Breast Cancer Diagnosis
Magnetic Resonance Breast Imaging (MRI, MR)
Magnetic resonance breast imaging (MRI, MR) has been approved by the U.S. Food and Drug Administration (FDA) since 1991 for use as a supplemental tool, in addition to mammography, to help diagnose breast cancer. Breast MRI is an excellent problem-solving technology. It is often used to investigate breast concerns first detected with mammography, physical exam, or other imaging exams. MRI is also excellent at imaging the augmented breast, including both the breast implant itself and the breast tissue surrounding the implant (abnormalities or signs of breast cancer can sometimes be obscured by the implant on a mammogram). MRI is also useful for staging breast cancer, determining the most appropriate treatment, and for patient follow-up after breast cancer treatment.
In addition to its role as a diagnostic tool, researchers are investigating whether breast MRI may be useful in screening younger women at high risk of breast cancer. Most women under 40 years of age do not require any breast imaging. However, some of these younger women are at high risk of breast cancer, as determined by a strong family history or a mutated breast cancer gene (BRCA1 or BRCA2), and therefore need breast imaging before age 40. MRI may be helpful for these women because the technology is effective in dense breast tissue and most young women have dense breasts. However, mammography is currently the only FDA approved exam to be used to screen for breast cancer in women with no symptoms of the disease (such as a breast lump). Even if MRI one day gains approval as a breast cancer screening tool for women at high risk of the disease, it would most likely be used in conjunction with mammography on select women.
- How Breast MRI is Performed
- Benefits of an MRI Exam of the Breast
- Limitations to an MRI Exam of the Breast
- Summary of Breast MRI
Sagittal (side or lateral view) MRI of the breast with contrast enhancement showing chest and blood vessels.
Unlike mammography which uses low dose x-rays to image the breast, MRI uses powerful magnetic fields and radio waves to create images of the breast. The MRI system is able to switch magnetic fields and radio waves to achieve views in any plane and from any orientation while x-ray mammography requires re-orientation of the breast and mammography system for each view desired.
The main component of most MRI systems is a large tube-shaped or cylindrical magnet. To begin the MRI exam, the patient is positioned on a special table inside the MRI system opening where a magnetic field is created by the magnet. Each total MRI exam is typically comprised of a series of 2 to 6 sequences, with each sequence lasting between 2 and 15 minutes. An “MRI sequence” is an acquisition of data that yields a specific image orientation and a specific type of image appearance or “contrast.”
A recent advance in MRI breast imaging is the GE Breast Array Coil, which allows for bilateral breast imaging and improved differentiation between various breast tissue. The patient is placed directly on the table and the technologist has visual control of breast position through a transparent window.
During the examination, a radio signal is turned on and off, and subsequently, the energy which is absorbed by different atoms in the body is echoed or reflected back out of the body. These echoes are continuously measured by the MRI scanner. A digital computer reconstructs these echoes into images of the breast. The tapping heard during the MRI exam is created when “gradient coils” are switched on and off to measure the MRI signal reflecting back out of the patient’s body. A benefit of MRI is that it can easily acquire direct views of the breast in almost any orientation while mammography requires re-orientation of the breast and mammography system for each view desired. An MRI exam of the breasts typically takes between 15 and20 minutes. The most useful MRI technique for breast imaging uses a contrast material called Gadolinium DTPA, which is injected into a vein in the arm before or during the exam to improve the quality of the images. This contrast agent helps produce stronger and clearer images and “highlight” any abnormalities.
MRI has several potential benefits in helping to investigate breast concerns. An MRI exam allows breast images to be taken in any plane and from any orientation. One particular advantage of MRI is that it is highly sensitive to small abnormalities that can sometimes be missed with other exams. For instance, a mammogram or ultrasound (sonogram) of the breast may reveal breast cancer in one area. However, an MRI of the breast may show that the cancer is in fact multi-focal; small tumors are present in several areas of the breast. Determining the extent of breast cancer with MRI can help indicate treatment: breast conserving surgery (lumpectomy) or breast removal (mastectomy). Mastectomy is indicated if there are multiple tumors.
MRI is also useful in helping to determine whether breast cancer has spread into the chest wall. If there is evidence of breast cancer in the chest wall, a patient often needs to undergo chemotherapy before breast cancer surgery. Not knowing whether the chest wall is involved can delay chemotherapy and cause the patient to have both chemotherapy and radiation therapy after surgery. Physicians can also use MRI to detect cancer recurrences in women who have already been treated for breast cancer with lumpectomy. In addition, MRI can assess whether a newly inverted nipple is evidence of a retroareolar cancer, a tumor under the areola (the pigmented region surrounding the nipple).
