title: Chemical exchange in knee cartilage assessed by R1ρ (1/T1ρ) dispersion at 3T.
abstract: OBJECTIVE
  To quantify the characteristics of proton chemical exchange in knee cartilage in vivo by R1ρ dispersion analysis.
  
  
  METHODS
  Six healthy subjects (one female and five males, age range 24 to 71 y) underwent T1ρ imaging of knee cartilage on a 3T MRI scanner. Quantitative estimates of R1ρ (=1/T1ρ) were made using 5 different spin-lock durations for each of 12 different spin-lock amplitudes over the range 0 to 550Hz. When the variations of R1ρ with spin-locking strength (the R1ρ dispersion) are dominated by chemical exchange contributions, R1ρ dispersion curves can be analyzed to derive quantitative characteristics of the exchange and provide information on tissue composition. In this work, in vivo R1ρ dispersion of human knee articular cartilage at 3T was analyzed, and the exchange rates of protons between water and macromolecular hydroxyls (mainly in glycosaminoglycans) were estimated based on a theoretical model.
  
  
  RESULTS
  R1ρ values showed marked dispersion in articular cartilage and varied by approximately 50% between low and high values of the locking field, a change much greater than in surrounding tissues, consistent with greater contributions from chemical exchange. From the theoretical model, the exchange rates in cartilage were estimated to be in the range of 1.0-3.0kHz, and varied within the tissue. Variations within a single knee appear to be larger with increasing age.
  
  
  CONCLUSIONS
  R1ρ dispersion analysis may provide more specific information for studying cartilage biochemical composition and form the basis for quantitative evaluation of cartilage disorders.
authors.affiliation: Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA. Electronic address: p.wang@vanderbilt.edu.
authors.forename: Ping
authors.initials: P
authors.lastname: Wang
authors.affiliation: Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA.
authors.forename: Jake
authors.initials: J
authors.lastname: Block
authors.affiliation: Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA.
authors.forename: John C
authors.initials: JC
authors.lastname: Gore
mesh_terms: D000328:Adult; D000368:Aged; D002358:Cartilage, Articular / Q000473:pathology*; D005260:Female; D006025:Glycosaminoglycans / Q000737:chemistry; D064368:Healthy Volunteers; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007717:Knee / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D014867:Water / Q000737:chemistry
chemical_list: D006025:Glycosaminoglycans; D014867:Water
keywords: Articular cartilage; CEST; R(1ρ) dispersion; T(1ρ)
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