title: T2 relaxation time of cartilage at MR imaging: comparison with severity of knee osteoarthritis.
abstract: OBJECTIVE
  To evaluate differences in T2 values in femoral and tibial cartilage at magnetic resonance (MR) imaging in patients with varying degrees of osteoarthritis (OA) compared with healthy subjects and to develop a mapping and display method based on calculation of T2 z scores for visual grading and assessment of cartilage heterogeneity in patients with OA.
  
  
  METHODS
  Knee cartilage was evaluated in 55 subjects who were categorized with radiography as healthy (n = 7) or as having mild OA (n = 20) or severe OA (n = 28). Cartilage regions were determined with manual segmentation of an MR image acquired with spoiled gradients and fat suppression. The segmentation was applied to a map of T2 relaxation time and was analyzed in four knee cartilage compartments (ie, the medial and lateral tibia and femur). Differences between cartilage compartment T2 values and subject groups were analyzed with analysis of covariance. Correlations of cartilage T2 values with clinically reported symptoms and cartilage thickness and volume were examined. Cartilage T2 values were converted to z scores per voxel on the basis of normal population values in the same cartilage compartment to better interpret cartilage heterogeneity and variation from normal.
  
  
  RESULTS
  Healthy subjects had mean T2 values of 32.1-35.0 msec, while patients with mild and severe OA had mean T2 values of 34.4-41.0 msec. All cartilage compartments except the lateral tibia showed significant (P <.05) increases in T2 relaxation time between healthy and diseased knees; however, no significant difference was found between patients with mild and severe OA. Correlation of T2 values with clinical symptoms and cartilage morphology was found predominantly in medial compartments.
  
  
  CONCLUSIONS
  Femoral and medial tibial cartilage T2 values increase with the severity of OA.
authors.affiliation: Department of Radiology, University of California at San Francisco, 185 Berry St, Suite 350, San Francisco, CA 94107-1739, USA. tcdunn@mrsc.ucsf.edu
authors.forename: Timothy C
authors.initials: TC
authors.lastname: Dunn
authors.forename: Ying
authors.initials: Y
authors.lastname: Lu
authors.forename: Hua
authors.initials: H
authors.lastname: Jin
authors.forename: Michael D
authors.initials: MD
authors.lastname: Ries
authors.forename: Sharmila
authors.initials: S
authors.lastname: Majumdar
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002358:Cartilage, Articular / Q000473:pathology*; D005260:Female; D006801:Humans; D007089:Image Enhancement; D007091:Image Processing, Computer-Assisted; D007719:Knee Joint / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D020370:Osteoarthritis, Knee / Q000145:classification / Q000175:diagnosis*; D012016:Reference Values; D012680:Sensitivity and Specificity