According to the Mayo Clinic, the number of U.S. women undergoing mastectomies for breast cancer is rising again. Researchers say the number of surgeries declined in the 1990's, while the use of lumpectomies increased. But new imaging techniques--including MRI--are being used more frequently in the early stages of breast cancer, and experts say that because MRIs can spot cancer in more than one part of the breast, they may prompt doctors to advise a patient to have a full mastectomy.