologist a 3-dimensional view of the breast. Studies show that this technique is more accurate in differentiating dense breast tissue from breast cancers. It has resulted in a 30% reduction in the number of women who need to return for additional mammograms and ultrasounds to determine what the radiologists are seeing. This test is also one that can be used as an adjunct to 2-dimensional mammograms for women with dense breast tissue.
Breast ultrasound—Breast ultrasound is an imaging test that uses sound waves to look for abnormalities in the breast. Because it uses sound waves, there is no radiation exposure. Traditionally, this test has been used in cases where a woman and/or her physician has felt a lump in the breast or when an abnormality seen on mammogram could be a mass. Therefore, this has been traditionally used as a diagnostic test and not a screening test.
Screening breast ultrasound—Recently, as we have begun to explore the significance of breast density, there has been an increased interest in looking at ultrasound as a screening tool for the entire breast. Several techniques have been developed. In one, an ultrasound technician or a radiologist scans each breast in its entirety. However, it is dependent on the experience and technique of the person performing the test. It also is limited by the size of the breast and the volume and depth of tissue that has to be evaluated. More recently automated machines have been developed, providing more uniformity of the test throughout various locations where it is utilized. However, these automated ultrasound exams also results in large volumes of images that must be reviewed and can take a significant period of time to interpret.
Screening breast ultrasound has been suggested as an adjunct to mammography in women with dense breast tissue. Studies have shown that using this technique has the capability of detecting more abnormalities and cancers. This detection, in turn, increases the number of biopsies performed. However, upon biopsy many of these abnormalities are found to be benign (non-cancerous). And of the cancers detected by screening breast ultrasound alone, it is not known whether these cancers would have developed into something of significance or had a bearing on the patient’s outcome or life expectancy.
Breast MRI—Breast MRI is a sophisticated test that utilizes a combination of magnets and intravenous dye to find evidence of breast abnormalities. It looks for anatomic abnormalities (masses) and blood flow abnormalities that have been shown to be characteristic of breast cancers. The pros and cons of this test are as follows:
Pros—Studies show that breast MRI is more accurate than mammography at detecting invasive breast cancers and aggressive forms of noninvasive breast cancer (with 91%–93% accuracy). It has been shown to be a good screening tool for women in high-risk groups (BRCA mutations carriers, very strong family history of breast and ovarian cancer, women with a history of mantle radiation, and women with a calculated lifetime risk of developing breast cancer at 20%–25% or more). MRI should not replace the use of mammography in these women. The recommended screening pattern should incorporate mammography and MRI, each once per year, spaced 6 months apart.
Cons—Studies show that breast MRI is not as good as mammography for detecting atypical lesions or lesser aggressive noninvasive breast cancers. It is also known for false positives (detecting lesions that are not breast cancers but must be biopsied to prove that). It is a much more expensive test, often costing thousands of dollars. Finally, it is also involves the use of an intravenous Gadolinium dye.