title: T1ρ Dispersion in Articular Cartilage: Relationship to Material Properties and Macromolecular Content.
abstract: OBJECTIVE
  This study assessed T1ρ relaxation dispersion, measured by magnetic resonance imaging (MRI), as a tool to noninvasively evaluate cartilage material and biochemical properties. The specific objective was to answer two questions: (1) does cartilage initial elastic modulus (E 0) correlate with T1ρ dispersion effects and (2) does collagen or proteoglycan content correlate with T1ρ dispersion effects?
  
  
  METHODS
  Cadaveric patellae with and without visible cartilage damage on conventional MR were included. T2 and T1ρ relaxation times at 500 and 1000 Hz spin-lock field amplitudes were measured. We estimated T1ρ dispersion effects by measuring T1ρ relaxation time at 500 and 1000 Hz and T2 relaxation time and using a new tool, the ratio T1ρ/T2. Cartilage initial elastic modulus, E 0, was measured from initial response of mechanical indentation creep tests. Collagen and proteoglycan contents were measured at the indentation test sites; proteoglycan content was measured by their covalently linked sulfated glycosaminoglycans (sGAG). Pearson correlation coefficients were determined, taking into account the clustering of multiple samples within a single patella specimen.
  
  
  RESULTS
  Cartilage initial elastic modulus, E 0, increased with decreasing values of T1ρ/T2 measurements at both 500 Hz (P = 0.034) and 1000 Hz (P = 0.022). 1/T1ρ relaxation time (500 Hz) increased with increasing sGAG content (P = 0.041).
  
  
  CONCLUSIONS
  T1ρ/T2 ratio, a new tool, and cartilage initial elastic modulus are both measures of water-protein interactions, are dependent on the cartilage structure, and were correlated in this study.
authors.affiliation: Department of Mechanical Engineering, Stanford University, Stanford, CA, USA.
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Keenan
authors.affiliation: Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand.
authors.forename: Thor F
authors.initials: TF
authors.lastname: Besier
authors.affiliation: Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, CA, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Pauly
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, CA, USA ; Rehabilitation R&D Musculoskeletal Research Laboratory, Department of Veterans Affairs, Palo Alto, CA, USA.
authors.forename: R Lane
authors.initials: RL
authors.lastname: Smith
authors.affiliation: Department of Mechanical Engineering, Stanford University, Stanford, CA, USA ; Department of Bioengineering, Stanford University, Stanford, CA, USA.
authors.forename: Scott L
authors.initials: SL
authors.lastname: Delp
authors.affiliation: Rehabilitation R&D Musculoskeletal Research Laboratory, Department of Veterans Affairs, Palo Alto, CA, USA.
authors.forename: Gary S
authors.initials: GS
authors.lastname: Beaupre
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, CA, USA ; Department of Bioengineering, Stanford University, Stanford, CA, USA ; Department of Radiology, Stanford University, Stanford, CA, USA.
authors.forename: Garry E
authors.initials: GE
authors.lastname: Gold
keywords: T1ρ dispersion; articular cartilage; collagen; initial elastic modulus; proteoglycan