PET/MR has proven more precise than PET/CT in a prospective study comparing the modalities on their in-practice utility for clarifying the workup of cancers of unknown primary origin, according to research published online Dec. 3 in Clinical Nuclear Medicine.
Tetsuro Sekine, MD, PhD, of the University of Zurich in Switzerland and Nippon Medical School in Japan and colleagues performed sequential PET/CT and PET/MR in 43 patients who were referred for suspected occult primary tumors.
The team assessed the patients (22 males, 21 females; median age, 58 years; range, 20-86 years) with the two modalities augmented by the contrast agent fludeoxyglucose (FDG), seeking the presence or absence of a primary tumor, lymph node metastases and/or distant metastases.
They found a primary lesion 14 patients. In 16 patients, the primary lesion remained occult, and, in the remaining 13, the lesions proved benign.
As for the comparison, PET/MR beat PET/CT at primary tumor detection (sensitivity/specificity, 0.85/0.97 vs. 0.69/0.73; P = 0.020).
It was 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).
And PET/CT “tended to misclassify physiologic uptake of FDG as malignancy compared with PET/MR (8 patients vs. 1 patient),” write the authors, whose specialties included nuclear medicine and neuroradiology as well as diagnostic and interventional radiology.
“PET/MR may replace PET/CT to improve clinical workflow,” they conclude.