What is Dedicated Breast PET (Positron Emission Mammography, PEM)?

What is it?
Breast PET uses an injection of a short-lived radioactive sugar (¹⁸FDG) into the body to detect metabolically active lesions such as cancer. PET, or more often PET-CT, is commonly used to stage the whole body in patients with larger breast cancers or suspected recurrence. Newer technologies can provide detailed PET images of the breasts to assess local extent of breast cancer.

How it works
The radioactive sugar accumulates in cancer cells in the breast and emits high-energy positron radiation that is detected and analyzed. For one such system, the patient is seated and the breast is gently stabilized; positioning is otherwise like mammography (Fig. PET-1).

**Figure PET-1. Dedicated breast PET (PEM).** Imaging takes 10 minutes per view (total of 40 minutes for a standard 4-view examination) and usually starts at least one hour after injection of the radiotracer. Twelve “slice” images are reconstructed from each view (Figure 19). The patient must be fasting for 4-6 hours prior to the test and should rest quietly for about an hour after injection prior to imaging.

Imaging takes 10 minutes per view (total of 40 minutes for a standard 4-view examination) and usually starts at least one hour after injection of the radiotracer. Twelve “slice” images are reconstructed from each view (Fig. PET-2). The patient must be fasting for 4-6 hours prior to the test and should rest quietly for about an hour after injection prior to imaging.

**Figure PET-2. Digital Mammogram and breast PET images of ductal carcinoma in situ (DCIS).** Vague asymmetry (arrow, left image) is seen on the MLO mammogram (an image taken from a side angle) of this 48-year-old woman with heterogeneously dense breasts. Stereotactic biopsy showed DCIS (early breast cancer). Breast PET was performed one hour after i.v. injection of 10 mCi 18F-fluorodeoxyglucose (FDG), showing more extensive disease than was suspected on the mammogram with segmental uptake of the radiotracer on CC (middle) and MLO (right) breast PET 6-mm thick slice images (arrows).

Benefits
Breast PET is generally considered a diagnostic test used to determine the extent of cancer within the breasts, and can be used as an alternative to breast MRI for that purpose [1, 2]. In women with newly diagnosed breast cancer being treated with chemotherapy prior to surgery, breast PET can also help monitor response to treatment. In addition, breast PET may help distinguish recurrence of cancer from scar in women who have been previously treated for breast cancer. Uncommonly, it can be used for problem solving (Fig. PET-3). It is a relatively new modality and not widely available.

Considerations
Breast PET exposes the patient to a moderately high whole body radiation dose and is not used for screening [3]. The very back part of the breast near the chest wall and the axillary lymph nodes are better evaluated with MRI.

**Figure PET-3. Breast PET distinguishes cancer from silicone implant rupture.** Left MLO mammogram (left image, taken from the side of the breast) in this 65-year-old woman shows retroglandular silicone implant that has ruptured with extracapsular silicone obscuring most of the tissue. A larger mass is noted just above the implant (arrow). MLO breast PET (right), performed one hour after i.v. injection of 9 mCi 18F-fluorodeoxyglucose (FDG), shows intense uptake in irregular mass (arrow) as well as uptake in one axillary lymph node which has been included on the image (red arrow). Final pathology revealed a 5.5 cm invasive ductal carcinoma with 8 metastatic lymph nodes.

References

1. Berg WA, Madsen KS, Schilling K, et al. Breast cancer: Comparative effectiveness of positron emission mammography and MR imaging in presurgical planning for the ipsilateral breast. Radiology 2011; 258:59-72

2. Narayanan D, Berg WA. Use of breast-specific PET scanners and comparison with MR imaging. Magn Reson Imaging Clin N Am 2018; 26:265-272

3. Narayanan D, Berg WA. Dedicated breast gamma camera imaging and breast PET: Current status and future directions. PET Clin 2018; 13:363-381

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