title: Correlation between apparent diffusion coefficient and viscoelasticity of articular cartilage in a porcine model.
abstract: OBJECTIVE
  Quantitative MR imaging techniques of degenerative cartilage have been reported as useful indicators of degenerative changes in cartilage extracellular matrix, which consists of proteoglycans, collagen, non-collagenous proteins, and water. Apparent diffusion coefficient (ADC) mapping of cartilage has been shown to correlate mainly with the water content of the cartilage. As the water content of the cartilage in turn correlates with its viscoelasticity, which directly affects the mechanical strength of articular cartilage, ADC can serve as a potentially useful indicator of the mechanical strength of cartilage. The aim of this study was to investigate the correlation between ADC and viscoelasticity as measured by indentation testing.
  
  
  METHODS
  Fresh porcine knee joints (n = 20, age 6 months) were obtained from a local abattoir. ADC of porcine knee cartilage was measured using a 3-Tesla MRI. Indentation testing was performed on an electromechanical precision-controlled system, and viscosity coefficient and relaxation time were measured as additional indicators of the viscoelasticity of cartilage. The relationship between ADC and viscosity coefficient as well as that between ADC and relaxation time were assessed.
  
  
  RESULTS
  ADC was correlated with relaxation time and viscosity coefficient (R(2) = 0.75 and 0.69, respectively, p < 0.01). The mean relaxation time values in the weight-bearing and non-weight-bearing regions were 0.61 ± 0.17 ms and 0.14 ± 0.08 ms, respectively.
  
  
  CONCLUSIONS
  This study found a moderate correlation between ADC and viscoelasticity in the superficial articular cartilage. Both molecular diffusion and viscoelasticity were higher in weight bearing than non-weight-bearing articular cartilage areas.
authors.affiliation: Department of Radiological Science, Graduate School of Human Health Science, Tokyo Metropolitan University, 7-2-10 Higashiogu, Arakawa-ku, Tokyo, Japan. aoki-takako@hs.tmu.ac.jp
authors.forename: T
authors.initials: T
authors.lastname: Aoki
authors.forename: A
authors.initials: A
authors.lastname: Watanabe
authors.forename: N
authors.initials: N
authors.lastname: Nitta
authors.forename: T
authors.initials: T
authors.lastname: Numano
authors.forename: M
authors.initials: M
authors.lastname: Fukushi
authors.forename: M
authors.initials: M
authors.lastname: Niitsu
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000033:anatomy & histology* / Q000502:physiology*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D055119:Elastic Modulus / Q000502:physiology; D066298:In Vitro Techniques; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013223:Statistics as Topic; D013552:Swine; D014783:Viscosity; D016474:Weight-Bearing / Q000502:physiology*