MRIs offer great detail, but they're expensive and usually used for high-risk women.

MRIs offer great detail, but they're expensive and usually used for high-risk women.(JENNIFER HULSHIZER/CORBIS)Magnetic resonance imaging (MRI) creates detailed images of your breast using a computer and powerful magnets. The procedure is used to follow up on worrisome symptoms or an inconclusive mammogram or ultrasound—though not always, because MRI is so expensive. MRI offers a very detailed picture of breast tissue, but it can also turn up a lot of false positives—suspicious results that prove, later, not to be cancer. High-risk women (with BRCA-1 or BRCA-2 gene mutations and/or a strong family breast cancer history) are often encouraged to get MRIs.

The procedure
MRIs are conducted with your body stretched out on a flat surface inside a metal tube. "You lie facedown and let your breasts hang through these huge holes," recalls Kim Heier, 42, of Simi Valley, Calif. The hollows in the table contain coils for picking up the MRI's magnetic signal. You may be given an injection of a dye that makes the mass in your breast easier to see.

More breast tests

Once the machine gets going, the buzzing, clicking, and thumping noises and the tight space can be nerve-wracking for some. Earplugs or headphones may be offered, and for people who are claustrophobic, taking a sedative drug beforehand might be an option.

On the other hand, some people find it appealing that there's nothing to do but wait. "Being the mother of three children, I don't get to sit down much, so lying in this machine for 30 minutes was kind of a relief," recalls Heier. "[Occasionally, they] reminded me not to move and I was thinking, 'No problem, I'm half asleep.'"

If you have cancer already
If you've been diagnosed with breast cancer in one breast, don't be surprised if your doctor suggests an MRI for your other breast. A 2007 study by the American College of Radiology Imaging Network found that for women who'd been diagnosed with cancer in one breast, MRI scans picked up more than 90% of cancers in the opposite (aka contralateral) breast that had been missed by mammography and a clinical breast exam at initial diagnosis.