Quantification of cartilage biomechanical and biochemical properties via T1rho magnetic resonance imaging

Quantitative and Compositional MRI of the Articular Cartilage: A Narrative Review

This review examines the latest advancements in compositional and quantitative cartilage MRI techniques, addressing both their potential and challenges. The integration of these advancements promises to improve disease detection, treatment monitoring, and overall patient care. We want to highlight the pivotal task of translating these techniques into widespread clinical use, the transition of cartilage MRI from technical validation to clinical application, emphasizing its critical role in identifying early signs of degenerative and inflammatory joint diseases. Recognizing these changes early may enable informed treatment decisions, thereby facilitating personalized medicine approaches. The evolving landscape of cartilage MRI underscores its increasing importance in clinical practice, offering valuable insights for patient management and therapeutic interventions. This review aims to discuss the old evidence and new insights about the evaluation of articular cartilage through MRI, with an update on the most recent literature published on novel quantitative sequences.

Quantitative MRI methods for the assessment of structure, composition, and function of musculoskeletal tissues in basic research and preclinical applications

Osteoarthritis (OA) is a disabling chronic disease involving the gradual degradation of joint structures causing pain and dysfunction. Magnetic resonance imaging (MRI) has been widely used as a non-invasive tool for assessing OA-related changes. While anatomical MRI is limited to the morphological assessment of the joint structures, quantitative MRI (qMRI) allows for the measurement of biophysical properties of the tissues at the molecular level. Quantitative MRI techniques have been employed to characterize tissues' structural integrity, biochemical content, and mechanical properties. Their applications extend to studying degenerative alterations, early OA detection, and evaluating therapeutic intervention. This article is a review of qMRI techniques for musculoskeletal tissue evaluation, with a particular emphasis on articular cartilage. The goal is to describe the underlying mechanism and primary limitations of the qMRI parameters, their association with the tissue physiological properties and their potential in detecting tissue degeneration leading to the development of OA with a primary focus on basic and preclinical research studies. Additionally, the review highlights some clinical applications of qMRI, discussing the role of texture-based radiomics and machine learning in advancing OA research.

Nucleus pulposus structure and function assessed in shear using magnetic resonance elastography, quantitative MRI, and rheometry

Background

In vivo quantification of the structure-function relationship of the intervertebral disc (IVD) via quantitative MRI has the potential to aid objective stratification of disease and evaluation of restorative therapies. Magnetic resonance elastography (MRE) is an imaging technique that assesses tissue shear properties and combined with quantitative MRI metrics reflective of composition can inform structure-function of the IVD. The objectives of this study were to (1) compare MRE- and rheometry-derived shear modulus in agarose gels and nucleus pulposus (NP) tissue and (2) correlate MRE and rheological measures of NP tissue with composition and quantitative MRI.

Method

MRE and MRI assessment (i.e., T1ρ and T2 mapping) of agarose samples (2%, 3%, and 4% (w/v); n = 3-4/%) and of bovine caudal IVDs after equilibrium dialysis in 5% or 25% PEG (n = 13/PEG%) was conducted. Subsequently, agarose and NP tissue underwent torsional mechanical testing consisting of a frequency sweep from 1 to 100 Hz at a rotational strain of 0.05%. NP tissue was additionally evaluated under creep and stress relaxation conditions. Linear mixed-effects models and univariate regression analyses evaluated the effects of testing method, %agarose or %PEG, and frequency, as well as correlations between parameters.

Results

MRE- and rheometry-derived shear moduli were greater at 100 Hz than at 80 Hz in all agarose and NP tissue samples. Additionally, all samples with lower water content had higher complex shear moduli. There was a significant correlation between MRE- and rheometry-derived modulus values for homogenous agarose samples. T1ρ and T2 relaxation times for agarose and tissue were negatively correlated with complex shear modulus derived from both techniques. For NP tissue, shear modulus was positively correlated with GAG/wet-weight and negatively correlated with %water content.

Conclusion

This work demonstrates that MRE can assess hydration-induced changes in IVD shear properties and further highlights the structure-function relationship between composition and shear mechanical behaviors of NP tissue.

