Magnetic Resonance Imaging (MRI)

A breast MRI is a high-resolution way of visualizing the breast without radiation. It is useful when a doctor suspects there is a tumor that is not showing up during a physical exam or mammography. It may also be used to determine the size and extent of a known tumor.

Breast MRI can be used in addition to mammography or ultrasound. Doctors use MRI when they suspect the presence of an "occult" breast cancer. This is when a woman has a swollen underarm lymph node that is found, by aspiration or biopsy, to contain cancer cells, yet no sign of cancer appears on a breast exam and mammogram. In most such patients, breast MRI can identify the site of the cancer if that particular cancer originated from the breast. MRI can also be used to examine the chest wall or pectoral muscles for suspected cancer, as these areas are hard to reach with mammography.

Another feature of breast MRI is its ability to detect hidden second cancers in the breast of a woman who has already been diagnosed with one cancer. In some cases, the detection of a second cancer in the same breast may alter treatment approaches in selecting lumpectomy and radiation therapy (in the case of a single breast cancer) versus mastectomy (if more than one cancer is found in the breast).

A potential downside to using breast MRI is its ability to detect lesions that are not cancerous, but are suspicious enough to require a surgical biopsy procedure. Additional roles of breast MRI that are under evaluation include its use in detecting cancers in the opposite breast of a patient with one breast cancer already diagnosed.

Doctors also use breast MRI to determine the size and extent of a known tumor in a breast cancer patient. This is especially useful if the cancer is difficult to measure by mammography, as can be the case with an infiltrating lobular cancer. If you are taking anticancer drugs to shrink a tumor before surgery (a process called neoadjuvant therapy) MRI can help reveal whether the tumor is responding to the medication. In addition, MRI may be used to check for recurrences after lumpectomy.

Breast MRI requires special equipment designed specifically for breasts. To have an MRI, you lie very still within a large machine, face down, with your breasts suspended into a cushioned, bra-like holder. Your face and head are near the open ends of the magnet chamber. During the procedure, a dye is injected into your arm. Short bursts of high-frequency waves stimulate hydrogen atoms in cells to emit signals that are collected and turned into an image by a computer. The image is made in 5-10 sequences, each of which is 3-5 minutes long, with breaks in between. The entire examination takes about 45 minutes.

Next >> Breast Ductogram

In This Article:
Detecting Breast Cancer
Breast Self-Exam and Clinical Exam
Mammography
Breast Ultrasound
Magnetic Resonance Imaging (MRI)
Breast Ductogram
Breast Biopsy

From the Harvard Health Publications Special Health Report, Breast Cancer: Strategies for Living. Copyright 2004 by the President and Fellows of Harvard College. Illustrations by Harriet Greenfield, M.A., and Jesse Tarantino. All rights reserved. Used with permission of StayWell. Harvard Medical School does not endorse products.
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