title: Estimation of articular cartilage properties using multivariate analysis of optical coherence tomography signal.
abstract: OBJECTIVE
  The aim was to investigate the applicability of multivariate analysis of optical coherence tomography (OCT) information for determining structural integrity, composition and mechanical properties of articular cartilage.
  
  
  METHODS
  Equine osteochondral samples (N = 65) were imaged with OCT, and their total attenuation and backscattering coefficients (μt and μb) were measured. Subsequently, the Mankin score, optical density (OD) describing the fixed charge density, light absorbance in amide I region (Aamide), collagen orientation, permeability, fibril network modulus (Ef) and non-fibrillar matrix modulus (Em) of the samples were determined. Partial least squares (PLS) regression model was calculated to predict tissue properties from the OCT signals of the samples.
  
  
  RESULTS
  Significant correlations between the measured and predicted mean collagen orientation (R(2) = 0.75, P < 0.0001), permeability (R(2) = 0.74, P < 0.0001), mean OD (R(2) = 0.73, P < 0.0001), Mankin scores (R(2) = 0.70, P < 0.0001), Em (R(2) = 0.50, P < 0.0001), Ef (R(2) = 0.42, P < 0.0001), and Aamide (R(2) = 0.43, P < 0.0001) were obtained. Significant correlation was also found between μb and Ef (ρ = 0.280, P = 0.03), but not between μt and any of the determined properties of articular cartilage (P > 0.05).
  
  
  CONCLUSIONS
  Multivariate analysis of OCT signal provided good estimates for tissue structure, composition and mechanical properties. This technique may significantly enhance OCT evaluation of articular cartilage integrity, and could be applied, for example, in delineation of degenerated areas around cartilage injuries during arthroscopic repair surgery.
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland; Department of Clinical Neurophysiology, Kuopio University Hospital, Kuopio, Finland. Electronic address: pia.puhakka@uef.fi.
authors.forename: P H
authors.initials: PH
authors.lastname: Puhakka
authors.affiliation: Department of Equine Sciences, Utrecht University, Utrecht, Netherlands. Electronic address: n.c.r.temoller@uu.nl.
authors.forename: N C R
authors.initials: NCR
authors.lastname: Te Moller
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland. Electronic address: isaac.afara@uef.fi.
authors.forename: I O
authors.initials: IO
authors.lastname: Afara
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland. Electronic address: janne.makela@uef.fi.
authors.forename: J T A
authors.initials: JTA
authors.lastname: Mäkelä
authors.affiliation: School of Medicine, Institute of Biomedicine, Anatomy, University of Eastern Finland, Kuopio, Finland. Electronic address: virpi.tiitu@uef.fi.
authors.forename: V
authors.initials: V
authors.lastname: Tiitu
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland. Electronic address: rami.korhonen@uef.fi.
authors.forename: R K
authors.initials: RK
authors.lastname: Korhonen
authors.affiliation: Department of Equine Sciences, Utrecht University, Utrecht, Netherlands. Electronic address: h.brommer@uu.nl.
authors.forename: H
authors.initials: H
authors.lastname: Brommer
authors.affiliation: Cancer Center, Kuopio University Hospital, Kuopio, Finland. Electronic address: tuomas.viren@kuh.fi.
authors.forename: T
authors.initials: T
authors.lastname: Virén
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland. Electronic address: jukka.jurvelin@uef.fi.
authors.forename: J S
authors.initials: JS
authors.lastname: Jurvelin
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland; Department of Clinical Neurophysiology, Kuopio University Hospital, Kuopio, Finland. Electronic address: juha.toyras@uef.fi.
authors.forename: J
authors.initials: J
authors.lastname: Töyräs
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000378:metabolism / Q000473:pathology*; D003094:Collagen / Q000378:metabolism; D006736:Horses; D016018:Least-Squares Analysis; D015999:Multivariate Analysis; D010539:Permeability; D017550:Spectroscopy, Fourier Transform Infrared; D041623:Tomography, Optical Coherence
chemical_list: D003094:Collagen
keywords: Articular cartilage; Degeneration; Optical coherence tomography; Partial least squares regression