Breast MRI: How and Why it is Used

Mammography is a highly effective surveillance tool for detecting early breast cancer and is still the only imaging method that is proven to decrease deaths from breast cancer. However, some women need additional screening, so breast MRI is a useful adjunct to mammography.

During a breast MRI, a powerful magnet is used to obtain hundreds of images of the breasts, before and after intravenous injection of dye material. A breast MRI takes approximately 30-45 minutes, during which time patients are asked to remain almost completely motionless in order for the test to be as accurate as possible. Fortunately, no radiation is required to take the images.

The advantage of breast MRI – and sometimes its disadvantage – is that it is extremely sensitive, which means that it can detect both cancerous and non-cancerous (benign) lesions. However, some cancers and benign tumors can appear similar on breast MRI and, as a result, breast MRI can sometimes lead to unnecessary biopsies – and anxiety –  for patients.

Dr. Jose Net, director of breast imaging services at Sylvester Comprehensive Cancer Center, says that women may have misconceptions about the appropriate use of breast MRI.

“Some people believe that breast MRI is a better test, that it can find all cancer, or that it can replace mammography,” he says. “Breast imagers are often in a dilemma when recommending MRI, because we know its limitations of having high false positive rates and relatively poor sensitivity. But, because it has very low misses on actual cancers and a good ability to identify small cancers, we are very much in favor of using this technology appropriately.”

Patients at high risk for breast cancer may benefit from screening with breast MRI, along with a mammogram, says Dr. Net. High risk patients may include:

  • Known BRCA 1 and 2 mutation carriers, or their untested 1st degree relatives
  • Strong family history of breast cancer
  • Known history of genetic cancer syndromes
  • A history of mantle radiation, an older form of radiation, prior to the age of 30
  • Lifetime risk assessment greater than 20 percent

MRI has a good record of sensitivity in detecting breast malignancy for patients at elevated risk, but that high-sensitivity comes with a high false-positive rate, leading to the potential need for follow-ups, or even biopsies.

The test is also not recommended as a stand-alone screening because it may miss some cancers that a mammogram would find, such as cancers associated with calcifications, which show up on mammography.

Often used in women who have already been diagnosed with breast cancer, breast MRI can help measure the size of the cancer and look for other tumors in the same or other breast. Doctors often use the MRI to track a patient’s response to chemotherapy treatment.

This test is FDA recommended, and remains the gold standard in evaluating silicone breast implants for possible rupture.

Unfortunately …

Some women with claustrophobia or noise sensitivity may have problems with the noise of the magnets or the confined space and having to lie perfectly still for long periods of time.

While gadolinium in the contrast dye enhances the quality of the MRI images, a recent finding showed that it may deposit in soft tissue, including the brain. No harmful effects have been documented.

Some metal implants may cause a problem. If you have any of the following, your care team may rule out a MRI:

  • An implanted defibrillator or pacemaker
  • Clips used on a brain aneurysm
  • A cochlear (ear) implant
  • Metal coils inside blood vessels

“Breast MRI is an important tool for breast cancer screening in women who meet very specific criteria,” says Dr. Net, “and breast imagers are the most informed specialists to help your doctor determine if breast MRI is right for you.”


 Mary Jo Blackwood, RN, MPH, is a contributing writer for UMiami Health News. She is a two-time breast cancer thriver, and a long-time freelance medical writer based in St. Louis, MO and Hartsel, CO. She has written physician-to-physician magazine articles, consumer health articles, and webpages for cancer patients, among other things.