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BackgroundWater content is a key parameter for simulating tissue swelling and nutrient diffusion. Accurately measuring water content throughout the intervertebral disc (NP = nucleus pulposus; AF = annulus fibrosus) is important for developing patient-specific models. Water content is measured using destructive techniques, Quantitative MRI has been used to estimate water content and detect early degeneration, but it is dependent on scan parameters, concentration of free water molecules, and fiber architecture.PurposeTo directly measure disc-tissue water content using quantitative MRI and compare MRI-based measurements with biochemical assays, and to quantify changes in disc geometry due to compression.Study typeBasic science, controlled.SpecimenTwenty bone-disc-bone motion segments from skeletally mature bovines.Field strength/sequence7T/3D fast low angle shot (FLASH) pulse sequence and a T2 rapid imaging with refocused echoes (RARE) sequence.AssessmentDisc volumes, NP and AF volumetric water content, and T2 relaxation times were measured through MRI; NP and AF tissue gravimetric water content, mass density, and glycosaminoglycan content were measured through a biochemical assay.Statistical testsCorrelations between MRI-based measurement and biochemical composition were evaluated using Pearson's linear regression.ResultsMechanical dehydration resulted in a decrease in disc volume by up to 20% and a decrease in disc height by up to 35%. Direct water content measurements for the NP was achieved by normalizing MRI-based spin density by NP mass density (1.10 ± 0.03 g/cm3 ). However, the same approach underestimated water content in the AF by ~10%, which may be due to a higher concentration of collagen fibers and bound water molecules.Data conclusionSpin density or spin density normalized by mass density to estimate NP and AF water content was more accurate than correlations between water content and relaxation times. Mechanical dehydration decreased disc volume and disc height, and increased maximum cross-sectional area.Level of evidenceTECHNICAL EFFICACY STAGE:   J. Magn. Reson. Imaging 2020;52:1152-1162.

ObjectiveTo evaluate the degree of knee fat pad abnormalities after acute anterior cruciate ligament (ACL) tear via magnetic resonance fat pad scoring and to assess cross-sectionally its association with synovial fluid biomarkers and with early cartilage damage as quantified via T1ρ and T2 relaxation time measurements.Design26 patients with acute ACL tears underwent 3T MR scanning of the injured knee prior to ACL reconstruction. The presence and degree of abnormalities of the infrapatellar (IPFP) and the suprapatellar (SPFP) fat pads were scored on MR images along with grading of effusion-synovitis and synovial proliferations. Knee cartilage composition was assessed by 3T MR T1ρ and T2 mapping in six knee compartments. We quantified concentrations of 20 biomarkers in synovial fluid aspirated at the time of ACL reconstruction. Spearman rank partial correlations with adjustments for age and gender were employed to evaluate correlations of MR, particularly cartilage composition and fat pad abnormalities, and biomarker data.ResultsThe degree of IPFP abnormality correlated positively with the synovial levels of the inflammatory cytokine markers IFN-γ (ρpartial = 0.64, 95% CI (0.26-0.85)), IL-10 (ρpartial = 0.47, 95% CI (0.04-0.75)), IL-6 (ρpartial = 0.56, 95% CI (0.16-0.81)), IL-8 (ρpartial = 0.49, 95% CI (0.06-0.76)), TNF-α (ρpartial = 0.55, 95% CI (0.14-0.80)) and of the chondrodestructive markers MMP-1 and -3 (MMP-1: ρpartial = 0.57, 95% CI (0.17-0.81); MMP-3: ρpartial = 0.60, 95% CI (0.21-0.83)). IPFP abnormalities were significantly associated with higher T1ρ and T2 values in the trochlear cartilage (T1ρ: ρpartial = 0.55, 95% CI (0.15-0.80); T2: ρpartial = 0.58, 95% CI (0.18-0.81)) and with higher T2 values in the medial femoral, medial tibial as well as in patellar cartilage (0.45 ≤ ρpartial ≤ 0.59). Correlations between SPFP abnormalities and synovial markers were not significant except for IL-6 (ρpartial = 0.57, 95% CI (0.17-0.81)).ConclusionsThis exploratory study suggests that acute ACL rupture can be associated with damage to knee tissues such as the inferior fat pad of the knee. Such fat pad injury could be partially responsible for the apparent post-injury pro-inflammatory response noted in ACL-injured individuals. However, future longitudinal studies are needed to link ACL-rupture associated fat pad injury with important patient outcomes such as the development of posttraumatic osteoarthritis.

