title: High resolution MRI imaging at 9.4 Tesla of the osteochondral unit in a translational model of articular cartilage repair.
abstract: BACKGROUND
  Non-destructive structural evaluation of the osteochondral unit is challenging. Here, the capability of high-field magnetic resonance imaging (μMRI) at 9.4 Tesla (T) was explored to examine osteochondral repair ex vivo in a preclinical large animal model. A specific aim of this study was to detect recently described alterations of the subchondral bone associated with cartilage repair.
  
  
  METHODS
  Osteochondral samples of medial femoral condyles from adult ewes containing full-thickness articular cartilage defects treated with marrow stimulation were obtained after 6 month in vivo and scanned in a 9.4 T μMRI. Ex vivo imaging of small osteochondral samples (typical volume: 1-2 cm(3)) at μMRI was optimised by variation of repetition time (TR), time echo (TE), flip angle (FA), spatial resolution and number of excitations (NEX) from standard MultiSliceMultiEcho (MSME) and three-dimensional (3D) spoiled GradientEcho (SGE) sequences.
  
  
  RESULTS
  A 3D SGE sequence with the parameters: TR = 10 ms, TE = 3 ms, FA = 10°, voxel size = 120 × 120 × 120 μm(3) and NEX = 10 resulted in the best fitting for sample size, image quality, scanning time and artifacts. An isovolumetric voxel shape allowed for multiplanar reconstructions. Within the osteochondral unit articular cartilage, cartilaginous repair tissue and bone marrow could clearly be distinguished from the subchondral bone plate and subarticular spongiosa. Specific alterations of the osteochondral unit associated with cartilage repair such as persistent drill holes, subchondral bone cysts, sclerosis of the subchondral bone plate and of the subarticular spongiosa and intralesional osteophytes were precisely detected.
  
  
  CONCLUSIONS
  High resolution, non-destructive ex vivo analysis of the entire osteochondral unit in a preclinical large animal model that is sufficient for further analyses is possible using μMRI at 9.4 T. In particular, 9.4 T is capable of accurately depicting alterations of the subchondral bone that are associated with osteochondral repair.
authors.affiliation: Center of Experimental Orthopaedics, Saarland University Medical Center, Kirrberger Straße, Building 37, Homburg/Saar, D-66421, Germany. Lars.Goebel@uks.eu.|Department of Orthopaedic Surgery, Saarland University Medical Center, Kirrberger Straße, Building 37, Homburg/Saar, D-66421, Germany. Lars.Goebel@uks.eu.|Cartilage Net of the Greater Region, University of the Greater Region, Homburg/Saar, D-66421, Germany. Lars.Goebel@uks.eu.
authors.forename: Lars
authors.initials: L
authors.lastname: Goebel
authors.affiliation: Department of Diagnostic and Interventional Radiology, Saarland University Medical Center, Kirrberger Straße, Building 57, Homburg/Saar, D-66421, Germany. andreas.mueller@uks.eu.
authors.forename: Andreas
authors.initials: A
authors.lastname: Müller
authors.affiliation: Department of Diagnostic and Interventional Radiology, Saarland University Medical Center, Kirrberger Straße, Building 57, Homburg/Saar, D-66421, Germany. Arno.Buecker@uks.eu.
authors.forename: Arno
authors.initials: A
authors.lastname: Bücker
authors.affiliation: Center of Experimental Orthopaedics, Saarland University Medical Center, Kirrberger Straße, Building 37, Homburg/Saar, D-66421, Germany. henning.madry@uks.eu.|Department of Orthopaedic Surgery, Saarland University Medical Center, Kirrberger Straße, Building 37, Homburg/Saar, D-66421, Germany. henning.madry@uks.eu.|Cartilage Net of the Greater Region, University of the Greater Region, Homburg/Saar, D-66421, Germany. henning.madry@uks.eu.
authors.forename: Henning
authors.initials: H
authors.lastname: Madry
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000473:pathology* / Q000601:surgery*; D005260:Female; D005269:Femur / Q000473:pathology* / Q000601:surgery*; D008279:Magnetic Resonance Imaging / Q000379:methods / Q000592:standards*; D023421:Models, Animal; D012756:Sheep; D014945:Wound Healing