A breast MRI is a study that uses a magnetic field to generate images of your breast before and after a contrast injection. If MRI is used, it should be in addition to, not instead of, a mammogram. While an MRI is likely to detect most cancers, it may miss some cancers that could be detected with a mammogram.
According to the American Cancer Society Guidelines, women at high risk — about 20 percent or greater lifetime risk based on family history or history of prior chest wall treatment with radiation — should get an MRI and a mammogram beginning at age 30. Women at moderately increased risk — 15 percent to 20 percent lifetime risk — should talk with their doctors about the benefits and limitations of adding MRI to their yearly mammogram.
Yearly MRI screening is not recommended for women whose lifetime risk of breast cancer is less than 15 percent.
Women at high risk include those who:
- Have a known BRCA1 or BRCA2 gene mutation
- Have a first-degree relative — mother, father, brother, sister or child — with a BRCA1 or BRCA2 gene mutation and have not had genetic testing themselves
- Have a lifetime risk of breast cancer of 20 percent to 25 percent or greater, according to risk-assessment tools based mainly on a family history from both the mother and father’s sides
- Had radiation therapy to the chest when they were between the ages of 10 and 30 years
- Have a genetic disease such as Li-Fraumeni syndrome, Cowden syndrome or Bannayan-Riley-Ruvalcaba syndrome, or have first-degree relatives with one of these syndromes
Women at moderately increased risk include those who:
- Have a lifetime risk of breast cancer of 15 percent to 20 percent according to risk-assessment tools based on family history
- Have a personal history of breast cancer, ductal carcinoma in situ, lobular carcinoma in situ, atypical ductal hyperplasia or atypical lobular hyperplasia
- Have extremely dense breasts or unevenly dense breasts when viewed by mammograms
Several risk-assessment tools, including BRCAPRO, the Claus model and the Tyrer-Cuzick model, are used to estimate a woman’s breast cancer risk. Based on different combinations of risk factors, these tools approximate estimates of breast cancer risk. Depending on the tool used, different risk estimates may be calculated for the same woman.
Preparing for a Breast MRI
To prepare for an MRI study of your breasts:
- Remove all metallic objects, such as watches, eyeglasses, chains and rings. Let the technologist know if you have any metal in your body, particularly pacemakers, breast expanders, metallic coils in your brain or metal fragments. For more information, see the MRI Safety Checklist [PDF].
- Do not bring any credit cards into the room as the magnet can erase all relevant information.
- Although you are given a gown, you may want to wear a comfortable two-piece outfit since you will be asked to remove all clothing above the waist.
- Let the technologist know if you are or could be pregnant.
About the Procedure
During the MRI, you will be asked to lie on your stomach while your breasts are positioned in a holder called the “breast coil.” Since you will be lying on your stomach, when you look up you will be able to see outside the MRI tube. You will be given a call button to press should you need to speak to us during the procedure. Most patients are able to tolerate the study.
One of the nurses will test your renal function and start an IV that will be used to give you intravenous contrast. The contrast used is called gadolinium; it does not contain iodine and is different from the type of contrast used for CAT scans. Allergic reactions are rare.
Images are taken of both breasts before and after the contrast is given. It is important that you remain as still as possible during the procedure, especially after the contrast material is given, so that the images captured are clear.
When interpreting MRI studies, we look at morphology — similar to what we do on a mammogram and ultrasound — including the shape, margins, effect on surrounding tissue and size of possible abnormalities.
We also evaluate kinetics, or the blood flow into potential lesions. Normal breast tissue takes up the contrast gradually over the first 10 minutes after the contrast is given. Breast cancers usually show what is called “rapid wash in and wash out” of contrast, meaning that most cancers take up the contrast avidly within the first two minutes after the injection and give it up quickly. This is thought to be related to abnormal blood vessels in tumors.
MRI-guided biopsy may be indicated if the abnormality seen on MRI is not visible on your mammogram or ultrasound; this requires a second MRI at least 24 hours after the first study is done.