title: The Osteoarthritis Initiative (OAI) magnetic resonance imaging quality assurance update.
abstract: OBJECTIVE
  Longitudinal quantitative evaluation of cartilage disease requires reproducible measurements over time. We report 8 years of quality assurance (QA) metrics for quantitative magnetic resonance (MR) knee analyses from the Osteoarthritis Initiative (OAI) and show the impact of MR system, phantom, and acquisition protocol changes.
  
  
  METHODS
  Key 3T MR QA metrics, including signal-to-noise, signal uniformity, T2 relaxation times, and geometric distortion, were quantified monthly on two different phantoms using an automated program.
  
  
  RESULTS
  Over 8 years, phantom measurements showed root-mean-square coefficient-of-variation reproducibility of <0.25% (190.0 mm diameter) and <0.20% (148.0 mm length), resulting in spherical volume reproducibility of <0.35%. T2 relaxation time reproducibility varied from 1.5% to 5.3%; seasonal fluctuations were observed at two sites. All other QA goals were met except: slice thicknesses were consistently larger than nominal on turbo spin echo images; knee coil signal uniformity and signal level varied significantly over time.
  
  
  CONCLUSIONS
  The longitudinal variations for a spherical volume should have minimal impact on the accuracy and reproducibility of cartilage volume and thickness measurements as they are an order of magnitude smaller than reported for either unpaired or paired (repositioning and reanalysis) precision errors. This stability should enable direct comparison of baseline and follow-up images. Cross-comparison of the geometric results from all four OAI sites reveal that the MR systems do not statistically differ and enable results to be pooled. MR QA results identified similar technical issues as previously published. Geometric accuracy stability should have the greatest impact on quantitative analysis of longitudinal change in cartilage volume and thickness precision.
authors.affiliation: Imaging Institute, Cleveland Clinic Foundation, Cleveland, OH 44116, USA. schneie1@ccf.org
authors.forename: E
authors.initials: E
authors.lastname: Schneider
authors.forename: M
authors.initials: M
authors.lastname: Nessaiver
mesh_terms: D002358:Cartilage, Articular / Q000000981:diagnostic imaging / Q000473:pathology*; D006801:Humans; D021621:Imaging, Three-Dimensional; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods / Q000592:standards*; D015337:Multicenter Studies as Topic; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000473:pathology*; D019047:Phantoms, Imaging; D011785:Quality Assurance, Health Care; D011859:Radiography; D015203:Reproducibility of Results; D014481:United States