Breast MRI, or magnetic resonance imaging, works by using very strong magnetic fields to line up and detect the hydrogen atoms in your body, information which is then used to construct a detailed image of your body structure. For women with higher risk of breast cancer, yearly breast MRI's are usually recommended in addition to breast mammograms, due to their greater degree of accuracy. MRI's can also be performed to double-check if a mammogram reading is accurate. MRI's can not only detect whether there are unusual areas of breast tissue, but can also see if lymph nodes (small bean-shaped tissues that remove cell waste, germs, and other harmful substances from the body) are enlarged, usually a sign of cancer. During an MRI, the patient must stay completely still inside a large machine that completely surrounds the patient, otherwise the MRI will have to be performed again. The entire procedure takes around 30 minutes. The test does not cause any pain.