Characterizing Primary Breast Cancer and Nodal Involvement with High-Resolution PET/MRI: Novel PET Configurations and Preliminary Results

High-resolution PET imaging has considerable potential to improve management of breast cancer, especially if it could be acquired simultaneously with the clinical standard of breast MRI. In this multimodal approach, PET contributes critical information on specific molecular subtypes and heterogeneity, while avoiding the challenge of reproducibly positioning the breast which confronts technologists when PET and MRI images are acquired separately. Using a compact, high-resolution and MR-compatible PET system (VersaPET) mounted into a breast MRI table, we have begun to assess the feasibility of this approach by collecting preliminary FDG data on primary tumors in breast cancer patients. In order to augment this approach to examine nodal involvement, we also performed a simulation study that incorporates novel detector geometries to expand the FOV to include axillary lymph nodes which are critical for diagnosing metastasis. We evaluated scanner geometries with limited angle sampling and features including time of flight (TOF) and depth of interaction (DOI) readouts, using GATE simulation and detection-based tasks using channelized Hotelling observer (CHO). Our simulation result indicates superior performance for detection of low-grade (3:1 lesion to tissue contrast), small (3 mm diameter) lesions using the proposed scanners compared to whole-body PET. We show that the incorporation of a DOI resolution of 2 mm substantially improves the detection tasks for the proposed scanner designs, while TOF capability is less impactful.