title: Evaluation of 18F-fluoride PET/MR and PET/CT in patients with foot pain of unclear cause.
abstract: Our objective was to compare the quality and diagnostic performance of (18)F-fluoride PET/MR imaging with that of (18)F-fluoride PET/CT imaging in patients with foot pain of unclear cause.
  
  
  METHODS
  Twenty-two patients (9 men, 13 women; mean age, 48 ± 18 y; range, 20-78 y) were prospectively included in this study and underwent a single-injection dual-imaging protocol with (18)F-fluoride PET/CT and PET/MR. At a minimum, the PET/MR protocol included T1-weighted spin echo and proton-density fat-saturated sequences in 2 planes each with simultaneous acquisition of PET over 20 min. PET/CT included a native isotropic (0.6 mm) diagnostic CT scan (80 kV, 165 mAs) and a subsequent PET scan (2 min per bed position). By consensus, 2 masked interpreters randomly assessed both PET datasets for image quality (3-point scale) and for the presence of focal lesions with increased (18)F-fluoride uptake (maximum of 4 lesions). For each dataset (PET/CT vs. PET/MR), the diagnoses were defined using both PET and a morphologic dataset. Standardized uptake values (SUVs) from the 2 devices were compared using linear correlation and Bland-Altman plots. Moreover, we estimated the potential for dose reduction for PET/MR compared with PET/CT considering the longer acquisition time of PET/MR analyzing count rate statistics.
  
  
  RESULTS
  Image quality was rated diagnostic for both PET datasets. However, with a mean rating of 3.0/3 for PET/MR and 2.3/3 for PET/CT, image quality was significantly superior for PET/MR (P < 0.0001). The sensitivity of the PET datasets in PET/MR and PET/CT was equivalent, with the same 42 lesions showing focal (18)F-fluoride uptake. In PET/MR, the mean SUVmean was 10.4 (range, 2.0-67.7) and the mean SUVmax was 15.6 (range, 2.9-94.1). In PET/CT, the corresponding mean SUVmean of PET/CT was 10.2 (range, 1.8-55.6) and the mean SUVmax was 16.3 (range, 2.5-117.5), resulting in a high linear correlation coefficient (r = 0.96, P < 0.0001, for SUVmean and for SUVmax). A final consensus interpretation revealed the most frequent main diagnoses to be osteoarthritis, stress fracture, and bone marrow edema. PET/CT was more precise in visualizing osteoarthritis, whereas PET/MR was more specific in nondegenerative pathologies because of the higher soft-tissue and bone marrow contrast. The longer acquisition time of MR compared with CT would potentially allow (18)F-fluoride dose reduction using hybrid (18)F-fluoride PET/MR imaging of at least 50% according to the counting rate analysis.
  
  
  CONCLUSIONS
  In patients with foot pain of unclear cause, (18)F-fluoride PET/MR is technically feasible and is more robust in terms of image quality and SUV quantification than (18)F-fluoride PET/CT. In most patients, (18)F-fluoride PET/MR provided more diagnostic information at a higher diagnostic certainty than did PET/CT. Thus, PET/MR combines the high sensitivity of (18)F-fluoride PET to pinpoint areas with the dominant disease activity and the specificity of MR imaging for the final diagnosis with the potential for a substantial dose reduction compared with PET/CT.
authors: Department of Nuclear Medicine, Klinikum rechts der Isar, Technische Universität München, Munich, Germany isabel.rauscher@tum.de.
authors: Isabel
authors: I
authors: Rauscher
authors: Department of Nuclear Medicine, Klinikum rechts der Isar, Technische Universität München, Munich, Germany Department of Nuclear Medicine, University Hospital Ulm, Ulm, Germany.
authors: Ambros J
authors: AJ
authors: Beer
authors: Musculoskeletal Imaging, Department of Radiology, Kantonsspital Graubünden, Chur, Switzerland Department of Radiology, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
authors: Christoph
authors: C
authors: Schaeffeler
authors: Department of Nuclear Medicine, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
authors: Michael
authors: M
authors: Souvatzoglou
authors: Department of Trauma Surgery, Klinikum rechts der Isar, Technische Universität München, Munich, Germany; and.
authors: Moritz
authors: M
authors: Crönlein
authors: Department of Trauma Surgery, Klinikum rechts der Isar, Technische Universität München, Munich, Germany; and.
authors: Chlodwig
authors: C
authors: Kirchhoff
authors: Department of Trauma Surgery, Klinikum rechts der Isar, Technische Universität München, Munich, Germany; and.
authors: Gunther
authors: G
authors: Sandmann
authors: Department of Nuclear Medicine, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
authors: Sebastian
authors: S
authors: Fürst
authors: University of Applied Sciences Fresenius, Munich, Germany.
authors: Robert
authors: R
authors: Kilger
authors: Department of Nuclear Medicine, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
authors: Michael
authors: M
authors: Herz
authors: Department of Nuclear Medicine, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
authors: Sybille
authors: S
authors: Ziegler
authors: Department of Nuclear Medicine, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
authors: Markus
authors: M
authors: Schwaiger
authors: Department of Nuclear Medicine, Klinikum rechts der Isar, Technische Universität München, Munich, Germany.
authors: Matthias
authors: M
authors: Eiber
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D019788:Fluorodeoxyglucose F18; D005528:Foot / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D010146:Pain / Q000175:diagnosis*; D049268:Positron-Emission Tomography; D011446:Prospective Studies; D019275:Radiopharmaceuticals; D014057:Tomography, X-Ray Computed; D051598:Whole Body Imaging; D055815:Young Adult
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18
keywords: 18F-fluoride; PET/MR; foot pain