U D Monu1, C D Jordan2, B L Samuelson3, B A Hargreaves4, G E Gold5, E J McWalter6. 1. Department of Radiology, Stanford University, Stanford, CA, USA; Department of Electrical Engineering, Stanford University, Stanford, CA, USA. Electronic address: udmonu@stanford.edu. 2. Department of Radiology and Biomedical Imaging, University of California San Francisco, CA, USA. Electronic address: cjordan@alumni.stanford.edu. 3. Department of Human Biology, Stanford University, Stanford, CA, USA. Electronic address: bonbon41@alumni.stanford.edu. 4. Department of Radiology, Stanford University, Stanford, CA, USA; Department of Electrical Engineering, Stanford University, Stanford, CA, USA; Department of Bioengineering, Stanford University, Stanford, CA, USA. Electronic address: bah@stanford.edu. 5. Department of Radiology, Stanford University, Stanford, CA, USA; Department of Bioengineering, Stanford University, Stanford, CA, USA; Department of Orthopaedic Surgery, Stanford University, Stanford, CA, USA. Electronic address: gold@stanford.edu. 6. Department of Mechanical Engineering, University of Saskatchewan, Saskatoon, SK, Canada. Electronic address: emily.mcwalter@usask.ca.
Abstract
PURPOSE: To identify focal lesions of elevated MRI T2 and T1ρ 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 T2 and T1ρ 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 T2 and T1ρ 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 T2 and 6.2 ± 7.1% (p = 0.063) and 8.2 ± 6.9% (p = 0.042) for T1ρ, 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 T2 and 4.4 ± 4.9% (p > 0.1) and 4.5 ± 4.6% (p > 0.1) for T1ρ, 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 T2 and T1ρ relaxation times as compared to healthy volunteers.
PURPOSE: To identify focal lesions of elevated MRI T2 and T1ρ 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 T2 and T1ρ 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 T2 and T1ρ 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 T2 and 6.2 ± 7.1% (p = 0.063) and 8.2 ± 6.9% (p = 0.042) for T1ρ, 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 T2 and 4.4 ± 4.9% (p > 0.1) and 4.5 ± 4.6% (p > 0.1) for T1ρ, 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 T2 and T1ρ relaxation times as compared to healthy volunteers.
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