This study evaluates if retrospective software-fused magnetic resonance imaging/positron emission tomography (MRI/PET) images can improve concordance of MRI and PET/computed tomography (CT) findings in the pelvis and improve overall lesion detection and characterization, as compared with independent side-by-side interpretation of MRI and PET data sets. Institutional review board approval was obtained for this retrospective study. Our institution's electronic medical record system was examined for pelvic MRI scans and whole-body (18)F-fluorodeoxyglucose-PET/CT scans performed within a 2-month interval between January 2007 and June 2011. PET and MRI data sets for which there were discordant findings on original clinical reports were fused using software (Siemens TrueD, Erlangen, Germany). The fused MRI/PET data sets were reviewed by 2 radiologists for any evidence of metastatic disease in the pelvis. Interpretations were compared with original PET/CT and MRI reports (interpreted side by side), with pathology and imaging follow-up as the reference standard. Overall, 250 pairs of PET/CT and MRI scans were identified in 228 patients. A total of 57 discordant lesions were identified in 31 pairs of scans (12%) in 31 patients (14%). Software fusion resolved the discordance at 3 sites (5%) among 3 patients (10%), including 2 bone sites and a single nodal site. Software-fused MRI/PET is easy to perform and can increase the concordance rate of PET and MRI findings compared with side-by-side interpretation, thereby improving confidence in lesion characterization.
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