OBJECTIVE The purpose of this study was to measure and compare the relaxation times of musculoskeletal tissues at 3.0T and 7.0T, and to use these measurements to select appropriate parameters for musculoskeletal protocols at 7.0T. MATERIALS AND METHODS We measured the T1 and T2 relaxation times of cartilage, muscle, synovial fluid, bone marrow and subcutaneous fat at both 3.0T and 7.0T in the knees of five healthy volunteers. The T1 relaxation times were measured using a spin-echo inversion recovery sequence with six inversion times. The T2 relaxation times were measured using a spin-echo sequence with seven echo times. The accuracy of both the T1 and T2 measurement techniques was verified in phantoms at both magnetic field strengths. We used the measured relaxation times to help design 7.0T musculoskeletal protocols that preserve the favorable contrast characteristics of our 3.0T protocols, while achieving significantly higher resolution at higher SNR efficiency. RESULTS The T1 relaxation times in all tissues at 7.0T were consistently higher than those measured at 3.0T, while the T2 relaxation times at 7.0T were consistently lower than those measured at 3.0T. The measured relaxation times were used to help develop high resolution 7.0T protocols that had similar fluid-to-cartilage contrast to that of the standard clinical 3.0T protocols for the following sequences: proton-density-weighted fast spin-echo (FSE), T2-weighted FSE, and 3D-FSE-Cube. CONCLUSION The T1 and T2 changes were within the expected ranges. Parameters for musculoskeletal protocols at 7.0T can be optimized based on these values, yielding improved resolution in musculoskeletal imaging with similar contrast to that of standard 3.0T clinical protocols.

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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.