Roy A. Raad MD, Presenter: Nothing to Disclose

Kent P. Friedman MD, Abstract Co-Author: Speaker, Bayer AG Spreaker, Spectrum Pharmaceuticals, Inc

Amy Noel Melsaether MD, Abstract Co-Author: Nothing to Disclose

James S. Babb PhD, Abstract Co-Author: Nothing to Disclose

Hersh Chandarana MD, Abstract Co-Author: Research support, Siemens AG

To assess outcomes of lung nodules missed on simultaneous positron emission tomography and magnetic resonance imaging (PET/MRI) in patients with known primary malignancy, with combined PET and computed tomography (PET/CT) as a reference

In this institutional review board-approved HIPAA-compliant retrospective study, 208 patients with known primary tumor undergoing clinically indicated 18-fluorodeoxyglucose (FDG) PET/CT followed by PET/MRI were initially reviewed. A single reader reviewed the thoracic station on PET/MR (radial T1 GRE (radial VIBE) with PET) and PET/CT, which included lung kernel CT reconstructions. Total of 88 small lung nodules (mean size 0.4 cm, range 0.2-1 cm) in 43 patients (11 males, 32 females, mean age 64.2 years, range 35-80 years) were detected only on the CT component of the PET/CT but were not identified on PET-MRI. None of these missed nodules demonstrated FDG uptake above background lung/mediastinal activity, and thus were considered non-avid. 84 /88 nodules were examined on follow-up (f/u) imaging with PET-CT or chest CT (mean f/u time 9.1 months, range 3-17 months). Remaining 4 nodules had no f/u imaging but had remote imaging studies available for comparison.

Among the 84 nodules that had f/u imaging, only 3 nodules (4%) in 1 patient progressed, 10 (12%) partially/completely resolved, whereas 71 (84%) remained stable in size and appearance. The 4 nodules that had no f/u were all stable since prior imaging 21-72 months prior, consistent with benignity. Furthermore, most (62/71, 87%) of the “stable” nodules were also stable since older studies over a total period of 11-78 months (mean 36.6 months), further confirming their benignity. None of the missed nodules changed patient management, including the 3 nodules (in 1 patient) that progressed on follow-up, in view of the patient’s extensive distant metastases.

PET-MRI remains a viable alternative imaging modality in oncology patients, despite its low sensitivity in detecting non-FDG avid small lung nodules. The vast majority (96%) of non-FDG avid lung nodules missed on PET-MRI compared to the reference PET-CT either resolved or remained stable on f/u imaging, consistent with benignity.

Compared to PET-CT, PET-MR has a lower diagnostic sensitivity in detecting small lung nodules. Assessment of the outcome of such nodules will help validate the utility of PET-MRI in oncology patients.

Raad, R, Friedman, K, Melsaether, A, Babb, J, Chandarana, H, Outcome of Small Lung Nodules Missed on Hybrid PET-MR: Institutional Experience with 43 Patients.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14011480.html