Fully integrated [18F]FDG PET/MR in large vessel vasculitis

The aim of this study is to evaluate the usefulness of [¹⁸F] fluorodeoxyglucose (FDG) positron emission tomography (PET)/magnetic resonance (MR) in large vessels vasculitis (LVV) patients.

We performed an observational retrospective study based on our records. Images were acquired on a PET/MR scanner using [¹⁸F]FDG-PET whole body imaging. For each PET scan, a qualitative analysis and a semi-quantitative measure using the maximum of the standardized uptake value (SUVmax) were performed. SUVmax measurements normalized to the liver uptake were categorized using a grading scale. Vessel's wall thickness (WT) was measured at five fixed points (inferior margin of T5, T9, T12, L3, thickest area [max WT]).

Twenty-three LVV patients were included, 56.5% giant cells arteritis, 34.8% Takayasu's arteritis and 8.7% isolated aortitis, all Caucasian, mostly females (82%). We considered 32 PET scans for the LVV group (from a minimum of one to a maximum of three scans per patient) mainly during follow-up (29/32 scans), and 23 PET scans from a control group of non-metastatic malignancies patients. We found higher SUVmax compared to controls, in all sites, irrespective of clinical disease activity. Mean WT resulted higher in patients than in controls but was not correlated to SUVmax. Mean WT positively correlated with age in both cohorts, inversely correlated to disease duration, while no correlation with SUVmax was observed. The concordance between clinically active disease and PET hypermetabolism was poor (Cohen' κ=0.33).

PET/MR is a safe imaging technique capable of detecting inflammation in aortic wall. Low radiological exposure of PET/MR should be considered especially in young women receiving follow-up studies.