Unlike a mammogram, which uses X-rays to create images of the breast, a breast MRI uses magnets and radio waves to produce detailed 3-dimensional images of the breast tissue. Before the test, you may need to have a contrast solution (dye) injected into your arm through an intravenous line. Because the dye can affect the kidneys, your doctor may perform kidney function tests before giving you the contrast solution. The solution will help any potentially cancerous breast tissue show up more clearly. Some people experience temporary discomfort during the infusion of the contrast solution.
Cancers need to increase their blood supply in order to grow. On a breast MRI, the contrast tends to become more concentrated in areas of cancer growth, showing up as white areas on an otherwise dark background. This helps the radiologist determine which areas could possibly be cancerous. More tests may be needed after breast MRI to confirm whether or not any suspicious areas are actually cancer.
For more information on breast MRI please visit http://www.radiologyinfo.org/en/info.cfm?pg=breastmr