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Background: Three-dimensional MR fingerprinting (3D-MRF) has been increasingly used to assess cartilage degeneration, particularly in the knee joint, by looking into multiple relaxation parameters. A comparable 3D-MRF approach can be adapted to assess cartilage degeneration for the hip joint, with changes to accommodate specific challenges of hip joint imaging., Purpose: To demonstrate the feasibility and repeatability of 3D-MRF in the bilateral hip jointly we map proton density (PD), T 1 , T 2 , T 1ρ , and ∆B 1+ in clinically feasible scan times., Study Type: Prospective., Subjects: Eight healthy subjects, three patients with mild osteoarthritis (OA), and one of the OA patients had femoral acetabular impingement (FAI). A National Institute of Standards and Technology/International Society for Magnetic Resonance in Medicine (NIST/ISMRM) system phantom was also used., Field Strength/sequence: 3 T, 3D-MRF sequence for bilateral hip joint mapping. Reference sequences include Volume Interpolated Breath-hold Examination (VIBE) for T 1 mapping, and magnetization-prepared fast low-angle shot (TFL) for T 2 and T 1ρ mapping., Assessment: The signal-to-noise ratio (SNR), repeatability, scan time, and accuracy of T 1 , T 2 , and T 1ρ maps of 3D-MRF sequence were evaluated on a NIST/ISMRM phantom and human subjects. Differences in the parametric maps between OA and healthy subjects were assessed., Statistical Tests: Regression, Bland-Altman, Kruskal-Wallis, and Wilcoxon tests were used to assess for accuracy, repeatability, and subregional variation. The P-value <0.05 indicated statistically significant., Results: A 3D-MRF sequence sensitive to PD, T 1 , T 2 , T 1ρ , and ∆B 1+ within 15 minutes, achieving high SNR and low test-retest coefficient of variance (T 1 : 3.36%, T 2 : 3.99%, T 1ρ : 5.93%). Mild hip OA patients, including one with mild OA and FAI, showed elevation of 29.4 ± 9% (T 2 ) and 32.4 ± 4.4% (T 1ρ ) in femoral lateral compartment of the hip joint compared to healthy controls., Data Conclusion: 3D-MRF may be a feasible approach for simultaneous, quantitative mapping of bilateral hip joint cartilage in healthy and mild OA patients., Evidence Level: 1 TECHNICAL EFFICACY: Stage 1., (© 2024 International Society for Magnetic Resonance in Medicine.)

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 T 1 , T 2 , and T 1ρ 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, T 1 , T 2 , and T 1ρ maps., Assessment: The acquisition of 3D-MRF cartilage (simultaneous acquisition of T 1 , T 2 , and T 1ρ maps) were acquired using a dictionary pattern-matching approach. Conventional cartilage T 1 , T 2 , and T 1ρ 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 T 1 , T 2 , and T 1ρ 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 T 1 , T 2 , and T 1ρ , respectively. The MRF results had a good agreement with the conventional methods with a linear regression slope >0.61 and R 2  > 0.59., Conclusion: The 3D-MRF sequence had high intra-subject and inter-subject repeatabilities for simultaneously measuring knee cartilage T 1 , T 2 , and T 1ρ with good agreement with conventional sequences., Evidence Level: 1 TECHNICAL EFFICACY: Stage 1., (© 2023 International Society for Magnetic Resonance in Medicine.)

Background: Multiparameter characterization using MR fingerprinting (MRF) can quantify multiple relaxation parameters of intervertebral disc (IVD) simultaneously. These parameters may vary by age and sex., Purpose: To investigate age- and sex-related differences in the relaxation parameters of the IVD of the lumbar spine using a multiparameter MRF technique., Study Type: Prospective., Subjects: 17 healthy subjects (8 male; mean age = 34 ± 10 years, range 20-60 years)., Field Strength/sequence: 3D-MRF sequence for simultaneous acquisition of proton density, T 1 , T 2 , and T 1ρ maps at 3.0T., Assessment: Global mean T 1 , T 2 , and T 1ρ of all lumbar IVDs and mean T 1 , T 2 , and T 1ρ of each individual IVD (L1-L5) were measured. Gray level co-occurrence matrix was used to quantify textural features (median, contrast, correlation, energy, and homogeneity) from T 1 , T 2 , and T 1ρ maps., Statistical Tests: Spearman rank correlations (R) evaluated the association between age and T 1 , T 2 , and T 1ρ of IVD. Mann-Whitney U-tests evaluated differences between males and females in T 1 , T 2 , and T 1ρ of IVD. Statistical significance was defined as P-value <0.05., Results: There was a significant negative correlation between age and global mean values of all IVDs for T 1 (R = -0.637), T 2 (R = -0.509), and T 1ρ (R = -0.726). For individual IVDs, there was a significant negative correlation between age and mean T 1 at all IVD segments (R range = -0.530 to -0.708), between age and mean T 2 at L2-L3, L3-L4, and L4-L5 (R range = -0.493 to 0.640), and between age and mean T 1ρ at all segments except L1-L2 (R range = -0.632 to -0.763). There were no significant differences between sexes in global mean T 1 , T 2, and T 1ρ (P-value = 0.23-0.76) The texture features with the highest significant correlations with age for all IVDs were global T 1ρ mean (R = -0.726), T 1 energy (R = -0.681), and T 1 contrast (R = 0.709)., Conclusion: This study showed that the 3D-MRF technique has potential to characterize age-related differences in T 1 , T 2, or T 1ρ of IVD in healthy subjects., Level of Evidence: 2 TECHNICAL EFFICACY: Stage 1., (© 2023 International Society for Magnetic Resonance in Medicine.)

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., (© 2023 International Society for Magnetic Resonance in Medicine.)

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.)

