Cluster analysis of quantitative MRI T 2 and T 1ρ relaxation times of cartilage identifies differences between healthy and ACL-injured individuals at 3T

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, six months and one year and six healthy volunteers at baseline, one day and one 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 six months and one 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 six months and one 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.

Imaging and T2 relaxometry of short‐T2 connective tissues in the knee using ultrashort echo‐time double‐echo steady‐state (UTEDESS)

“…Thus, magic angle could be one of the major causes of higher T 2 values in the ACL than in the PCL. Such effects with DESS T 2 have been reported earlier (61), which should be similar for UTEDESS and SE methods because the magic angle affects the actual tissue T 2 . More importantly, however, one major goal for measuring T 2 and other quantitative parameters is to assess longitudinal changes.…”

Quantitative imaging of bone–cartilage interactions in ACL-injured patients with PET–MRI

“…Furthermore, advanced quantitative MRI methods, including T 2 or T 1ρ relaxation measurement, have been associated with tissue microstructure in cartilage and meniscus and show promise for detecting early biochemical changes in OA 5 . While radiographic OA changes may take years to present, changes in cartilage matrix organization as measured by T 2 and T 1ρ relaxation times, have been observed as soon as 1 year post ACL tear and reconstruction surgery 1,6 .…”

Isotropic morphometry and multicomponent T1ρ mapping of human knee articular cartilage in vivo at 3T

“…Measuring the spin‐lattice relaxation time in the rotating frame (T 1 ρ) and spin‐spin relaxation (T 2 ) relaxation times have been studied extensively as potential noninvasive biomarkers in detecting early‐stage OA . The increase in water content and the loss of proteoglycans (PGs) in early‐stage OA results in an elevation of the T 1 ρ and T 2 relaxation times .…”

“…Measuring the spin-lattice relaxation time in the rotating frame (T 1 q) and spin-spin relaxation (T 2 ) relaxation times have been studied extensively as potential noninvasive biomarkers in detecting early-stage OA. 6,[10][11][12][13] The increase in water content and the loss of proteoglycans (PGs) in early-stage OA results in an elevation of the T 1 q and T 2 relaxation times. 6,10,14 A multicomponent model better represents the relaxation decay behavior than a monoexponential model, since the monoexponential relaxation shows the mean of relaxation in different water compartments in the cartilage, while a multicomponent model distinguishes the relaxation time of different water compartments (eg, free water, water tightly bound to PG, collagen macromolecules, etc.).…”