title: Systematized water content calculation in cartilage using T1-mapping MR estimations: design and validation of a mathematical model.
abstract: BACKGROUND
  Up to 80 % of cartilage is water; the rest is collagen fibers and proteoglycans. Magnetic resonance (MR) T1-weighted measurements can be employed to calculate the water content of a tissue using T1 mapping. In this study, a method that translates T1 values into water content data was tested statistically.
  
  
  METHODS
  To develop a predictive equation, T1 values were obtained for tissue-mimicking gelatin samples. 1.5 T MRI was performed using inverse angle phase and an inverse sequence at 37 (±0.5) °C. Regions of interest were manually delineated and the mean T1 value was estimated in arbitrary units. Data were collected and modeled using linear regression. To validate the method, articular cartilage from six healthy pigs was used. The experiment was conducted in accordance with the Danish Animal Experiment Committee. Double measurements were performed for each animal. Ex vivo, all water in the tissue was extracted by lyophilization, thus allowing the volume of water to be measured. This was then compared with the predicted water content via Lin's concordance correlation coefficient at the 95 % confidence level.
  
  
  RESULTS
  The mathematical model was highly significant when compared to a null model (p < 0.0001). 97.3 % of the variation in water content can be explained by absolute T1 values. Percentage water content could be predicted as 0.476 + (T1 value) × 0.000193 × 100 %. We found that there was 98 % concordance between the actual and predicted water contents.
  
  
  CONCLUSIONS
  The results of this study demonstrate that MR data can be used to predict percentage water contents of cartilage samples.
  
  
  METHODS
  3 (case-control study).
authors: Orthopaedic Research Laboratory, Aarhus University Hospital NBG, Aarhus University, Noerrebrogade 44 Building 1A, 8000, Aarhus C, Denmark. jmshigue@gmail.com.
authors: J M
authors: JM
authors: Shiguetomi-Medina
authors: Department of Clinical Epidemiology and Public Health, Facultad de Medicina, Universidad Autónoma de San Luis Potosi, Venustiano Carranza 2045, 78210, San Luis Potosi, SLP, Mexico.
authors: J L
authors: JL
authors: Ramirez-Gl
authors: The MR Research Center, Aarhus University Hospital, Skejby, Brendstrupgaardsvej 100, 8200, Aarhus N, Denmark.
authors: H
authors: H
authors: Stødkilde-Jørgensen
authors: Department of Children's Orthopaedics, Aarhus University Hospital NBG, Noerrebrogade 44, 8000, Aarhus C, Denmark.
authors: B
authors: B
authors: Møller-Madsen
mesh_terms: D000818:Animals; D002356:Cartilage / Q000737:chemistry* / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging; D008954:Models, Biological; D013552:Swine; D014867:Water / Q000032:analysis*
chemical_list: D014867:Water
keywords: MR scanning; Mathematical model; Water content