Background: Noninvasive measurement of internal dynamic strain can be potentially useful to characterize spine intervertebral disc (IVD) in the setting of injury or degenerative disease., Purpose: To develop and demonstrate a noninvasive technique to quantify three-dimensional (3D) internal dynamic strains in the IVD using a combination of static mechanical loading of the IVD using a magnetic resonance imaging (MRI)-compatible ergometer., Study Type: Prospective., Subjects: Silicone gel phantom studies were conducted to assess strain variation with load and repeatability. Mechanical testing was done on the phantoms to confirm MR results. Eight healthy human volunteers (four men and four woman, age = 29 ± 5 years) underwent MRI using a rest, static loading, and recovery paradigm. Repeatability tests were conducted in three subjects., Field Strength/sequence: MRI (3 T) with 3D continuous golden-angle radial sparse parallel (GRASP) and compressed sensing (CS) reconstruction., Assessment: CS reconstruction of the images, motion deformation, and Lagrangian strain maps were calculated for five IVD segments from L1/L2 to L5/S1., Statistical Tests: Ranges of displacement and strain in each subject and the resulting mean and standard deviation were calculated. Student t-tests were used to calculate changes in strain from loading to recovery. The correlation coefficient (CC) in the repeatability study was calculated., Results: The most compressive strain experienced by the IVD segments under loaded conditions was in the L4/L5 segment (-7.5 ± 2.9%). The change in minimum strain from load to recovery was the most for the L4/L5 segment (-7.5% to -5.0%, P = 0.026) and the least for the L1/L2 segment (-4.4% to -3.9%, P = 0.51). In vivo repeatability in three subjects shows strong correlation between scans in subjects done 6 months apart, with CCs equal to 0.86, 0.94, and 0.94 along principal directions., Data Conclusion: This study shows the feasibility of using static mechanical loading with continuous GRASP-MRI acquisition with CS reconstruction to measure 3D internal dynamic strains in the spine IVD., Level of Evidence: 2 TECHNICAL EFFICACY STAGE: 1., (© 2021 International Society for Magnetic Resonance in Medicine.)

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., (© 2019 International Society for Magnetic Resonance in Medicine.)

Background: In addition to the articular cartilage, osteoarthritis (OA) affects several other tissues such as tendons, ligaments, and subchondral bone. T1 ρ relaxation study of these short T 2 tissues may provide a more comprehensive evaluation of OA., Purpose: To develop a 3D spin-lattice relaxation in the rotating frame (T 1ρ ) prepared zero echo time (ZTE)-based pointwise encoding time reduction with radial acquisition (3D-T 1ρ -PETRA) sequence for relaxation mapping of semisolid short-T 2 tissues on a clinical 3 T scanner., Study Type: Prospective., Population: Phantom, two bovine whole knee joint and Achilles tendon specimens, 10 healthy volunteers with no known inflammation, trauma or pain in the knee or ankle., Field Strength/sequence: A customized PETRA sequence to acquire fat-suppressed 3D T 1ρ -weighted images tissues with semisolid short T 2 / T 2 * relaxation times in the knee and ankle joints at 3 T., Assessment: Mono- and biexponential T 1ρ relaxation components were assessed in the patellar tendon (PT), anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), and Achilles tendon (AT)., Statistical Tests: Kruskal-Wallis with post-hoc Dunn's test for multiple pairwise comparisons., Results: Phantom and ex vivo studies showed the feasibility of T 1ρ relaxation mapping using the proposed 3D-T 1ρ -PETRA sequence. The in vivo study demonstrated an averaged mono-T 1ρ relaxation of (median [IQR]) 15.9 [14.5] msec, 23.6 [9.4] msec, 17.4 [7.4] msec, and 5.8 [10.2] msec in the PT, ACL, PCL, and AT, respectively. The bicomponent analysis showed the short and long components (with their relative fractions) of 0.65 [1.0] msec (46.9 [15.3]%) and 37.3 [18.4] msec (53.1 [15.3]%) for PT, 1.7 [2.1] msec (42.5 [12.5]%) and 43.7 [17.8] msec (57.5 [12.5]%) for ACL, and 1.2 [1.9] msec (42.6 [14.0]%) and 27.7 [14.7] msec (57.3 [14.0]%) for PCL and 0.4 [0.02] msec (58.8 [13.3]%/) and 31.3 [10.8] msec (41.2 [13.3]%) for AT. Statistically significant (P ≤ 0.05) differences were observed in the mono- and biexponential relaxation between several regions., Data Conclusion: The 3D-T 1ρ -PETRA sequence allows volumetric, isotropic (0.78 × 0.78 × 0.78 mm), biexponential T 1ρ assessment with corresponding fractions of the tissues with semisolid short T 2 / T 2 * ., Level of Evidence: 2 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2019;50:1207-1218., (© 2019 International Society for Magnetic Resonance in Medicine.)

Background: Measuring T 1ρ in the knee menisci can potentially be used as noninvasive biomarkers in detecting early-stage osteoarthritis (OA)., Purpose: To demonstrate the feasibility of biexponential T 1ρ relaxation mapping of human knee menisci., Study Type: Prospective., Population: Eight healthy volunteers with no known inflammation, trauma, or pain in the knee and three symptomatic subjects with early knee OA., Field Strength/sequence: Customized Turbo-FLASH sequence to acquire 3D-T 1ρ -weighted images on a 3 T MRI scanner., Assessment: T 1ρ relaxation values were assessed in 11 meniscal regions of interest (ROIs) using monoexponential and biexponential models., Statistical Tests: Nonparametric rank-sum tests, Kruskal-Wallis test, and coefficient of variation., Results: The mean monoexponential T 1ρ relaxation in the lateral menisci were 28.05 ± 4.2 msec and 37.06 ± 10.64 msec for healthy subjects and early knee OA patients, respectively, while the short and long components were 8.07 ± 0.5 msec and 72.35 ± 3.2 msec for healthy subjects and 2.63 ± 2.99 msec and 55.27 ± 24.76 msec for early knee OA patients, respectively. The mean monoexponential T 1ρ relaxation in the medial menisci were 34.30 ± 3.8 msec and 37.26 ± 11.38 msec for healthy and OA patients, respectively, while the short and long components were 7.76 ± 0.7 msec and 72.19 ± 4.2 msec for healthy subjects and 3.06 ± 3.24 msec and 55.27 ± 24.59 msec for OA patients, respectively. Statistically significant (P ≤ 0.05) differences were observed in the monoexponential relaxation between some of the ROIs. The T 1ρ,short was significantly lower (P = 0.02) in the patients than controls. The rmsCV% ranges were 1.51-16.6%, 3.59-14.3%, and 4.91-15.6% for T 1ρ -mono, T 1ρ -short, and T 1ρ -long, respectively., Data Conclusion: Our results showed that in all ROIs, T 1ρ relaxation times of outer zones (red zones) were less than inner zones (white zones). Monoexponential T 1ρ was increased in medial, lateral, and body menisci of early OA while the biexponential numbers were decreased in early OA patients., Level of Evidence: 2 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2019. J. Magn. Reson. Imaging 2019;50:824-835., (© 2019 International Society for Magnetic Resonance in Medicine.)

