Breast MRI

Breast MRI, short for magnetic resonance imaging, uses a strong magnetic field and radio waves — rather than X-rays — to produce highly detailed images of the breast. It is the most sensitive imaging test for breast tissue and is reserved for situations where this extra detail is valuable. Breast MRI is recommended as an addition to mammography for women at high risk of breast cancer, such as those who carry an inherited gene mutation. It is also used to measure the exact size and extent of a known cancer before treatment, to check how well a tumor is responding to chemotherapy given before surgery, to investigate findings that remain unclear after other tests, and to assess the condition of breast implants. A contrast agent is usually injected into a vein to make abnormal areas easier to see.

Because a contrast agent is typically used, kidney function may be checked beforehand, and any history of allergic reactions should be discussed. For women being screened, the test is often scheduled for a particular point in the menstrual cycle to give the clearest images. It is important to tell the staff about any metal implants, pacemakers, or other devices in the body, as well as about pregnancy or breastfeeding, since these can affect whether and how the test is performed. All metal objects and jewelry must be removed before entering the scanner.

During a breast MRI, the person lies face down on a padded table with the breasts positioned within a specialized cushioned opening. The table then slides into a large tube-shaped scanner. The machine makes loud knocking and humming sounds while it works, and ear protection is provided. It is important to stay as still as possible so the images remain sharp. The contrast agent is given through a small tube in a vein partway through the test.

Breast MRI does not use radiation and is considered safe. Reactions to the contrast agent are uncommon and usually mild. Some people find the enclosed space uncomfortable, and a mild sedative can be arranged for those who experience claustrophobia. Because the test is so sensitive, it can detect harmless areas that lead to additional imaging or biopsy, so it is used selectively rather than for routine screening of average-risk women.

The radiologist describes the findings using the BI-RADS system. If an area of concern is identified, a targeted ultrasound — sometimes called a second-look ultrasound — or an MRI-guided biopsy may be arranged to examine it further. The results are combined with those from mammography and ultrasound to give a complete picture.