From Pam Stephan,
Your Guide to Breast Cancer.
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About.com Health's Disease and Condition content is reviewed by V.K. Gadi, MD

Mammography and Breast MRIs (Magnetic Resonance Imaging) are diagnostic screening tests. These imaging systems are used for screening and detecting breast conditions including breast cancer. Neither of these non-invasive tests prevent or treat breast cancer. The greatest value of these tests is for early detection of breast cancer. This disease is most curable when it is caught early.

How are Mammograms and Breast MRIs different?

During a mammogram, X-rays penetrate your breast to record differences in the density of your breast tissue. To get different views of your breast, each breast will have to be repositioned and imaged twice. For the best image, compression will be used so that your breast tissue will remain motionless and will be thinner during the exposure. X-rays are known to cause DNA damage to cells, so the lowest possible dose will be used to take the image.

During an MRI, no radioactivity is used. Magnetic fields, radio waves, and a contrast agent will be used to take hundreds of cross-sectional images of both breasts at the same time. The injected contrast agent (usually gadolinium) increases the contrast between soft and hard tissue. The resulting image is 10 to 100 times higher contrast than a standard mammogram. When the test is complete, the gadolinium will be cleared from your system by your kidneys. There is no known long-term health risk from the magnetic fields and radio waves used during an MRI.

Why Don’t We All Have MRIs Instead of Mammograms?

Mammograms are widely available and relatively inexpensive ($100). Most health insurance and Medicare will help cover the cost of a mammogram. Mammography is useful for women at any risk level for breast cancer.

Breast MRIs are available primarily in urban and metropolitan areas and are more expensive than mammograms, costing from $1,000 to $2,000. The cost is not always covered by insurance and Medicare. Contrast agent must be injected, and a patient must lie still for 30 to 60 minutes inside a large tube during the exam. If the facility can't do image-guided biopsies, then you may have to redo the test at a radiology center that can combine an MRI with breast biopsy.

Who Should Have Breast MRIs?

Women who are at high risk for developing breast cancer should consult their doctors or oncologists about having a breast MRI. High risk includes women who have already had cancer in one breast or who carry the genetic mutations BRCA1 and BRCA2. It also includes those whose mother, sisters or daughters have had breast cancer and women who have mutated TP53 or PTEN genes, or who have had chest radiation treatments between ages 10 to 30 for diseases such as Hodgkin’s disease.

Here are some online risk assessment tools. The three different kinds of risk calculators will give you different results. Discuss your concerns about having a breast MRI with your doctor to determine whether or not the test would benefit you.