Tibial and femoral articular cartilage exhibit opposite outcomes for T1ρ and T2* relaxation times in response to acute compressive loading in healthy knees

Abnormal loading is thought to play a key role in the disease progression of cartilage, but our understanding of how cartilage compositional measurements respond to acute compressive loading in-vivo is limited. Ten healthy subjects were scanned at two timepoints (7 ± 3 days apart) with a 3 T magnetic resonance imaging (MRI) scanner. Scanning sessions included T1ρ and T2* acquisitions of each knee in two conditions: unloaded (traditional MRI setup) and loaded in compression at 40 % bodyweight as applied by an MRI-compatible loading device. T1ρ and T2* parameters were quantified for contacting cartilage (tibial and femoral) and non-contacting cartilage (posterior femoral condyle) regions. Significant effects of load were found in contacting regions for both T1ρ and T2*. The effect of load (loaded minus unloaded) in femoral contacting regions ranged from 4.1 to 6.9 ms for T1ρ, and 3.5 to 13.7 ms for T2*, whereas tibial contacting regions ranged from -5.6 to -1.7 ms for T1ρ, and -2.1 to 0.7 ms for T2*. Notably, the responses to load in the femoral and tibial cartilage revealed opposite effects. No significant differences were found in response to load between the two visits. This is the first study that analyzed the effects of acute loading on T1ρ and T2* measurements in human femoral and tibial cartilage separately. The results suggest the effect of acute compressive loading on T1ρ and T2* was: 1) opposite in the femoral and tibial cartilage; 2) larger in contacting regions than in non-contacting regions of the femoral cartilage; and 3) not different visit-to-visit.

T1rho MR properties of human patellar cartilage: correlation with indentation stiffness and biochemical contents

OBJECTIVE

Cartilage degeneration involves structural, compositional, and biomechanical alterations that may be detected non-invasively using quantitative MRI. The goal of this study was to determine if topographical variation in T1rho values correlates with indentation stiffness and biochemical contents of human patellar cartilage.

DESIGN

Cadaveric patellae from unilateral knees of 5 donors with moderate degeneration were imaged at 3-Telsa with spiral chopped magnetization preparation T1rho sequence. Indentation testing was performed, followed by biochemical analyses to determine water and sulfated glycosaminoglycan contents. T1rho values were compared to indentation stiffness, using semi-circular regions of interest (ROIs) of varying sizes at each indentation site. ROIs matching the resected tissues were analyzed, and univariate and multivariate regression analyses were performed to compare T1rho values to biochemical contents.

RESULTS

Grossly, superficial degenerative change of the cartilage (i.e., roughened texture and erosion) corresponded with regions of high T1rho values. High T1rho values correlated with low indentation stiffness, and the strength of correlation varied slightly with the ROI size. Spatial variations in T1rho values correlated positively with that of the water content (R2 = 0.10, p < 0.05) and negatively with the variations in the GAG content (R2 = 0.13, p < 0.01). Multivariate correlation (R2 = 0.23, p < 0.01) was stronger than either of the univariate correlations.

CONCLUSION

These results demonstrate the sensitivity of T1rho values to spatially varying function and composition of cartilage and that the strength of correlation depends on the method of data analysis and consideration of multiple variables.

Impact of hyaluronic acid injection on the knee joint friction

PURPOSE

The purpose of this in vitro study was to investigate whether or not hyaluronic acid supplementation improves knee joint friction during osteoarthritis progression under gait-like loading conditions.

METHODS

Twelve human cadaveric knee joints were equally divided into mild and moderate osteoarthritic groups. After initial conservative preparation, a passive pendulum setup was used to test the whole joints under gait-like conditions before and after hyaluronic acid supplementation. The friction-related damping properties given by the coefficient of friction µ and the damping coefficient c (in kg m2/s) were calculated from the decaying flexion-extension motion of the knee. Subsequently, tibial and femoral cartilage and meniscus samples were extracted from the joints and tested in an established dynamic pin-on-plate tribometer using synthetic synovial fluid followed by synthetic synovial fluid supplemented with hyaluronic acid as lubricant. Friction was quantified by calculating the coefficient of friction.

