title: Longitudinal in vivo reproducibility of cartilage volume and surface in osteoarthritis of the knee.
abstract: OBJECTIVE
  The aim of this study was to evaluate the longitudinal reproducibility of cartilage volume and surface area measurements in moderate osteoarthritis (OA) of the knee.
  
  
  METHODS
  We analysed 5 MRI (GE 1.5T, sagittal 3D SPGR) data sets of patients with osteoarthritis (OA) of the knee (Kellgren Lawrence grade I-II). Two scans were performed: one baseline scan and one follow-up scan 3 months later (96 +/- 10 days). For segmentation, 3D Slicer 2.5 software was used. Two segmentations were performed by two readers independently who were blinded to the scan dates. Tibial and femoral cartilage volume and surface were determined. Longitudinal and cross-sectional precision errors were calculated using the standard deviation (SD) and coefficient of variation (CV%=100x[SD/mean]) from the repeated measurements in each patient. The in vivo reproducibility was then calculated as the root mean square of these individual reproducibility errors.
  
  
  RESULTS
  The cross-sectional root mean squared coefficient of variation (RMSE-CV) was 1.2, 2.2 and 2.4% for surface area measurements (femur, medial and lateral tibia respectively) and 1.4, 1.8 and 1.3% for the corresponding cartilage volumes. Longitudinal RMSE-CV was 3.3, 3.1 and 3.7% for the surface area measurements (femur, medial and lateral tibia respectively) and 2.3, 3.3 and 2.4% for femur, medial and lateral tibia cartilage volumes.
  
  
  CONCLUSIONS
  The longitudinal in vivo reproducibility of cartilage surface and volume measurements in the knee using this segmentation method is excellent. To the best of our knowledge we measured, for the first time, the longitudinal reproducibility of cartilage volume and surface area in participants with mild to moderate OA.
authors.affiliation: Musculoskeletal Division, Department of Radiology, ASB-1, L-1, Room 003E, Harvard Medical School, Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115, USA.
authors.forename: M H
authors.initials: MH
authors.lastname: Brem
authors.forename: J
authors.initials: J
authors.lastname: Pauser
authors.forename: H
authors.initials: H
authors.lastname: Yoshioka
authors.forename: A
authors.initials: A
authors.lastname: Brenning
authors.forename: J
authors.initials: J
authors.lastname: Stratmann
authors.forename: F F
authors.initials: FF
authors.lastname: Hennig
authors.forename: R
authors.initials: R
authors.lastname: Kikinis
authors.forename: J
authors.initials: J
authors.lastname: Duryea
authors.forename: C S
authors.initials: CS
authors.lastname: Winalski
authors.forename: P
authors.initials: P
authors.lastname: Lang
mesh_terms: D000328:Adult; D000368:Aged; D001837:Body Weights and Measures / Q000379:methods*; D002358:Cartilage, Articular / Q000473:pathology*; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D007719:Knee Joint / Q000473:pathology*; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D020370:Osteoarthritis, Knee / Q000175:diagnosis*; D015203:Reproducibility of Results