title: T2 values of articular cartilage in clinically relevant subregions of the asymptomatic knee.
abstract: OBJECTIVE
  In order for T2 mapping to become more clinically applicable, reproducible subregions and standardized T2 parameters must be defined. This study sought to: (1) define clinically relevant subregions of knee cartilage using bone landmarks identifiable on both MR images and during arthroscopy and (2) determine healthy T2 values and T2 texture parameters within these subregions.
  
  
  METHODS
  Twenty-five asymptomatic volunteers (age 18-35) were evaluated with a sagittal T2 mapping sequence. Manual segmentation was performed by three raters, and cartilage was divided into twenty-one subregions modified from the International Cartilage Repair Society Articular Cartilage Mapping System. Mean T2 values and texture parameters (entropy, variance, contrast, homogeneity) were recorded for each subregion, and inter-rater and intra-rater reliability was assessed.
  
  
  RESULTS
  The central regions of the condyles had significantly higher T2 values than the posterior regions (P < 0.05) and higher variance than the posterior region on the medial side (P < 0.001). The central trochlea had significantly greater T2 values than the anterior and posterior condyles. The central lateral plateau had lower T2 values, lower variance, higher homogeneity, and lower contrast than nearly all subregions in the tibia. The central patellar regions had higher entropy than the superior and inferior regions (each P ≤ 0.001). Repeatability was good to excellent for all subregions.
  
  
  CONCLUSIONS
  Significant differences in mean T2 values and texture parameters were found between subregions in this carefully selected asymptomatic population, which suggest that there is normal variation of T2 values within the knee joint. The clinically relevant subregions were found to be robust as demonstrated by the overall high repeatability.
authors.affiliation: Steadman Philippon Research Institute, 181 W Meadow Dr, Suite 1000, Vail, CO, 81657, USA, rachel.surowiec@sprivail.org.
authors.forename: Rachel K
authors.initials: RK
authors.lastname: Surowiec
authors.forename: Erin P
authors.initials: EP
authors.lastname: Lucas
authors.forename: Eric K
authors.initials: EK
authors.lastname: Fitzcharles
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Petre
authors.forename: Grant J
authors.initials: GJ
authors.lastname: Dornan
authors.forename: J Erik
authors.initials: JE
authors.lastname: Giphart
authors.forename: Robert F
authors.initials: RF
authors.lastname: LaPrade
authors.forename: Charles P
authors.initials: CP
authors.lastname: Ho
mesh_terms: D000293:Adolescent; D000328:Adult; D001182:Arthroscopy; D002358:Cartilage, Articular / Q000033:anatomy & histology* / Q000601:surgery; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007719:Knee Joint / Q000033:anatomy & histology* / Q000601:surgery; D008279:Magnetic Resonance Imaging; D008297:Male; D015203:Reproducibility of Results; D055815:Young Adult