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Metabolic and structural changes in cartilage tissue are thought to be at the root of degenerative joint disease. We identify here the NMR resonances in bovine patellar cartilage tissue by static and high-resolution magic angle spinning (HRMAS) NMR spectroscopy, (1)H-(13)C heteronuclear single-quantum correlation (HSQC) spectroscopy, total correlation spectroscopy (TOCSY), and saturation transfer experiments. Some differences between the patellar cartilage samples studied here and earlier nasal cartilage and intervertebrate disc studies were found. In addition, we show assignments downfield of the water signal, which also includes the assignment of amide and hydroxy protons on the basis of their exchangeability with water. These results will allow an identification of spectroscopic markers of cartilage degradation using techniques such as chemical exchange saturation transfer imaging., (Copyright (c) 2007 John Wiley & Sons, Ltd.)

Low‐field strength scanners present an opportunity for more inclusive imaging exams and bring several challenges including lower signal‐to‐noise ratio (SNR) and longer scan times. Magnetic resonance fingerprinting (MRF) is a rapid quantitative multiparametric method that can enable multiple quantitative maps simultaneously. To demonstrate the feasibility of an MRF sequence for knee cartilage evaluation in a 0.55T system we performed repeatability and accuracy experiments with agar‐gel phantoms. Additionally, five healthy volunteers (age 32 ± 4 years old, 2 females) were scanned at 3T and 0.55T. The MRI acquisition protocols include a stack‐of‐stars T1ρ‐enabled MRF sequence, a VIBE sequence with variable flip angles (VFA) for T1 mapping, and fat‐suppressed turbo flash (TFL) sequences for T2 and T1ρ mappings. Double‐Echo steady‐state (DESS) sequence was also used for cartilage segmentation. Acquisitions were performed at two different field strengths, 0.55T and 3T, with the same sequences but protocols were slightly different to accommodate differences in signal‐to‐noise ratio and relaxation times. Cartilage segmentation was done using five compartments. T1, T2, and T1ρ values were measured in the knee cartilage using both MRF and conventional relaxometry sequences. The MRF sequence demonstrated excellent repeatability in a test–retest experiment with model agar‐gel phantoms, as demonstrated with correlation and Bland–Altman plots. Underestimation of T1 values was observed on both field strengths, with the average global difference between reference values and the MRF being 151 ms at 0.55T and 337 ms at 3T. At 0.55T, MRF measurements presented significant biases but strong correlations with the reference measurements. Although a larger error was present in T1 measurements, MRF measurements trended similarly to the conventional measurements for human subjects and model agar‐gel phantoms. [ABSTRACT FROM AUTHOR]

Purpose: To compare the performance of a learned magnetization‐prepared gradient echo (L‐MPGRE) sequence against a commonly used sequence for 3D T2 and T1ρ mapping of the knee joint, the magnetization‐prepared angle‐modulated partitioned k‐space spoiled gradient echo snapshots (MAPSS), on bi‐exponential (BE), stretched‐exponential (SE), and mono‐exponential (ME) relaxation models. Methods: We used a combined differentiable and non‐differentiable optimization to learn pulse sequence structure and its parameters for 3D T2 and T1ρ mapping of the knee joint using ME, SE, and BE models. The learned pulse sequence framework was used to improve quantitative accuracy and SNR and to reduce filtering effects. We compare the measured multi‐compartment values between the two sequences (n = 8), and their repeatability (n = 4) in healthy volunteers (n = 12 total). Results: The voxel‐wise median absolute percentage difference (MAPD) between the T2 and T1ρ maps obtained with each sequence was 18.6% and 19.9%, respectively. The T2 and T1ρ repeatability tests showed a MAPD of 18.5% and 19.1% for MAPSS, and 16.8% and 15.5% for L‐MPGRE. Bland–Altman region of interest (ROI)‐wise analysis shows that bias is small, close to −1.5%, and the coefficient of variation is around 5.5% when comparing ROIs from both sequences. Conclusion: The L‐MPGRE sequences can be used as a replacement for MAPSS for T2 and T1ρ mapping in the knee cartilage with advantages, achieving similar accuracy and 15% better repeatability in only half of its scan time. [ABSTRACT FROM AUTHOR]

Background: Three‐dimensional MR fingerprinting (3D‐MRF) techniques have been recently described for simultaneous multiparametric mapping of knee cartilage. However, investigation of repeatability remains limited. Purpose: To assess the intra‐day and inter‐day repeatabilities of knee cartilage T1, T2, and T1ρ maps using a 3D‐MRF sequence for simultaneous measurement. Study Type: Prospective. Subjects: Fourteen healthy subjects (35.4 ± 9.3 years, eight males), scanned on Day 1 and Day 7. Field Strength/Sequence: 3 T/3D‐MRF, T1, T2, and T1ρ maps. Assessment: The acquisition of 3D‐MRF cartilage (simultaneous acquisition of T1, T2, and T1ρ maps) were acquired using a dictionary pattern‐matching approach. Conventional cartilage T1, T2, and T1ρ maps were acquired using variable flip angles and a modified 3D‐Turbo‐Flash sequence with different echo and spin‐lock times, respectively, and were fitted using mono‐exponential models. Each sequence was acquired on Day 1 and Day 7 with two scans on each day. Statistical Tests: The mean and SD for cartilage T1, T2, and T1ρ were calculated in five manually segmented regions of interest (ROIs), including lateral femur, lateral tibia, medial femur, medial tibia, and patella cartilages. Intra‐subject and inter‐subject repeatabilities were assessed using coefficient of variation (CV) and intra‐class correlation coefficient (ICC), respectively, on the same day and among different days. Regression and Bland–Altman analysis were performed to compare maps between the conventional and 3D‐MRF sequences. Results: The CV in all ROIs was lower than 7.4%, 8.4%, and 7.5% and the ICC was higher than 0.56, 0.51, and 0.52 for cartilage T1, T2, and T1ρ, respectively. The MRF results had a good agreement with the conventional methods with a linear regression slope >0.61 and R2 > 0.59. Conclusion: The 3D‐MRF sequence had high intra‐subject and inter‐subject repeatabilities for simultaneously measuring knee cartilage T1, T2, and T1ρ with good agreement with conventional sequences. Evidence Level: 1 Technical Efficacy: Stage 1 [ABSTRACT FROM AUTHOR]

Osteoarthritis (OA) is a widely occurring degenerative joint disease that is severely debilitating and causes significant socioeconomic burdens to society. Magnetic resonance imaging (MRI) is the preferred imaging modality for the morphological evaluation of cartilage due to its excellent soft tissue contrast and high spatial resolution. However, its utilization typically involves subjective qualitative assessment of cartilage. Compositional MRI, which refers to the quantitative characterization of cartilage using a variety of MRI methods, can provide important information regarding underlying compositional and ultrastructural changes that occur during early OA. Cartilage compositional MRI could serve as early imaging biomarkers for the objective evaluation of cartilage and help drive diagnostics, disease characterization, and response to novel therapies. This review will summarize current and ongoing state‐of‐the‐art cartilage compositional MRI techniques and highlight emerging methods for cartilage compositional MRI including MR fingerprinting, compressed sensing, multiexponential relaxometry, improved and robust radio‐frequency pulse sequences, and deep learning‐based acquisition, reconstruction, and segmentation. The review will also briefly discuss the current challenges and future directions for adopting these emerging cartilage compositional MRI techniques for use in clinical practice and translational OA research studies. Evidence Level: 2 Technical Efficacy: Stage 2. [ABSTRACT FROM AUTHOR]

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]

Two optimization criteria based on Cramér-Rao Bounds are compared between each other and with non-optimized schedules for T1ρ mapping using synthetic data, model phantoms, and in-vivo knee cartilage. The curve fitting is done on complex-valued data using an iterative Nonlinear Least Squares (NLS) approach. The optimization criteria are compared based on the Mean Normalized Absolute Error (MNAE) and variance of the estimated parameters. The optimized spin-lock time (TSL) schedules provided improved results over the non-optimized schedules for all cases that were tested. The simulations showed that optimized schedules can reach the same precision and reduce acquisition times by 16.5 min (42%) for the bi-exponential model, and 6.6 min (22%) for the stretched-exponential model. In the model phantoms experiments, the bi-exponential MNAE was reduced from 0.47 to 0.36, while stretched-exponential from 0.28 to 0.20 with a Modified Cramér-Rao Lower Bound (MCRLB). In-vivo knee cartilage experiments show a reduction in bi-exponential MNAE from 0.47 to 0.31, and stretched-exponential from 0.047 to 0.039. The optimized spin-lock times criteria reduced the error in all cases, being more significant in the synthetic data and model phantoms. The optimized TSL schedules can be either used to improve the quality of parameter maps or reduce scan time. [ABSTRACT FROM AUTHOR]

Purpose: To compare different optimization approaches for choosing the spin‐lock times (TSLs), in spin‐lattice relaxation time in the rotating frame (T1ρ) mapping. Methods: Optimization criteria for TSLs based on Cramér‐Rao lower bounds (CRLB) are compared with matched sampling‐fitting (MSF) approaches for T1ρ mapping on synthetic data, model phantoms, and knee cartilage. The MSF approaches are optimized using robust methods for noisy cost functions. The MSF approaches assume that optimal TSLs depend on the chosen fitting method. An iterative non‐linear least squares (NLS) and artificial neural networks (ANN) are tested as two possible T1ρ fitting methods for MSF approaches. Results: All optimized criteria were better than non‐optimized ones. However, we observe that a modified CRLB and an MSF based on the mean of the normalized absolute error (MNAE) were more robust optimization approaches, performing well in all tested cases. The optimized TSLs obtained the best performance with synthetic data (3.5–8.0% error), model phantoms (1.5–2.8% error), and healthy volunteers (7.7–21.1% error), showing stable and improved quality results, comparing to non‐optimized approaches (4.2–13.3% error on synthetic data, 2.1–6.2% error on model phantoms, 9.8–27.8% error on healthy volunteers). Conclusion: A modified CRLB and the MSF based on MNAE are robust optimization approaches for choosing TSLs in T1ρ mapping. All optimized criteria allowed good results even using rapid scans with two TSLs when a complex‐valued fitting is done with iterative NLS or ANN. [ABSTRACT FROM AUTHOR]

Purpose: To implement a novel technique for simultaneous, quantitative multiparametric mapping of the knee articular cartilage. Methods: A novel MR fingerprinting pulse sequence is proposed and implemented for simultaneous measurements of proton density, T1, T2, and T1ρ relaxation times at 3T. The repeatability and reproducibility of the proposed technique were assessed in model phantoms. Institutional review board‐approved MR fingerprinting imaging sequence was performed on healthy volunteers and patients with mild knee osteoarthritis. The Wilcoxon test was used to compare healthy controls and patients. The intra‐ and intersubject repeatability were assessed with coefficient of variation and the RMS coefficient of variation, respectively Results: The Bland‐Altman plots demonstrated an average difference of 4.67 ms, −0.09 ms, and 0.05 ms between 2 scans in the same scanner; and 9.68 ms, 0.29 ms, and −0.72 ms between the scans acquired on 2 different scanners for T1, T2, and T1ρ, respectively. The in vivo knee study showed excellent repeatability with RMS coefficient of variation less than 3%, 6%, and 5% for T1, T2, and T1ρ, respectively. The Wilcoxon test showed a significant difference between control and mild osteoarthritis patients for T1 (P =.04), T2 (P =.01), and T1ρ (P =.02) relaxation time in medial tibial cartilage, as well as for T2 relaxation time (P =.02) in medial femoral cartilage. Conclusion: The proposed MRF sequence is fast and can simultaneously measure the T1, T2, T1ρ, and B1+ maps in a single scan. It is able to discriminate between mild osteoarthritis patients and healthy volunteers. [ABSTRACT FROM AUTHOR]

Purpose: To use golden‐angle radial sampling and compressed sensing (CS) for accelerating mono‐ and biexponential 3D spin‐lattice relaxation time in the rotating frame (T1ρ) mapping of knee cartilage. Methods: Golden‐angle radial stack‐of‐stars and Cartesian 3D‐T1ρ‐weighted knee cartilage datasets (n = 12) were retrospectively undersampled by acceleration factors (AFs) 2‐10. CS‐based reconstruction using 8 different sparsifying transforms were compared for mono‐ and biexponential T1ρ‐mapping of knee cartilage, including spatio‐temporal finite differences, wavelets, dictionary from principal component analysis, and exponential decay models, and also low rank and low rank plus sparse models (L+S). Complex‐valued fitting was used and Marchenko‐Pastur principal component analysis filtering also tested. Results: Most CS methods performed well for an AF of 2, with relative median normalized absolute deviation below 10% for monoexponential and biexponential mapping. For monoexponential mapping, radial sampling obtained a median normalized absolute deviation below 10% up to AF of 10, while Cartesian obtained this level of error only up to AF of 4. Radial sampling was also better with biexponential T1ρ mapping, with median normalized absolute deviation below 10% up to AF of 6. Conclusion: Golden‐angle radial acquisitions combined with CS outperformed Cartesian acquisitions for 3D‐T1ρ mapping of knee cartilage, being it is a good alternative to Cartesian sampling for reducing scan time and/or improving image and mapping quality. The methods exponential decay models, spatio‐temporal finite differences, and low rank obtained the best results for radial sampling patterns. [ABSTRACT FROM AUTHOR]

Background: Quantification of dynamic biomechanical strain in articular cartilage in vivo; in situ using noninvasive MRI techniques is desirable and may potentially be used to assess joint pathology.Purpose: To demonstrate the use of static mechanical loading and continuous 3D-MRI acquisition of the human knee joint in vivo to measure the strain in the tibiofemoral articular cartilage.Study Type: Prospective.Subjects: Five healthy human volunteers (four women, one man; age 25.6 ± 1.7) underwent MRI at rest, under static mechanical loading condition, and during recovery.Field Strength/sequence: A field strength of 3T was used. The sequence used was 3D-continuous golden angle radial sparse parallel (GRASP) MRI and compressed sensing (CS) reconstruction.Assessment: Tibiofemoral cartilage deformation maps under loading and during recovery were calculated using an optical flow algorithm. The corresponding Lagrangian strain was calculated in the articular cartilage.Statistical Tests: Range of displacement and strain in each subject, and the resulting mean and standard deviation, were calculated.Results: During the loading condition, the cartilage displacement in the direction of loading ranged from a minimum of -673.6 ± 121.9 μm to a maximum of 726.5 ± 169.5 μm. Corresponding strain ranged from a minimum of -7.0 ± 4.2% to a maximum of 5.4 ± 1.6%. During the recovery condition, the cartilage displacement in the same direction reduced to a minimum of -613.0 ± 129.5 μm and a maximum of 555.7 ± 311.4 μm. The corresponding strain range reduced to a minimum of -1.6 ± 7.5% to a maximum of 4.2 ± 2.6%.Data Conclusion: This study shows the feasibility of using static mechanical loading with continuous GRASP-MRI acquisition to measure the strain in the articular cartilage. By measuring strain during the loading and recovery phases, dynamic strain information in the articular cartilage might be able to be investigated.Level Of Evidence: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2020;51:426-434. [ABSTRACT FROM AUTHOR]

Objectives: To evaluate the potential of sodium MRI to detect changes over time of apparent sodium concentration (ASC) in articular cartilage in patients with knee osteoarthritis (OA).Methods: The cartilage of 12 patients with knee OA were scanned twice over a period of approximately 16 months with two sodium MRI sequences at 7 T: without fluid suppression (radial 3D) and with fluid suppression by adiabatic inversion recovery (IR). Changes between baseline and follow-up of mean and standard deviation of ASC (in mM), and their rate of change (in mM/day), were measured in the patellar, femorotibial medial and lateral cartilage regions for each subject. A matched-pair Wilcoxon signed rank test was used to assess significance of the changes.Results: Changes in mean and in standard deviation of ASC, and in their respective rate of change over time, were only statistically different when data was acquired with the fluid-suppressed sequence. A significant decrease (p = 0.001) of approximately 70 mM in mean ASC was measured between the two IR scans.Conclusion: Quantitative sodium MRI with fluid suppression by adiabatic IR at 7 T has the potential to detect a decrease of ASC over time in articular cartilage of patients with knee osteoarthritis.Key Points: • Sodium MRI can detect apparent sodium concentration (ASC) in cartilage • Longitudinal study: sodium MRI can detect changes in ASC over time • Potential for follow-up studies of cartilage degradation in knee osteoarthritis. [ABSTRACT FROM AUTHOR]

During the previous 2 decades, numerous surgical procedures have become available to treat osteochondral lesions of the talus. The objective of the present study was to use 7 Tesla (7T) magnetic resonance imaging (MRI) to quantify and compare T2 values (a marker of collagen architecture) of native tibiotalar cartilage and cartilage repair tissue in patients treated with a juvenile particulate allograft for osteochondral lesions of the talus. The institutional review board approved the present study, and all subjects provided written informed consent. We scanned the ankles of 7 cartilage repair patients using a 7T MRI scanner with a multi-echo spinecho sequence to measure the cartilage T2 values. We assessed the cartilage T2 values in the talar repair tissue, adjacent native talar cartilage, and overlying tibial cartilage. We compared the differences between groups using the paired t test. The talar cartilage repair tissue demonstrated greater mean T2 relaxation times compared with the native adjacent talar cartilage (64.88 ± 12.23 ms versus 49.56 ± 7.82 ms; p = .043). The tibial cartilage regions overlying these talar cartilage regions demonstrated a trend toward greater T2 relaxation times (77.00 ± 31.29 ms versus 59.52 ± 7.89 ms; p = .067). 7T MRI can detect differences in T2 values in cartilage repair tissue compared with native cartilage and could be useful for monitoring the status of cartilage health after surgical intervention. [ABSTRACT FROM AUTHOR]

Purpose To assess the possible utility of machine learning for classifying subjects with and subjects without osteoarthritis using sodium magnetic resonance imaging data. Theory: support vector machine, k-nearest neighbors, naïve Bayes, discriminant analysis, linear regression, logistic regression, neural networks, decision tree, and tree bagging were tested. Methods Sodium magnetic resonance imaging with and without fluid suppression by inversion recovery was acquired on the knee cartilage of 19 controls and 28 osteoarthritis patients. Sodium concentrations were measured in regions of interests in the knee for both acquisitions. Mean (MEAN) and standard deviation (STD) of these concentrations were measured in each regions of interest, and the minimum, maximum, and mean of these two measurements were calculated over all regions of interests for each subject. The resulting 12 variables per subject were used as predictors for classification. Results Either Min [STD] alone, or in combination with Mean [MEAN] or Min [MEAN], all from fluid suppressed data, were the best predictors with an accuracy >74%, mainly with linear logistic regression and linear support vector machine. Other good classifiers include discriminant analysis, linear regression, and naïve Bayes. Conclusion Machine learning is a promising technique for classifying osteoarthritis patients and controls from sodium magnetic resonance imaging data. Magn Reson Med 74:1435-1448, 2015. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

In vivo MRI has revolutionized the diagnosis and treatment of musculoskeletal disorders over the past 3 decades. Traditionally performed at 1.5 T, MRI at higher field strengths offers several advantages over lower field strengths including increased signal-to-noise ratio, higher spatial resolution, improved spectral resolution for spectroscopy, improved sensitivity for X-nucleus imaging, and decreased image acquisition times. However, the physics of imaging at higher field strengths also presents technical challenges. These include B0 and B1+ field inhomogeneity, design and construction of dedicated radiofrequency (RF) coils for use at high field, increased chemical shift and susceptibility artifacts, increased RF energy deposition (specific absorption rate), increased metal artifacts, and changes in relaxation times compared with the lower field scanners. These challenges were overcome in optimizing high-field (HF) (3 T) MRI over a decade ago. HF MRI systems have since gained universal acceptance for clinical musculoskeletal imaging and have also been widely utilized for the study of musculoskeletal anatomy and physiology. Recently there has been an increasing interest in exploring musculoskeletal applications of ultrahigh field (UHF) (7 T) systems. However, technical challenges similar to those encountered when moving from 1.5 T to 3 T have to be overcome to optimize 7 T musculoskeletal imaging. In this narrative review, we discuss the many potential opportunities and technical challenges presented by the HF and UHF MRI systems. We highlight recent developments in in vivo imaging of musculoskeletal tissues that benefit most from HF imaging including cartilage, skeletal muscle, and bone. [ABSTRACT FROM AUTHOR]

Magnetic resonance imaging (MRI) offers the direct visualization of the human musculoskeletal (MSK) system, especially all diarthrodial tissues including cartilage, bone, menisci, ligaments, tendon, hip, synovium, etc. Conventional MRI techniques based on T1 - and T2 -weighted, proton density (PD) contrast are inconclusive in quantifying early biochemically degenerative changes in MSK system in general and articular cartilage in particular. In recent years, quantitative MR parameter mapping techniques have been used to quantify the biochemical changes in articular cartilage, with a special emphasis on evaluating joint injury, cartilage degeneration, and soft tissue repair. In this article we focus on cartilage biochemical composition, basic principles of T1ρ MRI, implementation of T1ρ pulse sequences, biochemical validation, and summarize the potential applications of the T1ρ MRI technique in MSK diseases including osteoarthritis (OA), anterior cruciate ligament (ACL) injury, and knee joint repair. Finally, we also review the potential advantages, challenges, and future prospects of T1ρ MRI for widespread clinical translation. [ABSTRACT FROM AUTHOR]

Magnetic resonance imaging (MRI) offers the direct visualization of the human musculoskeletal (MSK) system, especially all diarthrodial tissues including cartilage, bone, menisci, ligaments, tendon, hip, synovium, etc. Conventional MRI techniques based on T1- and T2-weighted, proton density (PD) contrast are inconclusive in quantifying early biochemically degenerative changes in MSK system in general and articular cartilage in particular. In recent years, quantitative MR parameter mapping techniques have been used to quantify the biochemical changes in articular cartilage, with a special emphasis on evaluating joint injury, cartilage degeneration, and soft tissue repair. In this article we focus on cartilage biochemical composition, basic principles of T1ρ MRI, implementation of T1ρ pulse sequences, biochemical validation, and summarize the potential applications of the T1ρ MRI technique in MSK diseases including osteoarthritis (OA), anterior cruciate ligament (ACL) injury, and knee joint repair. Finally, we also review the potential advantages, challenges, and future prospects of T1ρ MRI for widespread clinical translation. J. Magn. Reson. Imaging 2015;41:586-600. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Purpose To explore the feasibility of T1rho mapping of menisci at 3T in discriminating between patients with acute anterior cruciate ligament (ACL) injury and healthy controls. Materials and Methods Thirty-three subjects were included in the study and subdivided into two subgroups: 16 healthy controls (4 females, 12 males; mean age = 34.4 ± 10.2 years, age range 24-63 years), 17 patients with ACL injury (3 females, 14 males; mean age = 29.8 ± 10.8 years, age range 18-61 years). T1rho images from all subjects were acquired on a 3T MR scanner using a spin-lock-based 3D GRE sequence and computed for T1rho mapping. Clinical proton density (PD)-weighted fast spin echo (FSE) images in the sagittal (without fat saturation), axial, and coronal (fat-saturated) planes were also acquired for cartilage assessment using Whole-Organ MR Imaging Score (WORMS) grading. Mixed model two-way analysis of variance (ANOVA) was performed to determine whether there were any significant differences among subregional, compartmental, and whole structure T1rho values of meniscus between healthy controls and ACL-injured patients. Results Lateral posterior (29 ± 8 msec) and medial central (25 ± 7 msec) meniscus subregions in healthy controls had significantly lower T1rho values ( P < 0.05) than the corresponding meniscus subregions in ACL-injured patients. Significantly lower meniscus T1rho values ( P < 0.05) were also identified in lateral compartment in healthy controls (26 ± 6 msec) than that of ACL-injured patients (33 ± 4 msec). Subjects' total WORMS between healthy controls and ACL-injured patients had significant differences ( P < 0.05). Conclusions These preliminary results indicate that T1rho mapping is possibly feasible in detecting meniscus degeneration and may be useful in distinguishing ACL-injured patients. J. Magn. Reson. Imaging 2015;41:544-549.© 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Purpose To compare and assess subregional, compartmental, and whole T1rho values of menisci in patients with doubtful-minimal (Kellgren-Lawrence [KL] grade 1-2) as compared to moderate-severe (KL3-4) osteoarthritis (OA) and healthy controls at 3 Tesla (T). Materials and Methods Forty-six subjects were included in the study and subdivided into three subgroups: 16 healthy controls (4 females, 12 males; mean age = 34.4 ± 10.2 years; age range, 24-63 years), 20 patients with doubtful-minimal (KL1-2) OA (9 females, 11 males; mean age = 61.9 ± 10.8 years; age range, 40-80 years), and 10 patients with moderate-severe (KL3-4) OA (4 females, 6 males; mean age = 71.1 ± 9.6 years; age range, 58-89 years). All subjects were evaluated on a 3T MR scanner using a spin-lock-based three-dimensional GRE sequence for T1rho mapping. Clinical proton density (PD)-weighted fast spin echoes (FSE) images in the sagittal (without fat saturation), axial, and coronal (fat-saturated) planes were acquired for cartilage Whole-Organ MR Imaging Score (WORMS) grading. Analysis of covariance was performed to determine whether there were any statistically significant differences between subregional, compartmental, and whole T1rho values of meniscus among healthy controls, OA patients with KL1-2 and with KL3-4. Results Lateral anterior (median ± interquartile range: 26 ± 3 ms) and medial posterior (29 ± 6 ms) meniscus subregions in healthy controls had significantly lower T1rho values ( P < 0.05) than the corresponding meniscus subregions in both KL1-2 (29 ± 7 ms and 35 ± 8 ms, respectively) and KL3-4 (30 ± 12 ms and 40 ± 13 ms, respectively) OA subjects. Significantly lower meniscus T1rho values ( P < 0.05) were also identified in the medial compartment in healthy controls (28 ± 5 ms) relative to both KL1-2 OA subjects and KL3-4 OA subjects (32 ± 7 ms and 37 ± 7 ms, respectively). The entire meniscus T1rho values in healthy controls (28 ± 4 ms) were significantly lower than those of both KL1-2 and KL3-4 OA subjects (33 ± 6 ms and 34 ± 6 ms, respectively). Conclusion Significant elevations of T1rho values in specific regions of menisci in both KL1-2 and KL3-4 OA patients indicate that T1rho mapping may be sensitive to meniscus degeneration. The preliminary results suggest that damage in the medial posterior subregion and medial compartment of menisci may possibly be associated with osteoarthritis. J. Magn. Reson. Imaging 2014;40:588-595. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Purpose To demonstrate the feasibility of performing bone microarchitecture, high-resolution cartilage, and clinical imaging of the hip at 7T. Materials and Methods This study had Institutional Review Board approval. Using an 8-channel coil constructed in-house, we imaged the hips of 15 subjects on a 7T magnetic resonance imaging (MRI) scanner. We applied: 1) a T1-weighted 3D fast low angle shot (3D FLASH) sequence (0.23 × 0.23 × 1-1.5 mm3) for bone microarchitecture imaging; 2) T1-weighted 3D FLASH (water excitation) and volumetric interpolated breath-hold examination (VIBE) sequences (0.23 × 0.23 × 1.5 mm3) with saturation or inversion recovery-based fat suppression for cartilage imaging; 3) 2D intermediate-weighted fast spin-echo (FSE) sequences without and with fat saturation (0.27 × 0.27 × 2 mm) for clinical imaging. Results Bone microarchitecture images allowed visualization of individual trabeculae within the proximal femur. Cartilage was well visualized and fat was well suppressed on FLASH and VIBE sequences. FSE sequences allowed visualization of cartilage, the labrum (including cartilage and labral pathology), joint capsule, and tendons. Conclusion This is the first study to demonstrate the feasibility of performing a clinically comprehensive hip MRI protocol at 7T, including high-resolution imaging of bone microarchitecture and cartilage, as well as clinical imaging. J. Magn. Reson. Imaging 2014;39:1384-1393. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Object: Our objective was to use 7 T MRI to compare cartilage morphology (thickness) and collagen composition (T2 values) in cartilage repair patients and healthy controls. Materials and methods: We scanned the knees of 11 cartilage repair patients and 11 controls on a 7 T MRI scanner using a high-resolution, gradient-echo sequence to measure cartilage thickness and a multi-echo spin-echo sequence to measure cartilage T2 values. We used two-tailed t tests to compare cartilage thickness and T2 values in: repair tissue (RT) versus adjacent cartilage (AC); RT versus healthy control cartilage (HC); AC versus HC. Results: Mean thickness in RT, AC, HC were: 2.2 ± 1.4, 3.6 ± 1.1, 3.3 ± 0.7 mm. Differences in thickness between RT–AC ( p = 0.01) and RT–HC ( p = 0.02) were significant, but not AC–HC ( p = 0.45). Mean T2 values in RT, AC, HC were: 51.6 ± 7.6, 40.0 ± 4.7, 45.9 ± 3.7 ms. Differences in T2 values between RT–AC ( p = 0.0005), RT-HC ( p = 0.04), and AC–HC ( p = 0.004) were significant. Conclusion: 7 T MRI allows detection of differences in morphology and collagen architecture in: (1) cartilage repair tissue compared to adjacent cartilage and (2) cartilage repair tissue compared to cartilage from healthy controls. Although cartilage adjacent to repair tissue may be normal in thickness, it can demonstrate altered collagen composition. [ABSTRACT FROM AUTHOR]

The critical design aim for a sodium/proton coil is to maximize sodium sensitivity and transmit field homogeneity while simultaneously providing adequate proton sensitivity and homogeneity. While most dual-frequency coils use lossy high-impedance trap circuits or PIN diodes to allow dual-resonance, we explored a nested-coil design for sodium/proton knee imaging at 7 T. A stand-alone eight-channel sodium receive array was implemented without standard dual-resonance circuitry to provide improved sodium signal-to-noise ratio. A detunable sodium birdcage was added for homogeneous sodium excitation and a four-channel proton transmit-receive array was added to provide anatomical reference imaging and B0 shimming capabilities. Both additional modules were implemented with minimal disturbance to the eight-channel sodium array by managing their respective resonances and geometrical arrangement. In vivo sodium signal-to-noise ratio was 1.2-1.7 times greater in the developed eight-channel array than in a mononuclear sodium birdcage coil, whereas the developed four-channel proton array provided signal-to-noise ratio similar to that of a commercial mononuclear proton birdcage coil. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Osteoarthritis (OA) is the most common musculoskeletal degenerative disease, affecting millions of people. Although OA has been considered primarily a cartilage disorder associated with focal cartilage degeneration, it is accompanied by well-known changes in subchondral and trabecular bone, including sclerosis and osteophyte formation. The exact cause of OA initiation and progression remains under debate, but OA typically first affects weightbearing joints such as the knee. Magnetic resonance imaging (MRI) has been recognized as a potential tool for quantitative assessment of cartilage abnormalities due to its excellent soft tissue contrast. Over the last two decades, several new MR biochemical imaging methods have been developed to characterize the disease process and possibly predict the progression of knee OA. These new MR biochemical methods play an important role not only for diagnosis of disease at an early stage, but also for their potential use in monitoring outcome of various drug therapies (success or failure). Recent advances in multicoil radiofrequency technology and high field systems (3 T and above) significantly improve the sensitivity and specificity of imaging studies for the diagnosis of musculoskeletal disorders. The current state-of-the-art MR imaging methods are briefly reviewed for the quantitative biochemical and functional imaging assessment of musculoskeletal systems. [ABSTRACT FROM AUTHOR]

Glycosaminogycans (GAGs) are involved in numerous vital functions in the human body. Mapping the GAG concentration in vivo is desirable for the diagnosis and monitoring of a number of diseases such as osteoarthritis. which affects millions of individuals. GAG loss in cartilage is typically an initiating event in osteoarthritis. Another widespread pathology related to GAG is inter-vertebral disk degeneration. Currently existing techniques for GAG monitoring, such as delayed gadolinium-enhanced MRI contrast (dGEMRIC), T1p, and 23Na MRI. have some practical limitations. We show that by exploiting the exchangeable protons of GAG one may directly measure the localized GAG concentration in vivo with high sensitivity and therefore obtain a powerful diagnostic MRI method. [ABSTRACT FROM AUTHOR]

: Rationale and ObjectivesThe purpose of this study was (a) to demonstrate the feasibility of computing T1ρ maps of, and T1ρ dispersion in, human wrist cartilage at MR imaging in vivo and (b) to compare T1ρ and T2 weighting in terms of magnitude of relaxation times and signal intensity contrast.: Materials and MethodsT2 and T1ρ magnetic resonance images of wrist joints in healthy volunteers (n = 5) were obtained with a spin-echo sequence and a fast spin-echo sequence pre-encoded with a spin-lock pulse cluster. A 1.5-T clinical imager was used (Signa; GE Medical Systems, Milwaukee, Wis) with a 9.5-cm-diameter transmit-receive quadrature birdcage coil tuned to 63.75 MHz.: ResultsT1ρ relaxation times at a spin-lock frequency of 500 Hz vary from 40.5 msec ± 0.85 to 56.6 msec ± 4.83, and T2 relaxation times vary from 28.1 msec ± 1.88 to 34.5 msec ± 2.63 (mean ± standard error of the mean, n = 5, P < .016) in various regions of the wrist. T1ρ dispersion was observed in the range of spin-lock frequencies studied. T1ρ-weighted images not only have higher signal-to-noise ratios but also show better fluid and fat signal suppression than T2-weighted images.: ConclusionIt was possible to perform T2- and T1ρ-weighted MR imaging of human wrist cartilage in vivo with standard clinical imagers. The higher signal-to-noise ratio and improved contrast between cartilage and surrounding fat achieved with T1ρ imaging may provide better definition of lesions and accurate quantitation of small changes in cartilage degeneration. [Copyright &y& Elsevier]

In this study we use undersampled MRI acquisition methods to obtain accelerated 3D mono and biexponential spin–lattice relaxation time in the rotating frame (T1ρ) mapping of knee cartilage, reducing the usual long scan time. We compare the accelerated T1ρ maps obtained by deep learning-based variational network (VN) and compressed sensing (CS). Both methods were compared with spatial (S) and spatio-temporal (ST) filters. Complex-valued fitting was used for T1ρ parameters estimation. We tested with seven in vivo and six synthetic datasets, with acceleration factors (AF) from 2 to 10. Median normalized absolute deviation (MNAD), analysis of variance (ANOVA), and coefficient of variation (CV) were used for analysis. The methods CS-ST, VN-S, and VN-ST performed well for accelerating monoexponential T1ρ mapping, with MNAD around 5% for AF = 2, which increases almost linearly with the AF to an MNAD of 13% for AF = 8, with all methods. For biexponential mapping, the VN-ST was the best method starting with MNAD of 7.4% for AF = 2 and reaching MNAD of 13.1% for AF = 8. The VN was able to produce 3D-T1ρ mapping of knee cartilage with lower error than CS. The best results were obtained by VN-ST, improving CS-ST method by nearly 7.5%. [ABSTRACT FROM AUTHOR]

In the field of sodium magnetic resonance imaging (MRI), inversion recovery (IR) is a convenient and popular method to select sodium in different environments. For the knee joint, IR has been used to suppress the signal from synovial fluids, which improves the correlation between the sodium signal and the concentration of glycosaminoglycans (GAGs) in cartilage tissues. For the better inversion of the magnetization vector under the spatial variations of the B 0 and B 1 fields, the IR sequence usually employ adiabatic pulses as the inversion pulse. On the other hand, it has been shown that RF shapes robust against the variations of the B 0 and B 1 fields can be generated by numerical optimization based on optimal control theory. In this work, we compare the performance of fluid-suppressed sodium MRI on the knee joint in vivo , between one implemented with an adiabatic pulse in the IR sequence and the other with the adiabatic pulse replaced by an optimal-control shaped pulse. While the optimal-control pulse reduces the RF power deposited to the body by 58%, the quality of fluid suppression and the signal level of sodium within cartilage are similar between two implementations. [ABSTRACT FROM AUTHOR]

Abstract: Objective: To assess and compare subregional and whole T1rho values (median±interquartile range) of femorotibial cartilage and menisci in patients with doubtful (Kellgren–Lawrence (KL) grade 1) to severe (KL4) osteoarthritis (OA) at 3T. Materials and methods: 30 subjects with varying degrees of OA (KL1–4, 13 females, 17 males, mean age±SD=63.9±13.1 years) were evaluated on a 3T MR scanner using a spin-lock-based 3D GRE sequence for T1rho mapping. Clinical proton density (PD)-weighted fast spin echo (FSE) images in sagittal (without fat saturation), axial, and coronal (fat-saturated) planes were acquired for cartilage and meniscus Whole-organ MR imaging score (WORMS) grading. Wilcoxon rank sum test was performed to determine whether there were any statistically significant differences between subregional and whole T1rho values of femorotibial cartilage and menisci in subjects with doubtful to severe OA. Results: Lateral (72±10ms, median±interquartile range) and medial (65±10ms) femoral anterior cartilage subregions in moderate–severe OA subjects had significantly higher T1rho values (P <0.05) than cartilage subregions and whole femorotibial cartilage in doubtful–minimal OA subjects. There were statistically significant differences in meniscus T1rho values of the medial posterior subregion of subjects with moderate–severe OA and T1rho values of all subregions and the whole meniscus in subjects with doubtful–minimal OA. When evaluated based on WORMS, statistically significant differences were identified in T1rho values between the lateral femoral anterior cartilage subregion in patients with WORMS5–6 (advanced degeneration) and whole femorotibial cartilage and all cartilage subregions in patients with WORMS0–1 (normal). Conclusion: T1rho values are higher in specific meniscus and femorotibial cartilage subregions. These findings suggest that regional damage of both femorotibial hyaline cartilage and menisci may be associated with osteoarthritis. [Copyright &y& Elsevier]

Abstract: Sodium MRI has been shown to be highly specific for glycosaminoglycan (GAG) content in articular cartilage, the loss of which is an early sign of osteoarthritis (OA). Quantitative sodium MRI techniques are therefore under development in order to detect and assess early biochemical degradation of cartilage, but due to low sodium NMR sensitivity and its low concentration, sodium images need long acquisition times (15–25min) even at high magnetic fields and are typically of low resolution. In this preliminary study, we show that compressed sensing can be applied to reduce the acquisition time by a factor of 2 at 7T without losing sodium quantification accuracy. Alternatively, the nonlinear reconstruction technique can be used to denoise fully-sampled images. We expect to even further reduce this acquisition time by using parallel imaging techniques combined with SNR-improved 3D sequences at 3T and 7T. [Copyright &y& Elsevier]

Abstract: The loss of proteoglycans (PG) in the articular cartilage is an early signature of osteoarthritis (OA). The ensuing changes in the fixed charge density in the cartilage can be directly linked to sodium concentration via charge balance. Sodium ions in the knee joint appear in two pools: in the synovial fluids or joint effusion where the ions are in free motion and bound within the cartilage tissue where the Na+ ions have a restricted motion. The ions in these two compartments have therefore different T 1 and T 2 relaxation times. The purpose of this study is to demonstrate the feasibility of a fluid-suppressed 3D ultrashort TE radial sodium sequence by implementing an inversion recovery (IR) preparation of the magnetization at 7T. This method could allow a more accurate and more sensitive quantification of loss of PG in patients with OA. It is shown that adiabatic pulses offer significantly improved performance in terms of robustness to B 1 and B 0 inhomogeneities when compared to the hard pulse sequence. Power deposition considerations further pose a limit to the RF inversion power, and we demonstrate in simulations and experiments how a practical compromise can be struck between clean suppression of fluid signals and power deposition levels. Two IR sequences with different types of inversion pulses (a rectangular pulse and an adiabatic pulse) were tested on a liquid phantom, ex vivo on a human knee cadaver and then in vivo on five healthy volunteers, with a (Nyquist) resolution of ∼3.6mm and a signal-to-noise ratio of ∼30 in cartilage without IR and ∼20 with IR. Due to specific absorption rate limitations, the total acquisition time was ∼17min for the 3D radial sequence without inversion or with the rectangular IR, and 24:30min for the adiabatic IR sequence. It is shown that the adiabatic IR sequence generates a more uniform fluid suppression over the whole sample than the rectangular IR sequence. [Copyright &y& Elsevier]