Evaluation of the Effect of Fasting and Exercise on Uptake of Tc-99m Sestamibi in Breast Tissue

Inclusion criteria: Arm 1: 1. Able to fast overnight or for 6 hours 2. Non-diabetic 3. Age \> 40 years 4. Negative pregnancy test, postmenopausal, or surgically sterilized 5. Negative mammogram at Mayo Clinic within the last 15 months (defined as screening mammogram or subsequent diagnostic workup with BI-RADS 1 or 2 final assessment) 6.No current breast concerns Arm 2: 1. Able to fast overnight or for 6 hours 2. Able to perform light to moderate exercise on an exercise bike 3. Non-diabetic and Body Mass Index \< 25 4. Age \> 40 years and \< 70 years 5. Negative pregnancy test, postmenopausal, or surgically sterilized 6. Negative mammogram at Mayo Clinic within the last 15 months (defined as screening mammogram or subsequent diagnostic workup with BI-RADS 1 or 2 final assessment) 7. No current breast concerns 8. No history of coronary artery disease, angina, stroke or peripheral arterial disease. Arm 3: 1. Able to fast overnight or for 6 hours 2. Willing to consume a dose of caffeine (200 mg), equivalent to that of an 8 oz Starbuck brewed coffee. 3\. Non-diabetic 4. Age \> 40 years 5. Negative pregnancy test, postmenopausal, or surgically sterilized 6. Negative mammogram at Mayo Clinic within the last 15 months (defined as screening mammogram or subsequent diagnostic workup with BI-RADS 1 or 2 final assessment) 7. No current breast concerns Arm 4: 1. Able to fast overnight or for 6 hours 2. Non-diabetic 3. Age \> 40 years 4. Negative pregnancy test, postmenopausal, or surgically sterilized 5. Negative mammogram at Mayo Clinic within the last 15 months (defined as screening mammogram or subsequent diagnostic workup with BI-RADS 1 or 2 final assessment) 6. No current breast concerns Exclusion Criteria: * Pregnancy test (if necessary) is not negative, or the patient is unable to complete the pregnancy test * Physically unable to sit upright and still remain still during two consecutive MBI studies over the course of a 2 hour period. * Have undergone unilateral or bilateral mastectomy * Breast implants or silicone injections * Are unable to understand and sign the consent form * Arm 2-also includes: Unable to perform light to moderate exercise for 12 minutes on a treadmill or a stationary bicycle * Arm 3: Unwilling to consume a 200 mg dose of caffeine