PET/MR outperforms PET/CT in occult tumors

1526 Objectives To compare the diagnostic accuracy of PET/MR with PET/CT in patients with suspected occult primary tumors. Methods This prospective study was approved by the institutional review board. Sequential PET/CT-MR was performed in 43 patients (22 males, median age 58 years, range 20 - 86 years) referred for suspected occult primary tumors. Patients were assessed with PET/CT and PET/MR for the presence of a primary tumor, lymph node metastases and distant metastases. Wilcoxon signed-ranks test was performed to compare the diagnostic accuracy of PET/CT and PET/MR Results According to the standard of reference, a primary lesion was found in 14 patients. In 16 patients, the primary lesion remained occult. In the remaining 13 patients, lesions proved to be benign. PET/MR was superior to PET/CT for primary tumor detection (Sensitivity / specificity 0.85 / 0.97 vs. 0.69 / 0.73; p = 0.020), and comparable to PET/CT for the detection of lymph node metastases (Sensitivity / Specificity 0.93 / 1.00 vs. 0.93 / 0.93, p = 0.157) and distant metastases (Sensitivity / Specificity 1.00 / 0.97 vs. 0.82 / 1.00; p = 0.564). PET/CT tended to overestimate physiologic FDG uptake as malignancy compared with PET/MR (8 pt vs. 1 pt). Conclusions PET/MR outperforms PET/CT in the work-up of suspected occult malignancies. PET/MR may replace PET/CT to improve clinical workflow.