title: Adiabatic rotating frame relaxation of MRI reveals early cartilage degeneration in a rabbit model of anterior cruciate ligament transection.
abstract: OBJECTIVE
  To investigate the sensitivity of seven quantitative magnetic resonance imaging (MRI) parameters (adiabatic T1ρ, adiabatic T2ρ, continuous wave (CW) T1ρ, relaxation along a fictitious field (RAFF), T2 measured with adiabatic double echo (DE) and Carr-Purcell-Meiboom-Gill (CPMG) sequence, and T1 during off-resonance saturation [magnetization transfer (MT)]) to detect early osteoarthritic changes in a rabbit model of anterior cruciate ligament transection (ACLT).
  
  
  METHODS
  ACLT was unilaterally induced in the knees of New Zealand White rabbits (n = 8) while contralateral joints served as controls. Femoral condyles of the joints were harvested 4 weeks post-ACLT. MRI was performed at 9.4 T. For reference, quantitative histology, Mankin grading and biomechanical measurements were conducted.
  
  
  RESULTS
  Reference methods demonstrated early, superficial cartilage degeneration in the ACLT group, including significant loss of proteoglycans in both medial and lateral compartments, increased collagen fibril anisotropy in the lateral condyle and decreased biomechanical properties at both medial and lateral compartments. CW-T1ρ was prolonged in the lateral compartment of ACLT joints while adiabatic T1ρ and T2ρ detected degenerative changes in tissue in both lateral and medial condyles (P < 0.05). DE-T2 was significantly (P < 0.05) elevated only in the lateral compartment while CPMG-T2, MT or RAFF did not show a statistically significant difference between the groups.
  
  
  CONCLUSIONS
  Adiabatic T1ρ and T2ρ relaxation times detected most sensitively early degenerative changes in cartilage 4 weeks post-ACLT in a rabbit model.
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland; Department of Diagnostic Radiology, University of Oulu, Oulu, Finland; Medical Research Center Oulu, University of Oulu, Oulu, Finland. Electronic address: jari.rautiainen@uef.fi.
authors.forename: J
authors.initials: J
authors.lastname: Rautiainen
authors.affiliation: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland; Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, United States; Department of Orthopaedic Surgery, University of Minnesota, Minneapolis, MN, United States. Electronic address: nissi@cmrr.umn.edu.
authors.forename: M J
authors.initials: MJ
authors.lastname: Nissi
authors.affiliation: A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland. Electronic address: timo.liimatainen@uef.fi.
authors.forename: T
authors.initials: T
authors.lastname: Liimatainen
authors.affiliation: Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada. Electronic address: walter@kin.ucalgary.ca.
authors.forename: W
authors.initials: W
authors.lastname: Herzog
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 Diagnostic Radiology, University of Oulu, Oulu, Finland; Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland. Electronic address: miika.nieminen@oulu.fi.
authors.forename: M T
authors.initials: MT
authors.lastname: Nieminen
mesh_terms: D000818:Animals; D000070598:Anterior Cruciate Ligament Injuries; D002357:Cartilage Diseases / Q000473:pathology*; D002358:Cartilage, Articular / Q000473:pathology*; D004195:Disease Models, Animal; D007719:Knee Joint / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011817:Rabbits; D012680:Sensitivity and Specificity
keywords: ACLT; Articular cartilage; MRI; Osteoarthritis; Rabbit model