Feasibility of [18F]FDG PET/MRI with Early-Delayed and Extended PET as One-Stop Imaging for Staging and Predicting Metastasis in Rectal Cancer

We aimed to evaluate the diagnostic accuracy of 2-[18F]-fluoro-2-deoxy-D-glucose positron emission tomography/magnetic resonance imaging ([18F]FDG PET/MRI) for preoperative staging and usefulness of the detection of extramural vascular invasion (EMVI) for predicting metastasis in rectal cancer.Twenty-three patients underwent pretreatment [18F]FDG PET/MRI, including early-delayed and extended PET and dedicated pelvic MRI without using anticonvulsant or contrast agents. Seven patients received preoperative treatment and all subsequently underwent surgery. Clinical cancer stages were evaluated using postoperative histopathology as a reference. PET/MR-defined EMVI (pmrEMVI) and pathological (p) TN stages were correlated with disease progression for a maximum of 2 years.Of 16 patients without preoperative treatment, 10 had pT3, 4 tumors, 7 had pN1-3 lymph nodes, and 5 had synchronous metastases (SM; liver, lung, inguinal node). The sensitivity, specificity, and accuracy of PET/MRI were 90%, 67%, and 81% for T staging (T1, 2 vs. T3, 4), and 89%, 100%, and 94% for N staging (N0 vs. N1-3), respectively. Patient-based accuracy for SM staging was 100% (4/4). Of 23 patients, 6 were positive for pmrEMVI and 4 had metachronous metastases or local recurrence (MM; pelvic node, brain, lung, skin) during the follow-up periods. Five of the 6 pmrEMVI-positive patients had SM and/or MM (odds ratio = 37.5). Among pT, pN, and pmrEMVI, pmrEMVI-positivity was the only significant predictor for poorer progression-free survival (p < 0.05).[18F]FDG PET/MRI according to our suggested protocol is a one-stop, non-contrast, and valid diagnostic method for rectal cancer staging, and pmr-EMVI can be used as an imaging biomarker for predicting metastases.