Inclusion Criteria:

1. Women who are 25 years of age or older
2. Newly diagnosed core-biopsy proven breast cancer
3. Has current mammography of all study breasts (within prior 3 months), including magnification views of suspicious calcifications (if any)
4. Recent clinical breast examination (within prior 3 months)
5. Has had full diagnostic workup with breast ultrasound (within prior 3 months) as indicated by mammographic and/or clinical findings
6. Has had percutaneous biopsy of all relevant suspicious findings on mammography, clinical examination, and ultrasound
7. After full diagnostic workup, participant is likely to be a candidate for breast conserving surgery.

8. No contraindications to breast MRI:

   • No pacemaker, aneurysm clip, or other implanted magnetic or ferromagnetic device;
   • No claustrophobia that cannot be controlled by medication with valium, ativan, or other sedative under her physician's orders;
   • Has intravenous access;
   • Weight < 300 lbs;
   • Physically able to tolerate positioning in the MRI scanner.
9. Agrees to undergo follow-up MRI or PEM at 6 months and/or MRI-guided vacuum-assisted biopsy, US-guided core biopsy, or PEM-guided biopsy if needed based on results of the MRI or PEM examination
10. Has signed study-specific consent form
11. Subject agrees to undergo a contrast-enhanced MRI and PEM scan within five business days of each other, prior to surgery.

Exclusion Criteria:

1. Male
2. Pregnancy
3. Active lactation or discontinued breastfeeding < 2 months prior
4. Age less than 25 years
5. Inability to provide informed consent
6. Prior radiation treatment to the affected breast(s)
7. Participant is scheduled for sentinel node procedure using radioactive Tc-99m within 24 hours after the scheduled PEM Flex study
8. Women planning prophylactic mastectomy without histologic confirmation
9. Individuals who are electing to undergo neoadjuvant chemotherapy prior to surgery (Note: Patients with prior contralateral breast cancer receiving chemoprevention with Tamoxifen, Arimidex, or other aromatase inhibitor are eligible)
10. Individuals who have had surgery on the study breast(s) within the past 12 months
11. Breast implant(s) in any study breast(s)
12. Women who have had distant metastatic disease either currently or in the past
13. Individuals with Type I or poorly controlled Type II diabetes mellitus
14. Individuals with a blood glucose level that is above 140 mg/dl at the time of PEM imaging
15. Has not had contrast-enhanced breast MRI or PEM within the past 12 months prior to study enrollment
16. Subject is currently enrolled in another breast imaging research study