title: Reproducibility and regional variations of an improved gagCEST protocol for the in vivo evaluation of knee cartilage at 7 T.
abstract: OBJECTIVE
  The objective was to establish a gagCEST protocol that would enable robust and reproducible assessment of the glycosaminoglycan (GAG) content in knee cartilage at 7 T within a clinically feasible measurement time.
  
  
  METHODS
  Ten young healthy volunteers (mean age 26 years, range 24-28, five males, five females) were examined on a 7 T MR system. Informed consent was obtained from all individual participants prior to enrollment into the study. Each volunteer was measured twice for reproducibility assessment. The examined knee was immobilized using a custom-made fixation device. For the gagCEST measurement, a prototype segmented 3-D RF-spoiled gradient-echo sequence with an improved saturation scheme employing adiabatic pulses was used in a scan time of 19 min. The asymmetry of the Z-spectra (MTRasym) in selected regions of interest in knee cartilage was calculated. Differences in MTRasym between different regions were evaluated using ANOVA and the Bonferroni corrected post hoc test.
  
  
  RESULTS
  The improvement of the saturation scheme reduced the influence of field inhomogeneities, resulted in more uniform saturation, and allowed for good reproducibility in a reasonable measurement time (19 min), as demonstrated by an intraclass correlation coefficient of 0.77. Improved fixation helped to reduce motion artifacts. Whereas similar MTRasym values were found for weight-bearing and non-weight-bearing femoral cartilage, lower values were observed in the trochlear groove (p = 0.028), patellar (p = 0.015) and tibial cartilage (p < 0.001) when compared to non-weight-bearing femoral cartilage.
  
  
  CONCLUSIONS
  Reasonable reproducibility and sensitivity to regional differences in GAG content suggests that the improved gagCEST protocol might be useful for assessing the biochemical changes in articular cartilage that are associated with early stages of cartilage degeneration.
authors.affiliation: Department of Orthopaedic Surgery, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria.|Department of Biomedical Imaging and Image-Guided Therapy, High Field MR Centre, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria.
authors.forename: Markus M
authors.initials: MM
authors.lastname: Schreiner
authors.affiliation: Department of Biomedical Imaging and Image-Guided Therapy, High Field MR Centre, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria.
authors.forename: Štefan
authors.initials: Š
authors.lastname: Zbýň
authors.affiliation: Healthcare Sector, Siemens Ltd. Australia, Macquarie Park, NSW, Australia.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Schmitt
authors.affiliation: Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Weber
authors.affiliation: Department of Orthopaedic Surgery, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria.
authors.forename: Stephan
authors.initials: S
authors.lastname: Domayer
authors.affiliation: Department of Orthopaedic Surgery, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Windhager
authors.affiliation: Department of Biomedical Imaging and Image-Guided Therapy, High Field MR Centre, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria. siegfried.trattnig@meduniwien.ac.at.
authors.forename: Siegfried
authors.initials: S
authors.lastname: Trattnig
authors.affiliation: Department of Biomedical Imaging and Image-Guided Therapy, High Field MR Centre, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Mlynárik
mesh_terms: D000328:Adult; D016477:Artifacts; D002358:Cartilage, Articular / Q000000981:diagnostic imaging* / Q000473:pathology; D005260:Female; D006025:Glycosaminoglycans / Q000737:chemistry*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007717:Knee / Q000000981:diagnostic imaging* / Q000473:pathology; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009038:Motion; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D006025:Glycosaminoglycans
keywords: 7 T; CEST; Cartilage; Glycosaminoglycans; Knee joint