OBJECTIVE. The purposes of this study were to evaluate the diagnostic performance of dedicated breast PET (dbPET) in cases of unexpected uptake and to define parameters associated with malignancy. MATERIALS AND METHODS. There are two types of high-resolution dbPET systems. One has two platelike detectors that compress the breast. This study was conducted with the other type, on which the patient lies prone and the breast hangs through a ring without compression. In total, 627 consecutively registered women underwent ¹⁸F-FDG PET/CT and dbPET for pretherapeutic or posttherapeutic evaluation of breast cancer, prior suspicion of breast cancer, or cancer screening. Areas of abnormal FDG uptake, excluding known breast cancers, were analyzed. Uptake was morphologically categorized as focus, mass, or non-mass. Quantitative values were obtained, including the maximum standardized uptake value (SUV_max), peak SUV (SUV_peak), total lesion glycolysis (TLG), metabolic tumor volume (MTV), and lesion-to-background ratio (LBR). Clinical parameters were also assessed. Parameters were compared between breast cancer and noncancer groups; multivariate logistic regression analysis was performed. RESULTS. Of 40 instances of abnormal uptake, 13 were breast cancer. Morphologic features differed between cancer and noncancer groups (p = 0.0122). Among the cancers, 76.9% (10/13) had mass, 15.4% (2/13) had nonmass, and 7.7% (1/13) had focus uptake. Of noncancerous findings, 3.7% (1/27) were mass, 40.7% (11/27) nonmass, and 55.6% (15/27) focus uptake. SUV_peak (p = 0.0234), TLG (p = 0.0017), MTV (p = 0.004), and LBR (p = 0.0432) also differed between groups. Results of multivariate analysis indicated that morphologic category at dbPET was independently associated with malignancy. CONCLUSION. Morphologic features of abnormal uptake at dbPET are associated with breast cancer and may be useful for diagnosing lesions of unknown histologic composition.

Dedicated breast positron emission tomography (dbPET) is a new diagnostic imaging modality recently used in clinical practice for the detection of breast cancer and the assessment of tumor biology. dbPET has higher spatial resolution than that of conventional whole body PET systems, allowing recognition of detailed morphological attributes of radiotracer accumulation within the breast. ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) accumulation in the breast may be due to benign or malignant entities, and recent studies suggest that morphology characterization of ¹⁸F-FDG uptake could aid in estimating the probability of malignancy. However, across the world, there are many descriptors of breast ¹⁸F-FDG uptake, limiting comparisons between studies. In this article, we propose a lexicon for breast radiotracer uptake to standardize description and reporting of image findings on dbPET, consisting of terms for image quality, radiotracer fibroglandular uptake, breast lesion uptake.

Background: Using phantoms and clinical studies in prone hanging breast imaging, we assessed the image quality of a commercially available dedicated breast PET (dbPET) at the detector’s edge, where mammary glands near the chest wall are located. These are compared to supine PET/CT breast images of the same clinical subjects. Methods: A breast phantom with four spheres (16-, 10-, 7.5-, and 5-mm diameter) was filled with ¹⁸F-fluorodeoxyglucose solution (sphere-to-background activity concentration ratio, 8:1). The spheres occupied five different positions from the top edge to the centre of the detector and were scanned for 5 min in each position. Reconstructed images were visually evaluated, and the contrast-to-noise ratio (CNR), contrast recovery coefficient (CRC) for all spheres, and coefficient of variation of the background (CV_B) were calculated. Subsequently, clinical images obtained with standard supine PET/CT and prone dbPET were retrospectively analysed. Tumour-to-background ratios (TBRs) between breast cancer near the chest wall (close to the detector’s edge; peripheral group) and at other locations (non-peripheral group) were compared. The TBR of each lesion was compared between dbPET and PET/CT. Results: Closer to the detector’s edge, the CNR and CRC of all spheres decreased while the CV_B increased in the phantom study. The disadvantages of this placement were visually confirmed. Regarding clinical images, TBR of dbPET was significantly higher than that of PET/CT in both the peripheral (12.38 ± 6.41 vs 6.73 ± 3.5, p = 0.0006) and non-peripheral (12.44 ± 5.94 vs 7.71 ± 7.1, p = 0.0183) groups. There was no significant difference in TBR of dbPET between the peripheral and non-peripheral groups. Conclusion: The phantom study revealed poorer image quality at < 2-cm distance from the detector’s edge than at other more central parts. In clinical studies, however, the visibility of breast lesions with dbPET was the same regardless of the lesion position, and it was higher than that in PET/CT. dbPET has a great potential for detecting breast lesions near the chest wall if they are at least 2 cm from the edge of the FOV, even in young women with small breasts.

Breast positron emission tomography (PET) has had insurance coverage when performed with conventional whole-body PET in Japan since 2013. Together with whole-body PET, accurate examination of breast cancer and diagnosis of metastatic disease are possible, and are expected to contribute significantly to its treatment planning. To facilitate a safer, smoother, and more appropriate examination, the Japanese Society of Nuclear Medicine published the first edition of practice guidelines for high-resolution breast PET in 2013. Subsequently, new types of breast PET have been developed and their clinical usefulness clarified. Therefore, the guidelines for breast PET were revised in 2019. This article updates readers as to what is new in the second edition. This edition supports two different types of breast PET depending on the placement of the detector: the opposite-type (positron emission mammography; PEM) and the ring-shaped type (dedicated breast PET; dbPET), providing an overview of these scanners and appropriate imaging methods, their clinical applications, and future prospects. The name “dedicated breast PET” from the first edition is widely used to refer to ring-shaped type breast PET. In this edition, “breast PET” has been defined as a term that refers to both opposite- and ring-shaped devices. Up-to-date breast PET practice guidelines would help provide useful information for evidence-based breast imaging.

Purpose: To evaluate the clinical feasibility of high-resolution dedicated breast positron emission tomography (dbPET) with real low-dose ¹⁸F-2-fluorodeoxy-d-glucose (¹⁸F-FDG) by comparing images acquired with full-dose FDG. Materials and methods: Nine women with no history of breast cancer and previously scanned by dbPET injected with a clinical ¹⁸F-FDG dose (3 MBq/kg) were enrolled. They were injected with 50% of the clinical ¹⁸F-FDG dose and scanned with dbPET for 10 min for each breast 60 and 90 min after injection. To investigate the effect of the scan start time and acquisition time on image quality, list-mode data were divided into 1, 3, 5, and 7 min (and 10 min with 50% FDG injected) from the start of acquisition and reconstructed. The reconstructed images were visually and quantitatively compared for contrast between mammary gland and fat (contrast) and for coefficient of variation (CV) in the mammary gland. Results: In visual evaluation, the contrast between the mammary gland and fat acquired at a 50% dose for 7 min was comparable and even better in smoothness than that in the images acquired at a 100% dose. No visual difference between the images with a 50% dose was found with scan start times 60 and 90 min after injection. Quantitative evaluation showed a slightly lower contrast in the image at 60 min after 50% dosing, with no difference between acquisition times. There was no difference in CV between conditions; however, smoothness decreased with shorter acquisition time in all conditions. Conclusions: The quality of dbPET images with a 50% FDG dose was high enough for clinical application. Although the optimal scan start time for improved lesion-to-background mammary gland contrast remained unknown in this study, it will be clarified in future studies of breast cancer patients.