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 have been 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, the American Cancer Society recently recommended that women at very high risk of developing breast cancer have annual breast MRI exams in addition to annual mammograms to increase the likelihood that breast cancer will be detected early, when the chances of survival are greatest. Because MRI is more sensitive than mammography, it can help detect cancer that may be missed by mammography. However, because this increased sensitivity can also lead to false positive results, which requires breast biopsy procedures, the American Cancer Society does not recommend MRI for all women.

MRI image of the breast, showing a lesion. Image courtesy of Siemens Medical.

Main Menu:

• How Breast MRI is Performed
• Benefits of an MRI Exam
• Limitations to an MRI Exam
• Summary of Breast MRI
• Breast MRI Case Studies

How Breast MRI is Performed

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 CP 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. Images courtesy of Siemens Medical.

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 30 and 60 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.

Transverse high-resolution MRI scan of breast and implants. Note the implant twisting on the upper (left) image and the implant valve on the lower (left) image.

Benefits of an MRI Exam of the Breast

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. Researchers are currently investigating whether MRI would be helpful to routinely use on breast cancer patients to screen for cancer in the opposite 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 may also be 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 sometimes 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.

Transverse fast acquisition breast MRI images at same level without contrast (upper) and with contrast (lower). Note how the abnormality in the lower breast image on the right is "highlighted" by the contrast (Gadolinium DTPA).

Because MRI is very sensitive, the American Cancer Society recently recommended that women at very high risk of developing breast cancer have annual breast MRI exams in addition to annual mammograms to increase the likelihood that breast cancer will be detected early. 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 may be able to more easily distinguish between density and breast abnormalities.

The American Cancer Society recommends breast MRI exams for women with one of the following:

• a BRCA1 (breast cancer gene 1) or BRCA2 (breast cancer gene 2) mutation
• a first-degree relative (parent, sibling, child) with a BRCA1 or BRCA2 mutation, even if they have yet to be tested themselves --a lifetime risk of breast cancer oft 20%-25% or greater, based on one of several accepted risk assessment tools that consider family history and other factors -a history of radiation to the chest between the ages of 10 and 30
• Li-Fraumeni syndrome, Cowden syndrome, or Bannayan-Riley-Ruvalcaba syndrome, or may have one of these syndromes based on a history in a first-degree relative

 Click Here to View Breast MRI Case Studies.

Limitations to an MRI Exam of the Breast

While MRI has significant promise as a supplemental tool to mammography in the diagnosis of breast cancer, there are limitations associated with MRI. First, MRI cannot always distinguish between cancerous and non-cancerous abnormalities, which can lead to unnecessary breast biopsies. Another drawback of breast MRI is that has historically been unable to effectively image calcifications, tiny calcium deposits that can indicate breast cancer. However, MRI technology is improving in this area. Still, mammography can reliably image calcifications, which are often associated with early-stage breast cancers such as ductal carcinoma in situ (DCIS).

Another drawback of breast MRI is that has historically been 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).

MRI image showing DCIS. Image courtesy of Siemens Medical.

Another potential drawback of MRI is that it 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. To some degree, all medical tests tend to lose some of their value when used in populations where the disease is not common.

Furthermore, MRI is an expensive exam; an average MRI of the breast costs approximately $1000 versus $100 per screening mammogram. MRI can also take longer than mammography: more than 30 minutes in addition to the administration of the contrast versus 10 to 15 minutes for a 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 nearly as widely available as mammography. However, access is increasing, and breast MRI is the second fastest growing MR procedure in the United States. In 2004, 24% of all facilities offering MR services offered breast MRI. According the Advisory Board, by 2010, an estimated 860,000 breast MR procedures will be performed.

Summary

To summarize, when used in conjunction with mammography, breast MRI can be a very useful breast cancer diagnostic tool. In particular, MRI as been shown to effectively image the augmented breast. MRI can be used effectively to gain information about breast abnormalities detected with mammography, physical exam, or other breast imaging modalities. Because of the increased sensitivity of MRI, the American Cancer Society recently recommended that young women at very high risk of the disease receive annual MRI exams in addition to annual mammograms. MRI may also useful for women diagnosed with breast cancer to detect cancer in the opposite breast, evaluate treatment options, and follow-up after treatment has been completed.

While breast MRI is an effective in some cases, it has limitations that prevent physicians from using it as a widespread screening tool for breast cancer. Its increased cost over mammography and frequent inability to distinguish between cancerous and non-cancerous abnormalities are drawbacks. However, the American Cancer Society's recent endorsement of MRI as a screening tool in young women at very high risk of breast cancer shows that the technology is beginning to play a more significant role in breast cancer detection.

The following chart summarizes the benefits and limitations of breast MRI:

 Click Here to View Breast MRI Case Studies.

 Click here for General Information on MRI.

Updated: May 4, 2008