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.

OBJECTIVE To measure the variability of T1ρ relaxation times using CubeQuant, T2 relaxation times using quantitative double echo in steady state (DESS), and normalized sodium signals using 3D cones sodium MRI of knee cartilage in vivo at 3T. DESIGN Eight healthy subjects were scanned at 3T at baseline, one day, five months, and one year. Ten regions of interest (ROIs) of knee cartilage were segmented in the medial and lateral compartments of each subject’s knee. T1ρ and T2 relaxation times and normalized sodium signals were measured and the root-mean-square coefficient of variation (CVRMS) was calculated. Intra-subject variability was measured over short, moderate and long-term, as well as intra-observer and inter-observer variability. RESULTS The average intra-subject CVRMS measurements over short, moderate, and long-term time periods were 4.6%, 6.1%, and 6.0% for the T1ρ measurements, 6.4%, 9.3%, and 10.7% for the T2 measurements and 11.3%, 11.6%, and 12.9% for the sodium measurements, respectively. The average CVRMS measurements for intra-observer and inter-observer segmentation were 3.8% and 5.7% for the T1ρ measurements, 4.7% and 6.7% for the T2 measurements, and 8.1% and 11.4% for the sodium measurements, respectively. CONCLUSIONS These CVRMS measurements are substantially lower than previously measured changes expected in patients with advanced osteoarthritis compared to healthy volunteers, suggesting that CubeQuant T1ρ, quantitative DESS T2 and 3D cones sodium measurements are sufficiently sensitive for in vivo cartilage studies.

Objective: To investigate changes in bone metabolism by PET, as well as spatial relationships between bone metabolism and MRI quantitative markers of early cartilage degradation, in ACL-reconstructed knees. Design: Both knees of 15 participants with unilateral reconstructed ACL tears and unaffected contralateral knees were scanned using a simultaneous 3.0T PET-MRI system following injection of 18F-sodium fluoride(18F-NaF). The maximum pixel standardized uptake value(SUVmax) in the subchondral bone and the average T2 relaxation time in cartilage were measured in each knee in 8 knee compartments. We tested differences in SUVmax and cartilage T2 relaxation times between the ACL-injured knee and the contralateral control knee as well as spatial relationships between these bone and cartilage changes. Results: Significantly increased subchondral bone 18F-NaF SUVmax and cartilage T2 times were observed in the ACL-reconstructed knees (median[inter-quartile-range(IQR)]:5.0[5.8],36.8[3.6]ms) compared to the contralateral knees (median[IQR]:1.9[1.4],34.4[3.8]ms). A spatial relationship between the two markers was also seen. Using the contralateral knee as a control, we observed a significant correlation of r= 0.59 between the difference in subchondral bone SUVmax (between injured and contralateral knees) and the adjacent cartilage T2 (between the two knees)[p<0.001], with a slope of 0.49ms/a.u. This correlation and slope were higher in deep layers (r=0.73,slope=0.60ms/a.u.) of cartilage compared to superficial layers (r=0.40,slope=0.43ms/a.u.). Conclusions: 18F-NaF PET-MR imaging enables detection of increased subchondral bone metabolism in ACL-reconstructed knees and may serve as an important marker of early OA progression. Spatial relationships observed between early OA changes across bone and cartilage support the need to study whole-joint disease mechanisms in OA.

A bilateral coil-array setup can image both knees simultaneously in similar scan times as conventional unilateral knee scans, with comparable image quality and quantitative accuracy. This has the potential to improve the value of MRI knee evaluations. Magn Reson Med 80:529-537, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Background: Previous studies have shown that runners demonstrate elevated T2 and T1ρ values on magnetic resonance imaging (MRI) after running a marathon, with the greatest changes in the patellofemoral and medial compartment, which can persist after 3 months of reduced activity. Additionally, marathon running has been shown to increase serum inflammatory markers. Hyaluronic acid (HA) purportedly improves viscoelasticity of synovial fluid, serving as a lubricant while also having chondroprotective and anti-inflammatory effects. Purpose/Hypothesis: The purpose was to investigate whether intra-articular HA injection can protect articular cartilage from injury attributed to marathon running. The hypothesis was that the addition of intra-articular HA 1 week before running a marathon would reduce the magnitude of early cartilage breakdown measured by MRI. Study Design: Randomized controlled trial; Level of evidence, 2. Methods: After institutional review board approval, 20 runners were randomized into receiving an intra-articular injection of HA or normal saline (NS) 1 week before running a marathon. Exclusionary criteria included any prior knee injury or surgery and having run >3 prior marathons. Baseline 3-T knee MRI was obtained within 48 hours before the marathon (approximately 5 days after injection). Follow-up 3-T MRI scans of the same knee were obtained 48 to 72 hours and 3 months after the marathon. The T2 and T1ρ relaxation times of articular cartilage were measured in 8 locations—the medial and lateral compartments (including 2 areas of each femoral condyle) and the patellofemoral joint. The statistical analysis compared changes in T2 and T1ρ relaxation times (ms) from baseline to immediate and 3-month postmarathon scans between the HA and NS groups with repeated measures analysis of variance. Results: Fifteen runners completed the study: 6 women and 2 men in the HA group (mean age, 31 years; range, 23-50 years) and 6 women and 1 man in the NS group (mean age, 27 years; range, 20-49 years). There were no gross morphologic MRI changes after running the marathon. Postmarathon studies revealed no statistically significant changes between the HA and NS groups in all articular cartilage areas of the knee on both T2 and T1ρ relaxation times. Conclusion: Increased T2 and T1ρ relaxation times have been observed in marathon runners, suggesting early cartilage injury. The addition of intra-articular HA did not significantly affect relaxation times in all areas of the knee when compared with an NS control.