RESULTS

In the pendulum tests, the moderate OA group indicated significantly lower c0 values (p < 0.05) under stance phase conditions and significantly lower µ0 (p = 0.01) values under swing phase conditions. No degeneration-related statistical differences were found for µend or cend. Friction was not significantly different (p > 0.05) with regard to mild and moderate osteoarthritis in the pin-on-plate tests. Additionally, hyaluronic acid did not affect friction in both, the pendulum (p > 0.05) and pin-on-plate friction tests (p > 0.05).

CONCLUSION

The results of this in vitro study suggested that the friction of cadaveric knee joint tissues does not increase with progressing degeneration. Moreover, hyaluronic acid viscosupplementation does not lead to an initial decrease in knee joint friction.

3D T1rho sequences with FASE, UTE, and MAPSS acquisitions for knee evaluation

PURPOSE

For biochemical evaluation of soft tissues of the knee, T1rho magnetic resonance imaging (MRI) has been proposed. Purpose of this study was to compare three T1rho sequences based on fast advanced spin echo (FASE), ultrashort echo time (UTE), and magnetization-prepared angle-modulated partitioned k-space spoiled gradient echo snapshots (MAPSS) acquisitions for the knee evaluation.

MATERIALS AND METHODS

We developed two T1rho sequences using 3D FASE or 3D radial UTE acquisitions. 3D MAPSS T1rho was provided by the manufacturer. Agarose phantoms with varying concentrations were imaged. Additionally, bilateral knees of asymptomatic subjects were imaged sagittally. T1rho values of the phantoms and 4 regions of interest (ROI) of the knees (i.e., anterior and posterior meniscus, femoral and tibial cartilage) were determined.

RESULTS

In phantoms, all T1rho values monotonically decreased with increasing agarose concentration. 3D MAPSS T1rho values of 51, 34, and 38 ms were found for 2, 3, and 4% agarose, respectively, similar to published values on another platform. In the knee, the raw images were detailed with good contrast. Cartilage and meniscus T1rho values varied with the pulse sequence, being the lowest in the 3D UTE T1rho sequence. Comparing different ROIs, menisci generally had lower T1rho values compared to cartilage, as expected in healthy knees.

CONCLUSION

We have successfully developed and implemented the new T1rho sequences and validated them using agarose phantoms and volunteer knees. All sequences were optimized to be clinically feasible (~ 5 min or less) and yielded satisfactory image quality and T1rho values consistent with the literature.

Age-Dependent Changes in Knee Cartilage T1 , T2 , and T1p Simultaneously Measured Using MRI Fingerprinting

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.

Integrating MR imaging with full-surface indentation mapping of femoral cartilage in an ex vivo porcine stifle

The potential of MRI to predict cartilage mechanical properties across an entire cartilage surface in an ex vivo model would enable novel perspectives in modeling cartilage tolerance and predicting disease progression. The purpose of this study was to integrate MR imaging with full-surface indentation mapping to determine the relationship between femoral cartilage thickness and T2 relaxation change following loading, and cartilage mechanical properties in an ex vivo porcine stifle model. Matched-pairs of stifle joints from the same pig were randomized into either 1) an imaging protocol where stifles were imaged at baseline and after 35 min of static axial loading; and 2) full surface mapping of the instantaneous modulus (IM) and an electromechanical property named quantitative parameter (QP). The femur and femoral cartilage were segmented from baseline and post-intervention scans, then meshes were generated. Coordinate locations of the indentation mapping points were rigidly registered to the femur. Multiple linear regressions were performed at each voxel testing the relationship between cartilage outcomes (thickness change, T2 change) and mechanical properties (IM, QP) after accounting for covariates. Statistical Parametric Mapping was used to determine significance of clusters. No significant clusters were identified; however, this integrative method shows promise for future work in ex vivo modeling by identifying spatial relationships among variables.

