Cluster analysis of quantitative MRI T2 and T1ρ relaxation times of cartilage identifies differences between healthy and ACL-injured individuals at 3T

Purpose: To identify focal lesions of elevated MRI T-2 and T-1 rho relaxation times in articular cartilage of an ACL-injured group using a novel cluster analysis technique. Materials and methods: Eighteen ACL-injured patients underwent 3T MRI T-2 and T-1 rho relaxometry at baseline, 6 months and 1 year and six healthy volunteers at baseline, 1 day and 1 year. Clusters of contiguous pixels above or below T-2 and T-1 rho intensity and area thresholds were identified on a projection map of the 3D femoral cartilage surface. The total area of femoral cartilage plate covered by clusters (%CA) was split into areas above (%CA+) and below (%CA-) the thresholds and the differences in %CA(+ or -) over time in the ACL-injured group were determined using the Wilcoxon signed rank test. Results: %CA+ was greater in the ACL-injured patients than the healthy volunteers at 6 months and 1 year with average %CA+ of 5.2 +/- 4.0% (p = 0.0054) and 6.6 +/- 3.7% (p = 0.0041) for T-2 and 6.2 +/- 7.1% (p = 0.063) and 8.2 +/- 6.9% (p = 0.042) for T-1 rho, respectively. %CA- at 6 months and 1 year was 3.0 +/- 1.8% (p > 0.1) and 5.9 +/- 5.0% (p > 0.1) for T-2 and 4.4 +/- 4.9% (p > 0.1) and 4.5 +/- 4.6% (p > 0.1) for T-1 rho, respectively. Conclusion: With the proposed cluster analysis technique, we have quantified cartilage lesion coverage and demonstrated that the ACL-injured group had greater areas of elevated T-2 and T-1 rho relaxation times as compared to healthy volunteers. (C) 2016 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.