Background: Magnetic resonance fingerprinting (MRF) techniques have been recently described for simultaneous multiparameter cartilage mapping of the knee although investigation of their ability to detect early cartilage degeneration remains limited. Purpose: To investigate age‐dependent changes in knee cartilage T1, T2, and T1p relaxation times measured using a three‐dimensional (3D) MRF sequence in healthy volunteers. Study Type: Prospective. Subjects: The study group consisted of 24 healthy asymptomatic human volunteers (15 males with mean age 34.9 ± 14.4 years and 9 females with mean age 44.5 ± 13.1 years). Field Strength/Sequence: A 3.0 T gradient‐echo‐based 3D‐MRF sequence was used to simultaneously create proton density‐weighted images and T1, T2, and T1p maps of knee cartilage. Assessment: Mean global cartilage and regional cartilage (lateral femur, lateral tibia, medial femur, medial tibia, and patella) T1, T2, and T1ρ relaxation times of the knee were measured. Statistical Tests: Kruskal–Wallis tests were used to compared cartilage T1, T2, and T1ρ relaxation times between different age groups, while Spearman correlation coefficients was used to determine the association between age and cartilage T1, T2, and T1ρ relaxation times. The value of P < 0.05 was considered statistically significant. Results: Higher age groups showed higher global and regional cartilage T1, T2, and T1ρ. There was a significant difference between age groups in global cartilage T2 and T1ρ but no significant difference (P = 0.13) in global cartilage T1. Significant difference was also present between age groups in cartilage T2 and T1ρ for medial femur cartilage and medial tibia cartilage. There were significant moderate correlations between age and T2 and T1ρ for global cartilage (R2 = 0.63–0.64), medial femur cartilage (R2 = 0.50–0.56), and medial tibia cartilage (R2 = 0.54–0.66). Conclusion: Cartilage T2 and T1p relaxation times simultaneously measured using a 3D‐MRF sequence in healthy volunteers showed age‐dependent changes in knee cartilage, primarily within the medial compartment. [ABSTRACT FROM AUTHOR]

BackgroundMapping of T1ρ relaxation time is a quantitative magnetic resonance (MR) method and is frequently used for analyzing microstructural and compositional changes in cartilage tissues. However, there is still a lack of study investigating the link between T1ρ relaxation time and a feasible constitutive relation of cartilage which can be used to model complicated mechanical behaviors of cartilage accurately and properly.MethodsThree-dimensional finite element (FE) models of ten in vitro human tibial cartilage samples were reconstructed such that each element was assigned by material-level parameters, which were determined by a corresponding T1ρ value from MR maps. A T1ρ-based fibril-reinforced poroviscoelastic (FRPE) constitutive relation for human cartilage was developed through an inverse FE optimization technique between the experimental and simulated indentations.ResultsA two-parameter exponential relationship was obtained between the T1ρ and the volume fraction of the hydrated solid matrix in the T1ρ-based FRPE constitutive relation. Compared with the common FRPE constitutive relation (i.e., without T1ρ), the T1ρ-based FRPE constitutive relation indicated similar indentation depth results but revealed some different local changes of the stress distribution in cartilages.ConclusionsOur results suggested that the T1ρ-based FRPE constitutive relation may improve the detection of changes in the heterogeneous, anisotropic, and nonlinear mechanical properties of human cartilage tissues associated with joint pathologies such as osteoarthritis (OA). Incorporating T1ρ relaxation time will provide a more precise assessment of human cartilage based on the individual in vivo MR quantification.

Background: Magnetic resonance fingerprinting (MRF) techniques have been recently described for simultaneous multiparameter cartilage mapping of the knee although investigation of their ability to detect early cartilage degeneration remains limited., Purpose: To investigate age-dependent changes in knee cartilage T 1 , T 2 , and T 1p relaxation times measured using a three-dimensional (3D) MRF sequence in healthy volunteers., Study Type: Prospective., Subjects: The study group consisted of 24 healthy asymptomatic human volunteers (15 males with mean age 34.9 ± 14.4 years and 9 females with mean age 44.5 ± 13.1 years)., Field Strength/sequence: A 3.0 T gradient-echo-based 3D-MRF sequence was used to simultaneously create proton density-weighted images and T 1 , T 2 , and T 1p maps of knee cartilage., Assessment: Mean global cartilage and regional cartilage (lateral femur, lateral tibia, medial femur, medial tibia, and patella) T 1 , T 2 , and T 1ρ relaxation times of the knee were measured., Statistical Tests: Kruskal-Wallis tests were used to compared cartilage T 1 , T 2 , and T 1ρ relaxation times between different age groups, while Spearman correlation coefficients was used to determine the association between age and cartilage T 1 , T 2 , and T 1ρ relaxation times. The value of P < 0.05 was considered statistically significant., Results: Higher age groups showed higher global and regional cartilage T 1 , T 2 , and T 1ρ . There was a significant difference between age groups in global cartilage T 2 and T 1ρ but no significant difference (P = 0.13) in global cartilage T 1. Significant difference was also present between age groups in cartilage T 2 and T 1ρ for medial femur cartilage and medial tibia cartilage. There were significant moderate correlations between age and T 2 and T 1ρ for global cartilage (R 2  = 0.63-0.64), medial femur cartilage (R 2  = 0.50-0.56), and medial tibia cartilage (R 2  = 0.54-0.66)., Conclusion: Cartilage T 2 and T 1p relaxation times simultaneously measured using a 3D-MRF sequence in healthy volunteers showed age-dependent changes in knee cartilage, primarily within the medial compartment., (© 2022 International Society for Magnetic Resonance in Medicine.)