MRI: Magnetic Resonance Imaging

MRI is a powerful diagnostic tool that uses magnetic fields, not radiation, to create images of the body. The best MRI technique involves the use of a special "breast coil." During an MRI, you lie still and are moved in and out of a narrow tube as the machine creates images of your body. If you're claustrophobic, being confined within an MRI machine for up to an hour can be difficult. Some facilities have an open MRI machine to avoid this problem, or you may be given a mild sedative.

The value of MRI for breast cancer detection remains uncertain. Some doctors believe MRI can distinguish a breast cancer from normal breast gland tissue better than other techniques. But MRI is expensive and requires highly specialized equipment and highly trained experts. Relatively few MRI centers exist, especially outside of major cities. Even at its best, MRI produces many uncertain findings. Some radiologists call these "unidentified bright objects," or UBOs. MRI also cannot detect calcifications. Finally, MRI can dislodge certain metal devices, such as pacemakers, in some people.

It is unlikely that MRI will be used as a general screening tool for breast cancer. It may, however, prove useful in:

• evaluating a woman who has a palpable mass that isn't visible with ultrasound or mammography
• assessing a lesion in the densely glandular breast of a young woman
• screening a young woman who is at high risk for cancer because of a significant family history of breast cancer or an abnormal breast cancer gene

Additional advantages of MRI:

• MRI is sometimes used successfully in women who have breast cancer cells in an underarm lymph node, but have no breast mass that doctors are able to feel or see on a mammogram. In these cases, where mastectomy is typically recommended, MRI can help find the precise site of the cancer's origin within the breast. Finding the cancer's precise origin can expand a woman's treatment options from only mastectomy to include lumpectomy plus radiation.
• MRI can help determine if a cancer is limited to one area of the breast, or if it is "multicentric" and involves more than one area. Knowing this affects treatment choices, since mastectomy is necessary for multicentric disease. This is particularly useful for women with invasive lobular cancer, which has a tendency to be diffuse or multicentric.
• MRI is good for looking at scar tissue. It can evaluate a significant change in the lumpectomy site.
• MRI scanning can detect leakage from a silicone-filled breast implant, since it easily distinguishes silicone gel from surrounding normal breast and chest wall tissues.
• In the case of metastatic breast cancer, MRI can evaluate other parts of the body. A woman who has progressive back pain, or who develops new weakness or numbness in the arms or legs (not just hands or feet), can have an MRI scan of her back. The scan can help identify serious conditions such as the possible presence of a spinal tumor or brain metastasis.