Difference Between A Mammogram and A Breast MRI

How They Work and Understanding When One is Needed Over Another

Breast MRI
Color-enhanced slide shows magnetic resonance image (MRI) of individual breast.. Dr. Steven Harmes. Baylor University Medical Center, Dallas Texas

Early detection is key in surviving breast cancer and tests, like mammograms and breast MRIs, help detect breast cancers before they can be felt. 

That being said, it can be confusing understanding how these breast detection tests work, and why one is sometimes recommended over another. 

Let's compare mammograms and breast MRIs so you feel better prepared when or if you get one.

How are Mammograms and Breast MRIs different?

During a mammogram, X-rays penetrate your breast to record differences in the density of your breast tissue.

To get different views of your breast, each breast will have to be repositioned and imaged twice. For the best image, compression will be used so that your breast tissue will remain motionless and will be thinner during the exposure. X-rays are known to cause DNA damage to cells, so the lowest possible dose will be used to take the image.

During an MRI, no radioactivity is used. Magnetic fields, radio waves, and a contrast agent will be used to take hundreds of cross-sectional images of both breasts at the same time. The injected contrast agent (usually gadolinium) increases the contrast between soft and hard tissue. The resulting image is 10 to 100 times higher contrast than a standard mammogram. When the test is complete, the gadolinium will be cleared from your system by your kidneys. There is no known long-term health risk from the magnetic fields and radio waves used during an MRI.

The Good and The Bad

In terms of comparing the pluses and minuses of each test, breast MRIs are more expensive than mammograms.

They are also slower, usually taking 30 to 60 minutes, whereas a mammogram takes about 10 minutes. In addition, with a breast MRI, a woman may experience some claustrophobia.

Finally, even though breast MRIs may be better at finding certain cancers than mammograms, they are also more likely to find things that turn out not to be cancer — this is called a false positive.

This is why MRIs are reserved for women at high risk of developing breast cancer. 

Who Should Have Mammograms?

A woman of average risk for breast cancer can begin getting annual mammograms at the age of 40, according to the American Cancer Society.

Some women, at high risk for breast cancer, should also get a breast MRI in addition to their yearly mammogram — and may need to start at an earlier age, like around 30, depending on their doctor's advice.

Who Should Have Breast MRIs?

Women who are at high risk for developing breast cancer should consult their doctors or oncologists about having a breast MRI, in addition to a mammogram. High risk includes those who:

  • have the genetic mutations BRCA1 and BRCA2
  • have a first-degree relative with BRCA1 and BRCA2 gene mutation, but have not been tested themselves
  • Had radiation to the breast between the ages of 10 and 30
  • Have a genetic syndrome that predisposes to breast cancer 
  • Have a first-degree relative with one of the above syndromes
  • Have a lifetime risk of breast cancer of 20 to 25 percent, based on risk assessment tools used by a doctor

    Some women who have a personal history of breast cancer or breast conditions that carry a high risk for developing breast cancer in the future, like atypical ductal hyperplasia, may also need an MRI. Also, women with dense breasts on a mammogram may need a breast MRI. 

    In addition, breast MRIs are sometimes used to look more closely at suspicious areas on a person's mammogram, or to get a better look at the breast in someone who has already been diagnosed with breast cancer. 

    What Should I Do?

    Speak with your personal physician about when you should start breast cancer screening and whether you are average or high risk, Share any concerns you have about your mammogram and/or breast MRI with your doctor.
     

    Sources

    American Cancer Society. (2015). Breast Cancer Prevention and Early Detection: American Cancer Society recommendations for early breast cancer detection in women without breast symptoms. Retrieved October 20th 2015. 

    American Cancer Society. (2015). Mammograms and Other Breast Imaging Tests. Retrieved October 19th 2015. 

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