title: MR imaging of normal and matrix-depleted cartilage: correlation with biomechanical function and biochemical composition.
abstract: OBJECTIVE
  To correlate articular cartilage function, as reflected in biomechanical properties and biochemical composition, with magnetic resonance (MR) imaging parameters of normal articular cartilage and cartilage partially depleted of matrix components.
  
  
  METHODS
  Normal articular cartilage from 12 porcine patellae was evaluated biomechanically, biochemically, and with MR imaging (with and without gadolinium enhancement). The patellae were then enzymatically treated to deplete the matrix of either collagen or proteoglycan and then reevaluated biomechanically, biochemically, and with MR imaging. Correlations between cartilaginous tissue function and MR imaging parameters were made. Analysis of variance was performed to assess the effect of enzymatic treatment on measured parameters. Linear correlations among the MR imaging, biochemical, and biomechanical parameters were performed to determine the strengths of the relationships. P <.05 indicated statistically significant differences.
  
  
  RESULTS
  Biochemical, biomechanical, and MR analyses enabled detection of changes caused by matrix depletion (P <.05). T2 was the most useful MR imaging parameter for distinguishing proteoglycan loss from collagen loss. T2 correlated significantly with both biomechanical modulus (indicative of cartilage stiffness; P <.001, R2 = 0.51) and biochemical proteoglycan content (P <.001, R2 = 0.44). Differentiation between proteoglycan loss and collagen loss in terms of T1 improved with gadolinium enhancement. With gadolinium enhancement, proteoglycan depletion was associated with a greater decrease in T1 than collagen depletion (P <.05).
  
  
  CONCLUSIONS
  An association between biochemical and biomechanical functional status and MR imaging parameters of articular cartilage was demonstrated. Linear correlations existed between modulus and proteoglycan content in terms of T2. Additionally, proteoglycan loss and collagen loss had differing effects on gadolinium-enhanced T1 when it was expressed as the ratio of T1 after gadolinium enhancement/T1 before gadolinium enhancement.
authors.affiliation: Department of Biomedical Engineering, Virginia Commonwealth University, 1112 E Clay St, 325 McGuire Annex, PO Box 980694, Richmond, VA 23298, USA. jswayne@vcu.edu
authors.forename: Jennifer S
authors.initials: JS
authors.lastname: Wayne
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Kraft
authors.forename: Kelly J
authors.initials: KJ
authors.lastname: Shields
authors.forename: Chang
authors.initials: C
authors.lastname: Yin
authors.forename: John R
authors.initials: JR
authors.lastname: Owen
authors.forename: David G
authors.initials: DG
authors.lastname: Disler
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000737:chemistry* / Q000502:physiology*; D003094:Collagen / Q000378:metabolism; D003287:Contrast Media; D019786:Gadolinium DTPA; D008279:Magnetic Resonance Imaging; D010329:Patella; D011509:Proteoglycans / Q000378:metabolism; D013552:Swine
chemical_list: D003287:Contrast Media; D011509:Proteoglycans; D003094:Collagen; D019786:Gadolinium DTPA