title: Imaging large vessel vasculitis with fully integrated PET/MRI: a pilot study.
abstract: OBJECTIVE
  The 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.
  
  
  METHODS
  A 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.
  
  
  RESULTS
  TBRs, 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.
  
  
  CONCLUSIONS
  Hybrid PET/MRI is feasible in LVV and holds promise for precisely determining disease extent and disease activity.
authors: Department of Nuclear Medicine, Technische Universität München, Klinikum rechts der Isar, Ismaningerstr. 22, 81675, Munich, Germany, ingo.einspieler@tum.de.
authors: Ingo
authors: I
authors: Einspieler
authors: Klaus
authors: K
authors: Thürmel
authors: Thomas
authors: T
authors: Pyka
authors: Matthias
authors: M
authors: Eiber
authors: Sabine
authors: S
authors: Wolfram
authors: Philipp
authors: P
authors: Moog
authors: Christian
authors: C
authors: Reeps
authors: Markus
authors: M
authors: Essler
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001011:Aorta / Q000000981:diagnostic imaging; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D010865:Pilot Projects; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D014057:Tomography, X-Ray Computed; D014657:Vasculitis / Q000175:diagnosis / Q000000981:diagnostic imaging*
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18