Background: Osteoporosis (OP) results in weak bone and can ultimately lead to fracture. Drugs such as glucocorticoids can also induce OP (glucocorticoid-induced osteoporosis [GIO]). Bone marrow adipose tissue composition and quantity may play a role in OP pathophysiology, but has not been thoroughly studied in GIO compared to primary OP., Purpose/hypothesis: Chemical shift-encoded (CSE) MRI allows detection of subregional differences in bone marrow adipose tissue composition and quantity in the proximal femur of GIO compared to OP subjects and has high agreement with the reference standard of magnetic resonance spectroscopy (MRS)., Study Type: Prospective., Subjects: In all, 18 OP and 13 GIO subjects., Fields Strength: 3T., Sequence: Multiple gradient-echo, stimulated echo acquisition mode (STEAM)., Assessment: Subjects underwent CSE-MRI in the proximal femurs, and for each parametric map regions of interest (ROIs) were assessed in the femoral head (fHEAD), femoral neck (fNECK), Ward's triangle (fTRIANGLE), and the greater trochanter (GTROCH). In addition, we compared CSE-MRI against the reference standard of MRS performed in the femoral neck and Ward's triangle., Statistical Tests: Differences between OP/GIO were investigated using the Mann-Whitney nonparametric test. Bland-Altman methodology was used to assess measurement agreement between CSE-MRI and MRS., Results: GIO compared with OP subjects demonstrated: decreased monounsaturated fat fraction (MUFA) (-2.1%, P < 0.05) in fHEAD; decreased MUFA (-3.8%, P < 0.05), increased saturated fat fraction (SFA) (5.5%, P < 0.05), and decreased T 2 * (-3.8 msec, P < 0.05) in fNECK; decreased proton density fat fraction (PDFF) (-15.1%, P < 0.05), MUFA (-9.8%, P < 0.05), polyunsaturated fat fraction (PUFA) (-1.8%, P < 0.01), increased SFA (11.6%, P < 0.05), and decreased T 2 * (-5.4 msec, P < 0.05) in fTRIANGLE; and decreased T 2 * (-1.5 msec, P < 0.05) in GTROCH. There was high measurement agreement between MRI and MRS using the Bland-Altman test., Data Conclusion: 3T CSE-MRI may allow reliable assessment of subregional bone marrow adipose tissue (bMAT) quantity and composition in the proximal femur in a clinically reasonable scan time. Glucocorticoids may alter the lipid profile of bMAT and potentially result in reduced bone quality., Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:490-496., (© 2018 International Society for Magnetic Resonance in Medicine.)

Synovitis and joint effusion are common manifestations of rheumatic disease and play an important role in the disease pathophysiology. Earlier detection and accurate assessment of synovial pathology, therefore, can facilitate appropriate clinical management and hence improve prognosis. Magnetic resonance imaging (MRI) allows unparalleled assessment of all joint structures and associated pathology. It has emerged as a powerful tool, which enables not only detection of synovitis and effusion, but also allows quantification, detailed characterization, and noninvasive monitoring of synovial processes. The purpose of this article is to summarize the pathophysiology of synovitis and to review the role of qualitative, semiquantitative, and quantitative MRI in the assessment of synovitis and joint fluid. We also discuss the utility of MRI as an outcome measure to assess treatment response, particularly with respect to osteoarthritis and rheumatoid arthritis. Emerging applications such as hybrid positron emission tomography / MRI and molecular imaging are also briefly discussed. Level of Evidence: 5 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2019., (© 2019 International Society for Magnetic Resonance in Medicine.)

Background: The progressive loss of hyaline articular cartilage due to osteoarthritis (OA) changes the functional and biochemical properties of cartilage. Measuring the T 1 ρ along with the morphological assessment can potentially be used as noninvasive biomarkers in detecting early-stage OA. To correlate the biochemical and morphological data, submillimeter isotropic resolution for both studies is required., Purpose: To implement a high spatial resolution 3D-isotropic-MRI sequence for simultaneous assessment of morphological and biexponential T 1 ρ relaxometry of human knee cartilage in vivo., Study Type: Prospective., Population: Ten healthy volunteers with no known inflammation, trauma, or pain in the knee., Field Strength/sequence: Standard FLASH sequence and customized Turbo-FLASH sequence to acquire 3D-isotropic-T 1 ρ-weighted images on a 3T MRI scanner., Assessment: The mean volume and thickness along with mono- and biexponential T 1 ρ relaxations were assessed in the articular cartilage of 10 healthy volunteers., Statistical Tests: Nonparametric rank-sum tests. Bland-Altman analysis and coefficient of variation., Results: The mean monoexponential T 1 ρ relaxation was 40.7 ± 4.8 msec, while the long and short components were 58.2 ± 3.9 msec and 6.5 ± 0.6 msec, respectively. The mean fractions of long and short T 1 ρ relaxation components were 63.7 ± 5.9% and 36.3 ± 5.9%, respectively. Statistically significant (P ≤ 0.03) differences were observed in the monoexponential and long components between some of the regions of interest (ROIs). No gender differences between biexponential components were observed (P > 0.05). Mean cartilage volume and thickness were 25.9 ± 6.4 cm 3 and 2.2 ± 0.7 mm, respectively. Cartilage volume (P = 0.01) and thickness (P = 0.03) were significantly higher in male than female participants across all ROIs. Bland-Altman analysis showed agreement between two morphological methods with limits of agreement between -1000 mm 3 and +1100 mm 3 for volume, and -0.78 mm and +0.46 mm for thickness, respectively., Data Conclusion: Simultaneous assessment of morphological and multicomponent T 1 ρ relaxation of knee joint with 0.7 × 0.7 × 0.7 mm isotropic spatial resolution is demonstrated in vivo. Comparison with a standard method showed that the proposed technique is suitable for assessing the volume and thickness of articular cartilage., Level of Evidence: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;48:1707-1716., (© 2018 International Society for Magnetic Resonance in Medicine.)

