Use of Breast-Specific PET Scanners and Comparison with MR Imaging

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Key points

  • Positron emission mammography shows sensitivity similar to MR imaging in detecting malignant breast lesions with better specificity than MR imaging.

  • Breast PET can be used in women in whom breast MR imaging is contraindicated.

  • Breast imagers should interpret breast PET to assure full correlation with prior breast imaging, history, and appropriate management in conjunction with a multidisciplinary specialty team.

Breast-specific PET devices

Whole-body PET (WBPET) and PET-CT are not optimal for evaluation of the breasts due to supine positioning and low resolution (5–6 mm), which limit detection of subcentimeter cancers.3 Breast PET uses detectors positioned close to the breasts either similar to mammography with gentle stabilization or in the prone or semiprone position. PET requires coincidence detection of the pair of 511 KeV gamma rays emitted in opposite directions at the time of annihilation of the positron. This requirement

Imaging protocol and radiation exposure

In clinical studies using breast-specific PET systems, patients are injected with approximately 185 to 370 MBq (5–10 mCi) FDG after fasting for 4 to 6 hours. Blood glucose is tested prior to injection and should be in the normal range. Patients must rest quietly for 60 to 90 minutes following injection prior to commencing imaging. For PEM systems, typically both craniocaudal and mediolateral oblique views are obtained for 5 to 10 minutes of scan time per breast per view. For other systems, the

Local extent of disease

There is a lack of consensus about the use of preoperative MR imaging to assess local extent and select patients for breast-conserving treatment.13 A large prospective multicenter trial of PEM and MR imaging in 388 women with newly diagnosed biopsy-proven cancer, where breast-conserving therapy was planned, was led and reported by Berg and colleagues.1 Of 388 index breasts with cancer, 75 (19%) ultimately were pure ductal carcinoma in situ (DCIS). For the 386 index malignancies that had

Axilla

Often it is difficult to include the axillae with breast-specific PET because of positioning similar to mammography or even on a prone table. In the prospective multicenter trial described,1 the false-positive and false-negative rates for axillary nodal metastases were high for both PEM and MR imaging. Of 19 axillae suspicious on PEM, only 10 (53%) actually had nodal metastatic disease; of 27 axillae suspicious on MR imaging, only 13 (48%) had metastatic nodes. Of 326 axillae negative on PEM,

Quantification

Using WBPET, quantitative, and for PEM, semiquantitative uptake of FDG have been shown to correlate with known histopathologic and immunohistochemical prognostic factors including risk of nodal metastases; greater uptake predicts response to chemotherapy.25, 26 Increasing uptake has been shown with increasing tumor grade and with triple receptor-negative tumor type.15, 25 Lower uptake has been observed in invasive lobular carcinoma.15 Like the standardized uptake value (SUV) used in whole-body

Background 18F-2-deoxy-2-fluoro-d-glucose uptake and breast density

Uptake of FDG in normal breast tissue increases with visual mammographic BI-RADS breast density and decreases with patient age/postmenopausal status. An early retrospective study of 94 women with suspicious breast lesions29 looking at a region of interest in the normal contralateral breast showed average mean (and maximum) background glandular PUV of 0.33(0.60) in fatty breasts, 0.41(0.72) in breasts with scattered fibroglandular density, 0.65(1.05) in heterogeneously dense breasts, and

Response to primary chemotherapy

Noritake and colleagues32 compared the performance of PEM with that of WBPET in assessing the therapeutic response to neoadjuvant chemotherapy in 20 patients. Patients were imaged at 3 time points: before, during (interim), and after neoadjuvant chemotherapy. PEM PUVmax was highly correlated with SUVmax on WBPET (Pearson correlation coefficient r = 0.78). At the interim time point, when therapy could be changed based on imaging findings, reduction in PUVmax did not distinguish patients who

Other applications

Although 1 study of 265 women, including 165 who were asymptomatic, used PEM to screen for breast cancer,33 this will not be discussed further due to the substantial whole-body radiation exposure and patient preparation that render breast PET impractical for screening. In 1 study34 evaluating PEM in women with suspicious calcifications going to biopsy, among 40 patients with 15 malignancies, PEM identified 14 (93.3%) cancers with 1 false-negative intermediate-grade DCIS and 1 false-positive

Summary

Breast-specific PET imaging demonstrates high sensitivity for breast cancer and has shown promise for evaluating extent of disease in patients diagnosed with breast cancer. Although PEM and MR imaging are complementary, and the use of both improves overall performance, it is not recommended to use both because of the substantial cost and minimal added benefit in such an approach. Breast MR imaging is widely used in breast imaging clinics. Although the lack of specificity is a known disadvantage

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    Disclosures: The authors have nothing to disclose.

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