Specific Aim 3: To compare the pretreatment MRI with post treatment MRI (as a secondary surrogate endpoint to breast cancer risk reduction). We hypothesize that tumor response can be measured by contrast washout characteristic in patients with preinvasive and very early breast cancer treated with aromatase inhibitor. Consistent with this, we have previously demonstrated that patients with advanced breast cancer show a reduction in vascularity in response to chemotherapy. Further, there is a trend for a more profound suppression in those achieving a pathological response on lumpectomy/mastectomy specimen.