Repeatability of focal changes in knee cartilage T2 relaxation times with load and time

The purpose of this study is to assess the repeatability of focal changes in T 2 relaxation time of knee articular cartilage with load and over time. A short-term repeatability study was conducted in five healthy participants. Images were acquired of the knee in an unloaded position and in loaded flexion with a custom, quantitative Double Echo Steady State (qDESS) MRI sequence on a 3T scanner. The protocol was carried out three times within a one-week period. T 2 relaxation maps of the tibial and femoral articular cartilage were created and focal areas of change were identified using a cluster-based analysis approach; the outcome measure was defined as the percentage area covered by a cluster of pixels that change with load or over time. Average T 2 relaxation time within anatomical regions was also calculated. Repeatability of the cluster-based and regional approach was described as the root mean square standard deviation (SDrms) of the trials. The SDrms of the percentage area of the entire cartilage surface covered by clusters when the knees were loaded was less than 9.5%. The repeatability of the percentage area of the entire cartilage surface covered by clusters over time was less than 4.5% for the unloaded knees and 7.4% for the loaded knees. For the regional analysis, the average SDrms of the entire plate was less than 3.0 ms. Cluster analysis provides important information on focal changes in cartilage with the application of load and over time, but at the cost of lost repeatability compared to regional approaches.