If you agree to take part in this study, you will be asked to remove your clothes from the waist up and put on a gown. A female technologist will give you an injection of Tc-99m sestamibi in a vein in your arm. This is a drug routinely used for breast imaging. About 10 minutes after your injection, you will be asked to sit in a chair for about 40 minutes. The technologist will position your breast between two small cameras. The cameras will apply a very light compression to your breast to make sure there is no movement during the picture. We will take two pictures of each breast. Each picture takes 10 minutes. You will also be asked to fill out a short questionnaire. If you are found to have additional breast lesions, your doctor and radiologist will be notified so that additional imaging or biopsies can be performed.