The osteoarthritis initiative (OAI) magnetic resonance imaging quality assurance methods and results

To outline the osteoarthritis initiative's (OAI) magnetic resonance (MR) system quality assurance (QA) processes and present the first 3 years' results.

OAI MR QA included acquisitions evaluated manually at each of the four sites and other acquisitions assessed by an automated computer program. Key image characteristics such as signal-to-noise, contrast-to-noise, signal uniformity, T2 relaxation times, local and global geometric distortion were quantified monthly using the automated program.

Uniformly high quality, artifact-free subject images were obtained from all four OAI 3 tesla MR facilities. Over a 3-year period, key criteria for quantitative cartilage morphometry were excellent with a 190.0 mm diameter and 148.0 mm length object having reproducible diameter (0.04% RMS CV) and length (0.56% RMS CV). This resulted in spherical volume reproducibility of 0.46% RMS CV. Ghost levels were consistently <0.2%. T2 relaxation time varied longitudinally site-by-site from 2.3 to 18.8% RMS CV. All other measures of MR system stability were met except: 3.0 mm and 5.0 mm slice thicknesses were consistently larger than expected; knee coil signal uniformity and signal level varied significantly over time.

OAI MR QA results compared favorably to prior publications and identified similar technical issues for geometric measurements. The longitudinal variations measured in the OAI QA process should have minimal impact on the accuracy and reproducibility of cartilage thickness and volume quantification. This stability should enable direct comparison of baseline and follow-up images. Cross-comparison of the results from all four OAI sites reveals that the MR systems are sufficiently uniform to enable results to be combined.