Another major benefit of MRI is that it plays a significant role in the visualization of breast implants. MRI can often show if an implant is leaking or ruptured. MRI can also image the breast tissue that is compressed by an implant. Implants can obscure some of the breast tissue on conventional mammogram images, making abnormalities or sings of cancer more difficult to see. This is because the x-rays used for mammography cannot penetrate silicone or saline implants well enough to image the overlying or underlying breast tissue. MRI imaging does not have this limitation. However, mammography is still the best tool for evaluating breast tissue and for screening for breast cancer. There is currently no routine recommendation for using MRI as a cancer screening tool in women with implants, although it can be helpful in selected cases.
Because MRI is effective in women with dense breast tissue, researchers are investigating whether breast MRI would be an appropriate screening tool for young women at high risk of breast cancer. While most women under 40 years of age do not require any breast imaging (i.e., mammography), some younger women are at high risk of breast cancer due to a strong family history or a mutated breast cancer gene (BRCA1 or BRCA2). However, young women tend to have dense breast tissue, which can make screening mammography less effective. This is because breast tissue density shows up as a white region on a mammogram just as a cancer would. (As women age, their breasts become less dense, increasing the effectiveness of screening mammography). With MRI, physicians are able to more easily distinguish between density and breast abnormalities.
A number of studies have shown that MRI may be effective in screening women at high risk of breast cancer. In a study published in the July 18, 2001 issue of the Journal of the National Cancer Institute, researchers found that breast MRI was superior to screening mammography in detecting breast cancer in young women at high risk of the disease. MRI was able to find more breast cancers than mammography and was less likely to miss breast cancer.
|Benefits of Breast MRI|
MRI has significant promise as a supplemental tool to mammography in the diagnosis of breast cancer. However, MRI still has additional hurdles to undergo in order to gain wider acceptance and use. First, MRI cannot always distinguish between cancerous and non-cancerous abnormalities, which can lead to unnecessary breast biopsies. A biopsy of an MRI-detected abnormality can be particularly difficult, too, because physicians must learn how to use MRI to guide them to the abnormality. (MRI system researchers and manufacturers continue to develop new MRI systems and tools to allow MRI-guided breast biopsy). This is necessary because the abnormality found with MRI may not be visible with traditional image guidance, such as mammography or ultrasound.
Another drawback of breast MRI is that it is unable to image calcifications, tiny calcium deposits that can indicate breast cancer. Mammography, on the other hand, can reliably image calcifications, which are often associated with early-stage breast cancers such as ductal carcinoma in situ (DCIS). Also, MRI has been shown to produce a moderate amount of false-positive results. In other words, the results of an MRI sometimes show that a suspicious abnormality is present in the breast when, in fact, cancer is not present.
Furthermore, MRI is an expensive exam; an average MRI of the breast costs approximately $3000 versus $100 per screening mammogram. Patients need to lie still in a prone (face down) position during the exam to eliminate motion in the images. Though an MRI exam is not painful, patients must tolerate any claustrophobia (fear of small spaces) they may have. A contrast agent is also given prior to the exam to improve image quality. See the above section on How Breast MRI is Performed for more information on the contrast agent.
Finally, MRI is not widely available for breast imaging. Currently, breast MRI is performed mostly at research centers. Many community MRI centers do not perform breast MRI. New MRI systems specifically designed to image the breasts have been developed but are not widely available at this time.
|Limitations of Breast MRI|
To summarize, breast MRI is a very useful breast cancer diagnostic tool and is excellent at imaging the augmented breast. MRI can be used effectively to gain information about breast abnormalities detected with mammography, physical exam, or other breast imaging modalities. MRI is also useful in helping to stage breast cancer, evaluate treatment options, and follow-up after treatment has been completed.
While breast MRI is an effective problem-solving technology, it has limitations as a screening tool for breast cancer. Breast MRI’s limited availability, expense, and frequent non-specificity (failure to distinguish between cancerous and non-cancerous abnormalities) have slowed its widespread acceptance. However, if research continues to show that MRI can be effective as screening women at high risk of breast cancer (particularly young women who have dense breast tissue that makes it difficult to detect cancer with mammography), it may one day play a larger role in breast cancer detection.
The following chart summarizes the benefits and limitations of breast MRI:
|Benefits of Breast MRI||Limitations to Breast MRI|