More than a decade after the introduction of compressed sensing (CS) in MRI, researchers are still working on ways to translate it into different research and clinical applications. The greatest advantage of CS in MRI is the reduced amount of k-space data needed to reconstruct images, which can be exploited to reduce scan time or to improve spatial resolution and volumetric coverage. Efficient data acquisition using CS is extremely important for compositional mapping of the musculoskeletal system in general and knee cartilage mapping techniques in particular. High-resolution quantitative information about tissue biochemical composition could be obtained in just a few minutes using CS MRI. However, in order to make this goal a reality, some issues still need to be addressed. In this article we review the current state of the art of CS methods for rapid compositional mapping of knee cartilage. Specifically, data acquisition strategies, image reconstruction algorithms, and data fitting models are discussed. Different CS studies for T 2 and T 1ρ mapping of knee cartilage are reviewed, with illustrative results. Future directions, opportunities, and challenges of rapid compositional mapping techniques are also discussed. Level of Evidence: 4 Technical Efficacy: Stage 6 J. Magn. Reson. Imaging 2018;47:1185-1198., (© 2018 International Society for Magnetic Resonance in Medicine.)

Purpose: To evaluate biexponential T 2 relaxation mapping of human knee cartilage in vivo in clinically feasible scan times., Materials and Methods: T 2 -weighted magnetic resonance (MR) images were acquired from eight healthy volunteers using a standard 3T clinical scanner. A 3D Turbo-Flash sequence was modified to enable T 2 -weighted imaging with different echo times. Series of T 2 -weighted images were fitted using mono- and biexponential models with two- and four-parametric nonlinear approaches, respectively., Results: Biexponential relaxation of T 2 was detected in the knee cartilage in five regions of interest in all eight healthy volunteers. Short/long relaxation components of T 2 were estimated to be 8.27 ± 0.68 / 45.35 ± 3.79 msec with corresponding fractions of 41.3 ± 1.1% / 58.6 ± 4.6%, respectively. The monoexponential relaxation of T 2 was measured to be 26.9 ± 2.27 msec. The experiments showed good repeatability with coefficient of variation root mean square (CV rms ) < 18% in all regions. The only difference in gender was observed in medial tibial cartilage, where the biexponential T 2 in female volunteers was significantly higher compared to male volunteers (P = 0.014). Significant differences were observed in T 2 relaxation between different regions on interest., Conclusion: Biexponential relaxation of T 2 was observed in the human knee cartilage in vivo. The short and long components are thought to be related to the tightly bound and loosely bound macromolecular water compartments. These preliminary results of biexponential T 2 analysis could potentially be used to increase the specificity for detection of early osteoarthritis by measuring different water compartments and their fractions., Level of Evidence: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:809-819., (© 2017 International Society for Magnetic Resonance in Medicine.)

Osteoporosis is a disease of weak bone and increased fracture risk caused by low bone mass and microarchitectural deterioration of bone tissue. The standard-of-care test used to diagnose osteoporosis, dual-energy x-ray absorptiometry (DXA) estimation of areal bone mineral density (BMD), has limitations as a tool to identify patients at risk for fracture and as a tool to monitor therapy response. Magnetic resonance imaging (MRI) assessment of bone structure and microarchitecture has been proposed as another method to assess bone quality and fracture risk in vivo. MRI is advantageous because it is noninvasive, does not require ionizing radiation, and can evaluate both cortical and trabecular bone. In this review article, we summarize and discuss research progress on MRI of bone structure and microarchitecture over the last decade, focusing on in vivo translational studies. Single-center, in vivo studies have provided some evidence for the added value of MRI as a biomarker of fracture risk or treatment response. Larger, prospective, multicenter studies are needed in the future to validate the results of these initial translational studies., Level of Evidence: 5 Technical Efficacy: Stage 5 J. MAGN. RESON. IMAGING 2017;46:323-337., (© 2017 International Society for Magnetic Resonance in Medicine.)

Background: Glucocorticoid-induced osteoporosis (GIO) is the most common secondary form of osteoporosis, and glucocorticoid users are at increased risk for fracture compared with nonusers. There is no established relationship between bone mineral density (BMD) and fracture risk in GIO. We used 3 Tesla (T) MRI to investigate how proximal femur microarchitecture is altered in subjects with GIO., Methods: This study had institutional review board approval. We recruited 6 subjects with long-term (> 1 year) glucocorticoid use (median age = 52.5 (39.2-58.7) years) and 6 controls (median age = 65.5 [62-75.5] years). For the nondominant hip, all subjects underwent dual-energy x-ray absorptiometry (DXA) to assess BMD and 3T magnetic resonance imaging (MRI, 3D FLASH) to assess metrics of bone microarchitecture and strength., Results: Compared with controls, glucocorticoid users demonstrated lower femoral neck trabecular number (-50.3%, 1.12 [0.84-1.54] mm(-1) versus 2.27 [1.88-2.73] mm(-1) , P = 0.02), plate-to-rod ratio (-20.1%, 1.48 [1.39-1.71] versus 1.86 [1.76-2.20], P = 0.03), and elastic modulus (-64.8% to -74.8%, 1.54 [1.22-3.19] GPa to 2.31 [1.87-4.44] GPa versus 6.15 [5.00-7.09] GPa to 6.59 [5.58-7.31] GPa, P < 0.05), and higher femoral neck trabecular separation (+192%, 0.705 [0.462-1.00] mm versus 0.241 [0.194-0.327] mm, P = 0.02). There were no differences in femoral neck trabecular thickness (-2.7%, 0.193 [0.184-0.217] mm versus 0.199 [0.179-0.210] mm, P = 0.94) or femoral neck BMD T-scores (+20.7%, -2.1 [-2.8 to -1.4] versus -2.6 [-3.3 to -2.5], P = 0.24) between groups., Conclusion: The 3T MRI can potentially detect detrimental changes in proximal femur microarchitecture and strength in long-term glucocorticoid users., (© 2015 Wiley Periodicals, Inc.)

