title: Quantitative assessment of atherosclerotic plaques on (18)F-FDG PET/MRI: comparison with a PET/CT hybrid system.
abstract: OBJECTIVE
  PET with (18)F-FDG has the potential to assess vascular macrophage metabolism. (18)F-FDG is most often used in combination with contrast-enhanced CT to localize increased metabolism to specific arterial lesions. Novel (18)F-FDG PET/MRI hybrid imaging shows high potential for the combined evaluation of atherosclerotic plaques, due to the superior morphological conspicuity of plaque lesions. The purpose of this study was to evaluate the reliability and accuracy of (18)F-FDG PET/MRI uptake quantification compared to PET/CT as a reference standard in patients with carotid atherosclerotic plaques.
  
  
  METHODS
  The study group comprised 34 consecutive oncological patients with carotid plaques who underwent both PET/CT and PET/MRI with (18)F-FDG on the same day. The presence of atherosclerotic plaques was confirmed by 3 T MRI scans. Maximum standardized uptake values (SUVmax) for carotid plaque lesions and the average SUV of the blood pool within the adjacent internal jugular vein were determined and target-to-blood ratios (TBRs, plaque to blood pool) were calculated.
  
  
  RESULTS
  Atherosclerotic lesions with maximum colocalized focal FDG uptake were assessed in each patient. SUVmax values of carotid plaque lesions were significantly lower on PET/MRI than on PET/CT (2.3 ± 0.6 vs. 3.1 ± 0.6; P < 0.01), but were significantly correlated between PET/CT and PET/MRI (Spearman's r = 0.67, P < 0.01). In contrast, TBRmax values of plaque lesions were similar on PET/MRI and on PET/CT (2.2 ± 0.3 vs. 2.2 ± 0.3; P = 0.4), and again were significantly correlated between PET/MRI and PET/CT (Spearman's r = 0.73, P < 0.01). Considering the increasing trend in SUVmax and TBRmax values from early to delayed imaging time-points on PET/CT and PET/MRI, respectively, with continuous clearance of radioactivity from the blood, a slight underestimation of TBRmax values may also be expected with PET/MRI compared with PET/CT.
  
  
  CONCLUSIONS
  SUVmax and TBRmax values are widely accepted reference parameters for estimation of the radioactivity of atherosclerotic plaques on PET/CT. However, due to a systematic underestimation of SUVmax and TBRmax with PET/MRI, the optimal cut-off values indicating the presence of inflamed plaque tissue need to be newly defined for PET/MRI.
authors.affiliation: Division of Nuclear Medicine, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria.
authors.forename: Xiang
authors.initials: X
authors.lastname: Li
authors.affiliation: Division of Nuclear Medicine, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria.
authors.forename: Daniel
authors.initials: D
authors.lastname: Heber
authors.affiliation: Center for Medical Physics and Biomedical Engineering, General Hospital Vienna, Medical University of Vienna, Vienna, Austria.
authors.forename: Ivo
authors.initials: I
authors.lastname: Rausch
authors.affiliation: Division of Cardiovascular and Interventional Radiology, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.
authors.forename: Dietrich
authors.initials: D
authors.lastname: Beitzke
authors.affiliation: Division of General and Pediatric Radiology, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.
authors.forename: Marius E
authors.initials: ME
authors.lastname: Mayerhoefer
authors.affiliation: Division of Nuclear Medicine, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria.
authors.forename: Sazan
authors.initials: S
authors.lastname: Rasul
authors.affiliation: Department of Nuclear Medicine, Klinikum Augsburg, Augsburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Kreissl
authors.affiliation: Division of Nuclear Medicine, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria.
authors.forename: Markus
authors.initials: M
authors.lastname: Mitthauser
authors.affiliation: Division of Nuclear Medicine, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wadsak
authors.affiliation: Division of Nuclear Medicine, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria.
authors.forename: Markus
authors.initials: M
authors.lastname: Hartenbach
authors.affiliation: Division of Nuclear Medicine, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria.
authors.forename: Alexander
authors.initials: A
authors.lastname: Haug
authors.affiliation: Department of Nuclear Medicine, State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center for Cardiovascular Diseases, Beijing, China.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Division of Cardiovascular and Interventional Radiology, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria.
authors.forename: Christian
authors.initials: C
authors.lastname: Loewe
authors.affiliation: Center for Medical Physics and Biomedical Engineering, General Hospital Vienna, Medical University of Vienna, Vienna, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Beyer
authors.affiliation: Division of Nuclear Medicine, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria. marcus.hacker@meduniwien.ac.at.
authors.forename: Marcus
authors.initials: M
authors.lastname: Hacker
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002340:Carotid Artery Diseases / Q000000981:diagnostic imaging; D016893:Carotid Stenosis / Q000000981:diagnostic imaging; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D058226:Plaque, Atherosclerotic / Q000000981:diagnostic imaging*; D000072078:Positron Emission Tomography Computed Tomography; D015203:Reproducibility of Results
chemical_list: D019788:Fluorodeoxyglucose F18
keywords: 18F-FDG; Atherosclerosis; Carotid plaque; Inflammation; PET/CT; PET/MRI
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