Outcome of small lung nodules missed on hybrid PET/MRI in patients with primary malignancy

Purpose To assess outcomes of lung nodules missed on simultaneous positron emission tomography and magnetic resonance imaging (PET/MRI) compared to the reference standard PET and computed tomography (PET/CT) in patients with primary malignancy. Materials and Methods In all, 208 patients with primary malignancy undergoing clinically indicated ( 18 F) fluorodeoxyglucose (FDG) PET/CT followed by PET/MRI were independently reviewed by two readers. Upon review of the thoracic station on PET/MRI and PET/CT, 89 non‐FDG avid small lung nodules in 43 patients were detected (by reader 1) only on the CT component of the PET/CT but were not identified on PET/MRI. Overall, 84 of these 89 nodules were examined on follow‐up imaging with PET/CT or chest CT. The remaining five nodules had no follow‐up imaging but had remote imaging available for comparison. Results Among the 84 nodules with follow‐up, three nodules (3%) in one patient progressed, 10 (12%) nodules partially/completely resolved, whereas 71 nodules (85%) remained stable. The five nodules without follow‐up were all stable since prior imaging of over 21 months. Conclusion The vast majority (97%) of small non‐FDG avid lung nodules missed on PET/MRI either resolved or remained stable on follow‐up, suggestive of benignity. PET/MRI remains a viable alternative imaging modality in oncology patients, despite its low sensitivity in detecting small lung nodules. J. Magn. Reson. Imaging 2016;43:504–511.