Purpose: To evaluate the within-day and between-day measurement reproducibility of in vivo 3D MRI assessment of trabecular bone microarchitecture of the proximal femur., Materials and Methods: This Health Insurance Portability and Accountability Act (HIPPA)-compliant, Institutional Review Board (IRB)-approved study was conducted on 11 healthy subjects (mean age = 57.4 ± 14.1 years) with written informed consent. All subjects underwent a 3T MRI hip scan in vivo (0.234 × 0.234 × 1.5 mm) at three timepoints: baseline, second scan same day (intrascan), and third scan 1 week later (interscan). We applied digital topological analysis and volumetric topological analysis to compute the following microarchitectural parameters within the femoral neck: total bone volume, bone volume fraction, markers of trabecular number (skeleton density), connectivity (junctions), plate-like structure (surfaces), plate width, and trabecular thickness. Reproducibility was assessed using root-mean-square coefficient of variation (RMS-CV) and intraclass correlation coefficient (ICC)., Results: The within-day RMS-CVs ranged from 2.3% to 7.8%, and the between-day RMS-CVs ranged from 4.0% to 7.3% across all parameters. The within-day ICCs ranged from 0.931 to 0.989, and the between-day ICCs ranged from 0.934 to 0.971 across all parameters., Conclusion: These results demonstrate high reproducibility for trabecular bone microarchitecture measures derived from 3T MR images of the proximal femur. The measurement reproducibility is within a range suitable for clinical cross-sectional and longitudinal studies in osteoporosis., (© 2015 Wiley Periodicals, Inc.)

Purpose: To determine how subchondral bone microarchitecture is altered in patients with mild knee osteoarthritis., Materials and Methods: This study had Institutional Review Board approval. We recruited 24 subjects with mild radiographic knee osteoarthritis and 16 healthy controls. The distal femur was scanned at 7T using a high-resolution 3D FLASH sequence. We applied digital topological analysis to assess bone volume fraction, markers of trabecular number (skeleton density), trabecular network osteoclastic resorption (erosion index), plate-like structure (surface), rod-like structure (curve), and plate-to-rod ratio (surface-curve ratio). We used two-tailed t-tests to compare differences between osteoarthritis subjects and controls., Results: 7T magnetic resonance imaging (MRI) detected deterioration in subchondral bone microarchitecture in both medial and lateral femoral condyles in osteoarthritis subjects as compared with controls. This was manifested by lower bone volume fraction (-1.03% to -5.43%, P < 0.04), higher erosion index (+8.49 to +22.76%, P < 0.04), lower surface number (-2.31% to -9.63%, P < 0.007), higher curve number (+6.85% to +16.93%, P < 0.03), and lower plate-to-rod ratio (-7.92% to -21.71%, P < 0.05)., Conclusion: The results provide further support for the concept that poor subchondral bone quality is associated with osteoarthritis and may serve as a potential therapeutic target for osteoarthritis interventions. J. Magn. Reson. Imaging 2015;41:1311-1317. © 2014 Wiley Periodicals, Inc., (© 2014 Wiley Periodicals, Inc.)

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., (© 2014 Wiley Periodicals, Inc.)

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., (© 2014 Wiley Periodicals, Inc.)

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., (© 2013 Wiley Periodicals, Inc.)

Purpose: High-resolution imaging of deeper anatomy such as the hip is challenging due to low signal-to-noise ratio (SNR), necessitating long scan times. Multi-element coils can increase SNR and reduce scan time through parallel imaging (PI). We assessed the feasibility of using a 26-element receive coil setup to perform 3 Tesla (T) MRI of proximal femur microarchitecture without and with PI., Materials and Methods: This study had institutional review board approval. We scanned 13 subjects on a 3T scanner using 26 receive-elements and a three-dimensional fast low-angle shot (FLASH) sequence without and with PI (acceleration factors [AF] 2, 3, 4). We assessed SNR, depiction of individual trabeculae, PI performance (1/g-factor), and image quality with PI (1 = nonvisualization to 5 = excellent)., Results: SNR maps demonstrate higher SNR for the 26-element setup compared with a 12-element setup for hip MRI. Without PI, individual proximal femur trabeculae were well-depicted, including microarchitectural deterioration in osteoporotic subjects. With PI, 1/g values for the 26-element/12-element receive-setup were 0.71/0.45, 0.56/0.25, and 0.44/0.08 at AF2, AF3, and AF4, respectively. Image quality was: AF1, excellent (4.8 ± 0.4); AF2, good (4.2 ± 1.0); AF3, average (3.3 ± 1.0); AF4, nonvisualization (1.4 ± 0.9)., Conclusion: A 26-element receive-setup permits 3T MRI of proximal femur microarchitecture with good image quality up to PI AF2., (© 2013 Wiley Periodicals, Inc.)

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 mm(3) ) 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 mm(3) ) 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., (Copyright © 2013 Wiley Periodicals, Inc.)

In this article we present an up-to-date overview of the potential biomedical applications of sodium magnetic resonance imaging (MRI) in vivo. Sodium MRI is a subject of increasing interest in translational imaging research as it can give some direct and quantitative biochemical information on the tissue viability, cell integrity and function, and therefore not only help the diagnosis but also the prognosis of diseases and treatment outcomes. It has already been applied in vivo in most human tissues, such as brain for stroke or tumor detection and therapeutic response, in breast cancer, in articular cartilage, in muscle, and in kidney, and it was shown in some studies that it could provide very useful new information not available through standard proton MRI. However, this technique is still very challenging due to the low detectable sodium signal in biological tissue with MRI and hardware/software limitations of the clinical scanners. The article is divided in three parts: 1) the role of sodium in biological tissues, 2) a short review on sodium magnetic resonance, and 3) a review of some studies on sodium MRI on different organs/diseases to date., (Copyright © 2013 Wiley-Liss, Inc.)

