title: T(2) relaxation time mapping reveals age- and species-related diversity of collagen network architecture in articular cartilage.
abstract: OBJECTIVE
  The magnetic resonance imaging (MRI) parameter T(2) relaxation time has been shown to be sensitive to the collagen network architecture of articular cartilage. The aim of the study was to investigate the agreement of T(2) relaxation time mapping and polarized light microscopy (PLM) for the determination of histological properties (i.e., zone and fibril organization) of articular cartilage.
  
  
  METHODS
  T(2) relaxation time was determined at 9.4 T field strength in healthy adult human, juvenile bovine and juvenile porcine patellar cartilage, and related to collagen anisotropy and fibril angle as measured by quantitative PLM.
  
  
  RESULTS
  Both T(2) and PLM revealed a mutually consistent but varying number of collagen-associated laminae (3, 3-5 or 3-7 laminae in human, porcine and bovine cartilage, respectively). Up to 44% of the depth-wise variation in T(2) was accounted for by the changing anisotropy of collagen fibrils, confirming that T(2) contrast of articular cartilage is strongly affected by the collagen fibril anisotropy. A good correspondence was observed between the thickness of T(2)-laminae and collagenous zones as determined from PLM anisotropy measurements (r=0.91, r=0.95 and r=0.91 for human, bovine and porcine specimens, respectively).
  
  
  CONCLUSIONS
  According to the present results, T(2) mapping is capable of detecting histological differences in cartilage collagen architecture among species, likely to be strongly related to the differences in maturation of the tissue. This diversity in the MRI appearance of healthy articular cartilage should also be recognized when using juvenile animal tissue as a model for mature human cartilage in experimental studies.
authors.affiliation: Department of Physics, University of Kuopio, Kuopio, Finland. nissi@venda.uku.fi
authors.forename: M J
authors.initials: MJ
authors.lastname: Nissi
authors.forename: J
authors.initials: J
authors.lastname: Rieppo
authors.forename: J
authors.initials: J
authors.lastname: Töyräs
authors.forename: M S
authors.initials: MS
authors.lastname: Laasanen
authors.forename: I
authors.initials: I
authors.lastname: Kiviranta
authors.forename: J S
authors.initials: JS
authors.lastname: Jurvelin
authors.forename: M T
authors.initials: MT
authors.lastname: Nieminen
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism / Q000473:pathology*; D000818:Animals; D016880:Anisotropy; D002358:Cartilage, Articular / Q000033:anatomy & histology* / Q000737:chemistry; D002417:Cattle; D003094:Collagen / Q000378:metabolism*; D024021:Fibril-Associated Collagens / Q000378:metabolism; D006801:Humans; D007719:Knee Joint / Q000737:chemistry / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008859:Microscopy, Polarization; D008875:Middle Aged; D010329:Patella / Q000033:anatomy & histology / Q000737:chemistry; D013045:Species Specificity; D013552:Swine
chemical_list: D024021:Fibril-Associated Collagens; D003094:Collagen