Magnetic Resonance Imaging for the Diagnosis of Breast Cancer

Magnetic resonance imaging (MRI) has become well established as a valuable diagnostic tool since its use began almost 20 years ago. Its ability to see the body's soft tissues, even those surrounded by bone, has made it indispensable for imaging everything from the brain to the knee. In the last few years, researchers and physicians have begun to discover the benefits of MRI for imaging the breasts as well.

Mammography, the standard imaging technique for breast cancer screening, uses x-rays to see the structure of the breast. In contrast, MRI uses radio waves and a magnetic field, enabling physicians to get a very detailed look at the different soft tissues of the breast--and sparing patients exposure to the radiation used to produce x-ray images.

Currently, says Dr. David Bluemke, Clinical Director of MRI at the Johns Hopkins School of Medicine, MRI is used "as a secondary test, when the mammogram is not answering the question or when there are other, more complex questions that need to be answered." One group that benefits from MRI is women with a genetic predisposition for breast cancer. These women have a high risk for developing breast cancer at a younger age than the general population. Younger women tend to have denser breast tissue, which makes tumors harder to see using mammography but does not affect the quality of images obtained by MRI.

MRI is also useful for women who have had breast surgery or implants. In these cases, mammography may not be able to identify a tumor because of surgical scars or tissue distortion. Finally, MRI may be used for women who have had multiple suspicious lesions on mammography and have undergone multiple biopsies that turned out to be negative. For these women, MRI can often help identify problem areas or help a physician determine whether or not there is a need for further biopsies.

Several centers across the US and Europe are taking part in a 4½-year-long study to determine how well MRI characterizes and detects breast cancers. The study participants are women who have had an abnormality on mammogram and will undergo biopsy of the suspicious mass. "Only about one in five abnormalities seen on a mammogram is actually cancer," says Bluemke. Before the biopsy, researchers are using MRI in an attempt to determine, by identifying characteristics of malignant breast tumors, which abnormalities need to be biopsied. The hope is that, at some point in the future, use of MRI will help many patients avoid unnecessary biopsies.

In about one-third of the participants in this trial who have been found to have breast cancer, MRI has shown a larger area of cancer than what was anticipated by mammography. If the tumor mass is significantly larger than originally thought, this knowledge can have a tremendous impact on treatment. "Some of the conservative surgeries for breast cancer may not be appropriate, because you may not take out enough of the tumor," says Bluemke. In a small percentage of the study population--generally women who have a family history of breast cancer--a second tumor has been found where none was seen on mammography.

Currently midway through the study period, researchers have already discovered that some malignant tumors have a distinct appearance on MRI, which is termed "spiculated": they have a lot of projections off the edges of the tumor mass. "There are several other signs of cancer that are going to be found from this trial that should help generalize these techniques so that more people can institute them," says Bluemke.

So what's it like to have a breast MRI? First, an intravenous line is placed in the patient's arm vein. The IV is used to inject a contrast agent into the patient's blood during the procedure. "The contrast agent for MRI is extremely safe, and it's a very small amount," says Bluemke. Next, the patient changes into a hospital gown and lies on a flat table. The patient must lie on her stomach during the painless test, which generally takes about 20 minutes. The machine makes knocking sounds, but Dr. Bluemke says patients are generally provided with headphones so they can listen to music during the procedure. Several images are taken without the contrast agent. After about 10 minutes, the agent is injected via the IV line, and more images are collected. After some computer processing, three-dimensional images of the breasts are obtained and interpreted.

While MRI is a valuable addition to the physician's arsenal of diagnostic tests for breast cancer, Dr. Bluemke doesn't see a time when MRI will replace tried-and-true mammography. "For one thing, MRI is very expensive compared with mammography--probably 10 to 15 times more expensive. And mammography has the advantage of showing calcifications (calcium deposits). A lot of tumors are associated with calcifications."

Dr. Bluemke encourages all women to participate in this MRI trial and other trials that seek to understand breast cancer and improve its treatment. "Women can help themselves quite frequently by participating. And they're contributing to the general health of other women as well. Almost everyone knows someone with a family history of breast cancer."