Purpose: To compare a new birdcage-transmit, 28-channel receive array (28-Ch) coil and a quadrature volume coil for 7T morphologic MRI and T2 mapping of knee cartilage., Materials and Methods: The right knees of 10 healthy subjects were imaged on a 7T whole body magnetic resonance (MR) scanner using both coils. 3D fast low-angle shot (3D-FLASH) and multiecho spin-echo (MESE) sequences were implemented. Cartilage signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), thickness, and T2 values were assessed., Results: SNR/CNR was 17%-400% greater for the 28-Ch compared to the quadrature coil (P ≤ 0.005). Bland-Altman plots show mean differences between measurements of tibial/femoral cartilage thickness and T2 values obtained with each coil to be small (-0.002 ± 0.009 cm / 0.003 ± 0.011 cm) and large (-6.8 ± 6.7 msec/-8.2 ± 9.7 msec), respectively. For the 28-Ch coil, when parallel imaging with acceleration factors (AF) 2, 3, and 4 was performed SNR retained was: 62%-69%, 51%-55%, and 39%-45%., Conclusion: A 28-Ch knee coil provides increased SNR/CNR for 7T cartilage morphologic imaging and T2 mapping. Coils should be switched with caution during clinical studies because T2 values may differ. The greater SNR of the 28-Ch coil could be used to perform parallel imaging with AF2 and obtain similar SNR as the quadrature coil., (Copyright © 2011 Wiley Periodicals, Inc.)

Purpose: To determine the feasibility of performing MRI of the wrist at 7 Tesla (T) with parallel imaging and to evaluate how acceleration factors (AF) affect signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and image quality., Materials and Methods: This study had institutional review board approval. A four-transmit eight-receive channel array coil was constructed in-house. Nine healthy subjects were scanned on a 7T whole-body MR scanner. Coronal and axial images of cartilage and trabecular bone micro-architecture (3D-Fast Low Angle Shot (FLASH) with and without fat suppression, repetition time/echo time = 20 ms/4.5 ms, flip angle = 10 degrees , 0.169-0.195 x 0.169-0.195 mm, 0.5-1 mm slice thickness) were obtained with AF 1, 2, 3, 4. T1-weighted fast spin-echo (FSE), proton density-weighted FSE, and multiple-echo data image combination (MEDIC) sequences were also performed. SNR and CNR were measured. Three musculoskeletal radiologists rated image quality. Linear correlation analysis and paired t-tests were performed., Results: At higher AF, SNR and CNR decreased linearly for cartilage, muscle, and trabecular bone (r < -0.98). At AF 4, reductions in SNR/CNR were:52%/60% (cartilage), 72%/63% (muscle), 45%/50% (trabecular bone). Radiologists scored images with AF 1 and 2 as near-excellent, AF 3 as good-to-excellent (P = 0.075), and AF 4 as average-to-good (P = 0.11)., Conclusion: It is feasible to perform high resolution 7T MRI of the wrist with parallel imaging. SNR and CNR decrease with higher AF, but image quality remains above-average.

Purpose: To demonstrate the feasibility of acquiring high-resolution, isotropic 3D-sodium magnetic resonance (MR) images of the whole knee joint in vivo at ultrahigh field strength (7.0T) via a 3D-radial acquisition with ultrashort echo times and clinically acceptable acquisition times., Materials and Methods: Five healthy controls (four males, one female; mean +/- standard deviation [SD] age 28.7 +/- 4.8 years) and five patients with osteoarthritis (OA) (three males, two females; mean +/- SD age 52.4 +/- 5.6 years) underwent (23)Na MRI on a 7T, multinuclei equipped whole-body scanner. A quadrature (23)Na knee coil and a 3D-gradient echo (GRE) imaging sequence with a radial acquisition were utilized. Cartilage sodium concentration was measured and compared between the healthy controls and OA patients., Results: The average signal-to-noise ratio (SNR) for different spatial resolutions (1.2-4 mm) varied from approximately 14-120, respectively. The mean sodium concentration of healthy subjects ranged from approximately 240 +/- 28 mM/L to 280 +/- 22 mM/L. However, in OA patients the sodium concentrations were reduced significantly by approximately 30%-60%, depending on the degree of cartilage degeneration., Conclusion: The preliminary results suggest that sodium imaging at 7T may be a feasible potential alternative for physiologic OA imaging and clinical diagnosis.

Purpose: To demonstrate the feasibility of quantitatively evaluating and measuring T(1) and T(2) relaxation times of human tibialis anterior (TA) muscles metabolites in vivo at 7T and to compare these results with those of 3T., Materials and Methods: A model lipid phantom (corn oil) and healthy volunteers (n = 4, mean +/- SD age 35.6 +/- 5.6 years) were scanned on 3T and 7T whole-body MR scanners. A voxel of 10 x 10 x 10 mm(3) was positioned on the lipid phantom and right calf TA muscles using the single-voxel stimulated echo acquisition mode (STEAM) pulse sequence. All magnetic resonance spectroscopy (MRS) data were processed with Java-based Magnetic Resonance User Interface (JMRUI) using Hankel Lanczos Singular Value Decomposition (HLSVD) filtering to remove the residual water signal., Results: T(1) shows a steady increase while T(2) shows a slight decrease with B(0) and the spectra show larger spectral resolution at 7T than at 3T in the lipid phantom. T(1) values of all the metabolites are higher, while T(2) values are slightly lower at 7T than those of 3T compared to reported results in TA. The maximum percentage of increase in T(1) is about approximately 488%, the maximum percentage of decrease in T(2) is about approximately 65%., Conclusion: The preliminary results can potentially be used for calculating relaxation correction factors required for absolute quantitation of skeletal muscle metabolite concentrations and for further protocol and sequence optimization.

