title: Osteochondral repair: evaluation with sweep imaging with fourier transform in an equine model.
abstract: OBJECTIVE
  To evaluate the status of articular cartilage and bone in an equine model of spontaneous repair by using the sweep imaging with Fourier transform (SWIFT) magnetic resonance (MR) imaging technique.
  
  
  METHODS
  Experiments were approved by the Utrecht University Animal Ethics Committee. Six-millimeter-diameter chondral (n = 5) and osteochondral (n = 5, 3-4 mm deep into subchondral bone) defects were created in the intercarpal joints of seven 2-year-old horses and examined with SWIFT at 9.4 T after spontaneous healing for 12 months. Conventional T2 maps and gradient-echo images were obtained for comparison, and histologic assessment of cartilage and micro-computed tomography (CT) of bone were performed for reference. Signal-to-noise ratio (SNR) analysis was performed, and a radiologist evaluated the MR images. Structural bone parameters were derived from SWIFT and micro-CT datasets. Significance of differences was investigated with the Wilcoxon signed rank test and Pearson correlation analysis.
  
  
  RESULTS
  SWIFT was able to depict the different outcomes of spontaneous healing of focal chondral versus osteochondral defects. SWIFT produced constant signal intensity throughout cartilage, whereas T2 mapping showed elevated T2 values (P = .06) in repair tissue (mean T2 in superficial region of interest in an osteochondral lesion = 50.0 msec ± 10.2) in comparison to adjacent intact cartilage (mean T2 = 32.7 msec ± 4.2). The relative SNR in the subchondral plate with SWIFT (0.91) was more than four times higher than that with conventional fast spin-echo (0.12) and gradient-echo (0.19) MR imaging. The correlation between bone volume-to-tissue volume fractions determined with SWIFT and micro-CT was significant (r = 0.83, P < .01).
  
  
  CONCLUSIONS
  SWIFT enabled assessment of spontaneous osteochondral repair in an equine model.
authors.affiliation: Department of Applied Physics, A. I. Virtanen Institute for Molecular Sciences, and Institute of Biomedicine, Anatomy, University of Eastern Finland, PO Box 1627, 70211 Kuopio, Finland; Department of Equine Sciences, Faculty of Veterinary Medicine, University of Utrecht, Utrecht, the Netherlands; Department of Veterinary Clinical Sciences, School of Veterinary Medicine, University College Dublin, Dublin, Ireland; Center for Magnetic Resonance Research, Departments of Radiology and Orthopaedic Surgery, University of Minnesota, Minneapolis, Minn; Department of Orthopaedics and Traumatology, University of Helsinki and Helsinki University Central Hospital, Helsinki, Finland; Department of Orthopaedics and Traumatology, Jyväskylä Central Hospital, Jyväskylä, Finland; Department of Diagnostic Radiology, Institute of Diagnostics, University of Oulu, Oulu, Finland; Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland.
authors.forename: Jari
authors.initials: J
authors.lastname: Rautiainen
authors.forename: Lauri J
authors.initials: LJ
authors.lastname: Lehto
authors.forename: Virpi
authors.initials: V
authors.lastname: Tiitu
authors.forename: Outi
authors.initials: O
authors.lastname: Kiekara
authors.forename: Hertta
authors.initials: H
authors.lastname: Pulkkinen
authors.forename: Anne
authors.initials: A
authors.lastname: Brünott
authors.forename: René
authors.initials: R
authors.lastname: van Weeren
authors.forename: Harold
authors.initials: H
authors.lastname: Brommer
authors.forename: Pieter A J
authors.initials: PA
authors.lastname: Brama
authors.forename: Jutta
authors.initials: J
authors.lastname: Ellermann
authors.forename: Ilkka
authors.initials: I
authors.lastname: Kiviranta
authors.forename: Miika T
authors.initials: MT
authors.lastname: Nieminen
authors.forename: Mikko J
authors.initials: MJ
authors.lastname: Nissi
mesh_terms: D000465:Algorithms; D000818:Animals; D005583:Fourier Analysis; D017102:Fracture Healing; D050723:Fractures, Bone / Q000473:pathology*; D050724:Fractures, Cartilage / Q000473:pathology*; D006736:Horses; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007596:Joints / Q000293:injuries* / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity