Magnetic-resonance imaging (MRI) is a way to scan the body without X-rays. The scan can be especially effective in detecting smaller breast cancer tumors and cancer that has spread into ducts. MRIs can detect 79% to 98% of cancerous lesions, making it the most accurate diagnostic tool for the disease. The machines are costly, however, so the scan is not as widely available as mammography. That's why experts recommend regular MRIs only for women at high risk for developing breast cancer. For patients who have already been diagnosed and treated with surgery, MRIs help reduce recurrence and improve survival rates; studies show that when an MRI is added to the yearly mammogram, breast cancer patients can detect cancer that has spread from one breast to the other early enough for successful treatment.