Purpose: To produce in vivo high-resolution images of the knee and to determine the feasibility of using 7T MR to detect changes in trabecular bone microarchitecture in elite athletes (Olympic fencers) who undergo high impact activity., Materials and Methods: The dominant knees of four males from the U.S. Olympic Fencing Team and three matched healthy male controls were scanned in a 7T whole-body scanner using a quadrature knee coil with three-dimensional (3D) fast low angle shot (FLASH): 50 axial images at the distal femur (0.156 mm x 0.156 mm) and 80 axial images at the knee joint (0.195 mm x 0.195 mm). Bone volume fraction (BVF) and marrow volume fraction (MVF) images were computed and fuzzy distance transform (FDT) and digital topological analysis (DTA) were applied to determine: trabecular number (Tb.N), trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp); BVF (BV/TV); trabecular and marrow space surface-to-curve ratio (SC, marker of plate to rod ratio); and trabecular and marrow space erosion index (EI, inverse marker for network connectivity). Quadriceps muscle volume (MV) was calculated as well. We calculated group means and performed two-tailed t-tests to determine statistical significance., Results: Compared to controls, fencers had: decreased Tb.Sp (P = 0.0082 at femur, P = 0.051 at joint); increased Tb.N (P < 0.05 at both femur and joint) and BV/TV (P < 0.001 at both femur and joint); increased trabecular SC and decreased marrow space SC (P < 0.01 at both femur and joint); decreased trabecular EI and increased marrow space EI (P < 0.01 at both femur and joint); and increased MV (P = 0.038). There was no difference in Tb.Th at the distal femur (P = 0.92) or joint (P = 0.71) between groups., Conclusion: To our knowledge, this is the first study to perform 7T MRI of the knee in vivo. Elite athletes who undergo high impact activity have increased MV and improved trabecular bone structure compared to controls., ((c) 2008 Wiley-Liss, Inc.)

Purpose: To rapidly acquire T(1)-weighted images using a three-dimensional fast low angle shot (3D FLASH) sequence in combination with generalized autocalibrating partially parallel acquisitions (GRAPPA) and variable flip angle (VFA) method at 3.0T., Materials and Methods: 3D T(1) maps of model systems (gadolinium [Gd] and agarose phantoms), bovine cartilage, and human subjects were constructed on a 3.0T clinical whole-body MR scanner. The T(1) values of model systems measured using the 2D inversion-recovery fast-spin-echo (IR-FSE) sequence were considered as a reference method to validate the rapid 3D method for comparison., Results: The root mean square coefficient of variation percentage (RMS-CV%) of the median T(1) of agarose phantom across different acquisition methods was approximately 6.2%. The RMS-CV% of the median T(1) of bovine cartilage across different acquisition methods was approximately 4.1%. The RMS-CV% of median T(1) of the cartilages among the subjects was between approximately 7.3% to 11.1%. In our study, rapid 3D-T(1) mapping with VFA and parallel imaging with different acceleration factors (AFs) (AF = 1, 2, 3, and 4) seems to have no obvious influence on the T(1) mapping (before and after contrast agent administration)., Conclusion: The preliminary results demonstrate that it is possible to quantify 3D-T(1) mapping of the whole knee joint (with 0.7 mm(3) isotropic resolution) under approximately five minutes with excellent in vivo reproducibility at 3.0T.

High-field (3T) and ultra-high-field (UHF, 7T and above) systems are increasingly being used to explore potential musculoskeletal applications because they provide a high intrinsic signal-to-noise ratio (SNR), potentially higher resolution (spatial and temporal), and improved contrast. However, imaging at 7T and above presents certain challenges, such as homogeneous radiofrequency (RF) coil design, increased chemical shift artifacts, susceptibility artifacts, RF energy deposition, and changes in relaxation times compared to more typical clinical scanners (1.5 and 3T). Despite these issues, MRI at 7T likely will provide some excellent opportunities for high-resolution morphologic imaging and forays into functional imaging of musculoskeletal systems. In this review we address some of these issues and also demonstrate the feasibility of acquiring high-resolution in vivo images of the musculoskeletal system in healthy human volunteers at 7.0T., ((c) 2007 Wiley-Liss, Inc.)

Purpose: To demonstrate the feasibility of three-dimensional (3D) T(1rho)-weighted imaging of human knee joint at 3.0T without exceeding the specific absorption rate (SAR) limits and the measurement of the baseline T(1rho) values of patellar cartilage and several muscles at the knee joint., Materials and Methods: 3D gradient-echo sequence with a self-compensating spin-lock pulse cluster of 250 Hz power was used to acquire 3D-T(1rho)-weighted images of the knee joint of five healthy subjects. Global and regional analysis of patellar cartilage T(1rho) were performed. Furthermore, T(1rho) of several periarticular muscles were analyzed., Results: The global average T(1rho) value of the patellar cartilage varied from 39 to 43 msec. The regional average T(1rho) values varied from 38 to 42 msec, and from 42 to 44 msec for medial and lateral facets, respectively. In vivo reproducibility of average T(1rho) of patellar cartilage was found to be 5% (coefficient of variation). Similarly, the global average T(1rho) values for biceps femoris, lateral gastrocnemius, medial gastrocnemius, and sartorius varied between 31-46, 29-49, 35-48, and 32-50 msec, respectively., Conclusion: We demonstrated the feasibility of 3D-T(1rho)-weighted imaging of the knee joint at 3.0T without exceeding SAR limits., ((c) 2006 Wiley-Liss, Inc.)

