• Ingo Einspieler, Klaus Thürmel, Thomas Pyka, Matthias Eiber, Sabine Wolfram, Philipp Moog, Christian Reeps, and Markus Essler.
• Department of Nuclear Medicine, Technische Universität München, Klinikum rechts der Isar, Ismaningerstr. 22, 81675, Munich, Germany, ingo.einspieler@tum.de.
• Eur. J. Nucl. Med. Mol. Imaging. 2015 Jun 1; 42 (7): 1012-24.

PurposeThe aim of this study was to evaluate the feasibility of hybrid [(18)F]fluorodeoxyglucose (FDG) positron emission tomography (PET)/MRI in patients with large vessel vasculitis (LVV) by comparing visual and quantitative parameters to that of PET/CT. Furthermore, the value of PET/MRI in disease activity and extent of LVV was assessed.MethodsA total of 16 [(18)F]FDG PET/MRI and 12 [(18)F]-FDG PET/CT examinations were performed in 12 patients with LVV. MRI of the vessel wall by T1-weighted and T2-weighted sequences was used for anatomical localization of FDG uptake and identification of morphological changes associated with LVV. In addition, contrast-enhanced (CE) magnetic resonance angiography (MRA) was performed. The vascular FDG uptake in the vasculitis group was compared to a reference group of 16 patients using a four-point visual score. Visual scores and quantitative parameters [maximum standardized uptake value (SUVmax) and target to background ratio (TBR)] were compared between PET/MRI and PET/CT. Furthermore, correlations between C-reactive protein (CRP) and quantitative PET results, as well the extent of vasculitis in PET, MRI/CE-MRA and combined PET/MRI, were analysed.ResultsTBRs, SUVmax values and visual scores correlated well between PET/MRI and PET/CT (r = 0.92, r = 0.91; r = 0.84, p < 0.05). There was no significant difference between both modalities concerning SUVmax measurements and visual scores. In PET/MRI, PET alone revealed abnormal FDG uptake in 86 vascular regions. MRI/CE-MRA indicated 49 vessel segments with morphological changes related to vasculitis, leading to a total number of 95 vasculitis regions in combination with PET. Strong and significant correlations between CRP and disease extent in PET alone (r = 0.75, p = 0.0067) and PET/MRI (r = 0.92, p < 0.0001) in contrast to MRI/CE-MRA only were observed. Regarding disease activity, no significant correlations were seen between quantitative PET results and CRP, although there was a trend towards significance (r = 0.55, p = 0.0651). PET/MRI also showed active LVV in 15/16 examinations.ConclusionHybrid PET/MRI is feasible in LVV and holds promise for precisely determining disease extent and disease activity.

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