Background: Breast MRI has excellent sensitivity, but is very expensive and suffers from low specificity. Additional benign biopsies are prompted by MRI in 24-40% of patients. Molecular Breast Imaging (MBI) is a new nuclear medicine technique developed at Mayo. Preliminary MBI results indicate a sensitivity of ~88% for the detection of tumors < 10 mm. The cost of an MBI procedure is expected to be a factor of 5 less than an MRI examination.