Purpose: To quantify the spin-lattice relaxation time in the rotating frame (T1rho) in various clinical grades of human osteoarthritis (OA) cartilage specimens obtained from total knee replacement surgery, and to correlate the T1rho with OA disease progression and compare it with the transverse relaxation time (T2)., Materials and Methods: Human cartilage specimens were obtained from consenting patients (N = 8) who underwent total replacement of the knee joint at the Pennsylvania Hospital, Philadelphia, PA, USA. T2- and T1rho-weighted images were obtained on a 4.0 Tesla whole-body GE Signa scanner (GEMS, Milwaukee, WI, USA). A 7-cm diameter transmit/receive quadrature birdcage coil tuned to 170 MHz was employed., Results: All of the surgical knee replacement OA cartilage specimens showed elevated relaxation times (T2 and T1rho) compared to healthy cartilage tissue. In various grades of OA specimens, the T1rho relaxation times varied from 62 +/- 5 msec to 100 +/- 8 msec (mean +/- SEM) depending on the degree of cartilage degeneration. However, T2 relaxation times varied only from 32 +/- 2 msec to 45 +/- 4 msec (mean +/- SEM) on the same cartilage specimens. The increase in T2 and T1rho in various clinical grades of OA specimens were approximately 5-50% and 30-120%, respectively, compared to healthy specimens. The degenerative status of the cartilage specimens was also confirmed by histological evaluation., Conclusion: Preliminary results from a limited number of knee specimens (N = 8) suggest that T1rho relaxation mapping is a sensitive noninvasive marker for quantitatively predicting and monitoring the status of macromolecules in early OA. Furthermore, T1rho has a higher dynamic range (>100%) for detecting early pathology compared to T2. This higher dynamic range can be exploited to measure even small macromolecular changes with greater accuracy compared to T2. Because of these advantages, T1rho relaxation mapping may be useful for evaluating early OA therapy., (2006 Wiley-Liss, Inc.)

Purpose: To measure the proton magnetization transfer ratio (MTR) maps in control and collagen-depleted bovine patellar cartilage specimens as a function of cartilage depth during mechanical compression., Materials and Methods: One-dimensional proton projection MR images employing a spin-echo imaging sequence were obtained on a custom-built NMR spectrometer interfaced to an Oxford magnet operating at 2T. The mechanical compressions were performed with a custom-built MR-compatible pressure cell and evaluated dynamically via one-dimensional projection. High-spatial-resolution two-dimensional MT images were obtained using a fast spin-echo (FSE) sequence on a 4T whole-body GE Signa scanner (GEMS, Milwaukee, WI, USA) to quantify the MTR maps of normal and collagen-depleted bovine patellae., Results: All of the cartilage plugs from the bovine patellae showed that the MTR value increases continuously as a function of cartilage depth. Although the overall MTR trend as a function of depth is the same in both control and collagen-depleted cartilage, the magnitude of the MTR value differs between the two. The MTR value is decreased with collagen depletion and increased with mechanical compression. The increase in MTR value during compression may be due to a decrease in free water content and volume, resulting in an increase in collagen concentration., Conclusion: We demonstrated that the MTR in bovine patellar cartilage is depth-dependent and is relatively higher in the radial zone compared to the superficial zone. The high MTR in the radial zone not only depends on collagen content, it may also reflect a number of other parameters, such as the arrangement of macromolecules, high solid content, bound water fraction attached to macromolecules, radial orientation, etc., ((c) 2005 Wiley-Liss, Inc.)

Purpose: To measure T1rho relaxation times and T1rho dispersion in the human brain in vivo., Materials and Methods: Magnetic resonance imaging (MRI) was performed on a 1.5-T GE Signa clinical scanner using the standard GE head coil. A fast spin-echo (FSE)-based T1rho-weighted MR pulse sequence was employed to obtain images from five healthy male volunteers. Optimal imaging parameters were determined while considering both the objective of the study and the guarantee that radio-frequency (RF) power deposition during MR did not exceed Food and Drug Administration (FDA)-mandated safety levels., Results: T1rho-weighted MR images showed excellent contrast between different brain tissues. These images were less blurred than corresponding T2-weighted images obtained with similar contrast, especially in regions between brain parenchyma and cerebrospinal fluid (CSF). Average T1rho values for white matter (WM), gray matter (GM), and CSF were 85 +/- 3, 99 +/- 1, and 637 +/- 78 msec, respectively, at a spin-locking field of 500 Hz. T1rho is 30% higher in the parenchyma and 78% higher in CSF compared to the corresponding T2 values. T1rho dispersion was observed between spin-locking frequencies 0 and 500 Hz., Conclusion: T1rho-weighted MRI provides images of the brain with superb contrast and detail. T1rho values measured in the different brain tissues will serve as useful baseline values for analysis of T1rho changes associated with pathology., (Copyright 2004 Wiley-Liss, Inc.)

Purpose: To design and implement a magnetic resonance imaging (MRI) pulse sequence capable of performing three-dimensional T(1rho)-weighted MRI on a 1.5-T clinical scanner, and determine the optimal sequence parameters, both theoretically and experimentally, so that the energy deposition by the radiofrequency pulses in the sequence, measured as the specific absorption rate (SAR), does not exceed safety guidelines for imaging human subjects., Materials and Methods: A three-pulse cluster was pre-encoded to a three-dimensional gradient-echo imaging sequence to create a three-dimensional, T(1rho)-weighted MRI pulse sequence. Imaging experiments were performed on a GE clinical scanner with a custom-built knee-coil. We validated the performance of this sequence by imaging articular cartilage of a bovine patella and comparing T(1rho) values measured by this sequence to those obtained with a previously tested two-dimensional imaging sequence. Using a previously developed model for SAR calculation, the imaging parameters were adjusted such that the energy deposition by the radiofrequency pulses in the sequence did not exceed safety guidelines for imaging human subjects. The actual temperature increase due to the sequence was measured in a phantom by a MRI-based temperature mapping technique. Following these experiments, the performance of this sequence was demonstrated in vivo by obtaining T(1rho)-weighted images of the knee joint of a healthy individual., Results: Calculated T(1rho) of articular cartilage in the specimen was similar for both and three-dimensional and two-dimensional methods (84 +/- 2 msec and 80 +/- 3 msec, respectively). The temperature increase in the phantom resulting from the sequence was 0.015 degrees C, which is well below the established safety guidelines. Images of the human knee joint in vivo demonstrate a clear delineation of cartilage from surrounding tissues., Conclusion: We developed and implemented a three-dimensional T(1rho)-weighted pulse sequence on a 1.5-T clinical scanner., (Copyright 2003 Wiley-Liss, Inc.)