title: On Subregional Analysis of Cartilage Loss from Knee MRI.
abstract: OBJECTIVE
  Understanding how knee cartilage is affected by osteoarthritis (OA) is critical in the development of sensitive biomarkers that may be used as surrogate endpoints in clinical trials. The objective of this study was to analyze longitudinal changes in cartilage thickness using detailed change maps and to examine if current methods for subregional analysis are able to capture the underlying cartilage changes.
  
  
  METHODS
  MRI images of 267 knees from 135 participants were acquired at baseline and 21-month follow-up and processed using a fully automatic framework for cartilage segmentation and quantification. The framework provides an anatomical coordinate system that allows for direct comparison across cartilage thickness maps. The reproducibility of this method was evaluated on 37 scan-rescan image pairs.
  
  
  RESULTS
  In OA knees, an annualized thickness loss of 3.7% was observed in the medial femoral cartilage plate (MF) whereas subregional measurements varied between -9.0% (loss) and 1.6%. The largest changes were observed in the posterior part of the MF. In the medial tibial cartilage plate (MT), a thickness increase of 0.4% was observed whereas subregional measurements varied between -0.8% (loss) and 1.6%. In addition, notable differences in the patterns of cartilage change were observed between genders.
  
  
  CONCLUSIONS
  This study indicated that the spatial changes, although highly heterogeneous, showed distinct patterns of cartilage thinning and cartilage thickening in both the MF and the MT. These patterns were not accurately reflected when thickness changes were averaged over large, predefined subregions as defined in current methods for subregional analysis.
authors.affiliation: Department of Computer Science, University of Copenhagen, Copenhagen, Denmark ; Biomediq A/S, Copenhagen, Denmark.
authors.forename: Dan R
authors.initials: DR
authors.lastname: Jørgensen
authors.affiliation: Biomediq A/S, Copenhagen, Denmark.
authors.forename: Martin
authors.initials: M
authors.lastname: Lillholm
authors.affiliation: Synarc Inc., Newark, CA, USA.
authors.forename: Harry K
authors.initials: HK
authors.lastname: Genant
authors.affiliation: Biomediq A/S, Copenhagen, Denmark.
authors.forename: Erik B
authors.initials: EB
authors.lastname: Dam
keywords: cartilage thickness; knee MRI; longitudinal; osteoarthritis