Possibility for Visualizing the Muscle Microstructure by q-Space Imaging Technique

In the human body, skeletal muscle microstructures have been evaluated only by biopsy. Noninvasive examination of the microstructure of muscles would be useful for research and clinical practice in sports and musculoskeletal areas. The study is aimed at determining if q-space imaging (QSI) can reveal the microstructure of muscles in humans. Forty-three Japanese subjects (controls, distance runners, powerlifting athletes, and teenage runners) were included in this cross-sectional study. Magnetic resonance imaging of the lower leg was performed. On each leg muscle, full width at half maximum (FWHM) which indicated the muscle cell diameters and pennation angle (PA) were measured and compared. FWHM showed significant positive correlations with PA, which is related to muscle strength. In addition, FWHM was higher for powerlifting, control, distance running, and teenager, in that order, suggesting that it may be directing the diameter of each muscle cell. Type 1 and type 2 fibers are enlarged by growth, so the fact that the FWHM of the control group was larger than that of the teenagers in this study may indicate that the muscle fibers were enlarged by growth. Also, FWHM has the possibility to increase with increased muscle fibers caused by training. We showed that QSI had the possibility to depict noninvasively the microstructure like muscle fiber type and subtle changes caused by growth and sports characteristics, which previously could only be assessed by biopsy.

Time-Dependent Change in Cartilage Repair Tissue Evaluated by Magnetic Resonance Imaging up to 2 years after Atelocollagen-Assisted Autologous Cartilage Transplantation: Data from the CaTCh Study

OBJECTIVE

To elucidate the time course of magnetic resonance imaging (MRI)-based morphological and qualitative outcomes after an atelocollagen-assisted autologous chondrocyte implantation (ACI) and to analyze the correlation between arthroscopic and MRI-based assessment.

DESIGN

We included ACI recipients from a multicenter registration study (CaTCh [Cartilage Treatment in Chiba] study). Morphological (3-dimensional magnetic resonance observation of cartilage repair tissue: 3D-MOCART, MOCART2.0) and qualitative assessment (T2- and T1rho-mapping) by MRI were conducted at 6, 12, and 24 months post-implantation. Global T2 and T1rho indices (T2 and T1rho in repair tissue divided by T2 and T1rho in normal cartilage) were calculated. Arthroscopic second-look assessment was performed in 4 and 15 knees at 12 and 24 months post-implantation, respectively.

RESULTS

The 3D-MOCART over 12 months witnessed significant patient improvement, but some presented subchondral bone degeneration as early as 6 months. The MOCART2.0 improved from 57.5 to 71.3 between 6 and 24 months (P = 0.02). The global T2 index decreased from 1.7 to 1.2 between 6 and 24 months (P < 0.001). The global T1rho index decreased from 1.5 to 1.3 between 6 and 24 months (P = 0.004). Normal or nearly normal ICRS-CRA (cartilage repair assessment scale developed by the International Cartilage Repair Society) grades were achieved in 86% and 93% of the lesions at 12 and 24 months, respectively. Better ICRS-CRA grade corresponded to better MOCART2.0, with no trend in the T2 and T1rho values.

CONCLUSIONS

Atelocollagen-assisted ACI improved the MRI-based morphological and qualitative outcomes until 24 months post-surgery, and normal or nearly normal grades were achieved in most lesions by arthroscopic assessment. MRI assessment may be an alternative to arthroscopic assessment.

Imaging in Osteoarthritis

Osteoarthritis (OA) is the most frequent form of arthritis with major implications on both individual and public health care levels. The field of joint imaging, and particularly magnetic resonance imaging (MRI), has evolved rapidly due to the application of technical advances to the field of clinical research. This narrative review will provide an introduction to the different aspects of OA imaging aimed at an audience of scientists, clinicians, students, industry employees, and others who are interested in OA but who do not necessarily focus on OA. The current role of radiography and recent advances in measuring joint space width will be discussed. The status of cartilage morphology assessment and evaluation of cartilage biochemical composition will be presented. Advances in quantitative three-dimensional morphologic cartilage assessment and semi-quantitative whole-organ assessment of OA will be reviewed. Although MRI has evolved as the most important imaging method used in OA research, other modalities such as ultrasound, computed tomography, and metabolic imaging play a complementary role and will also be discussed.

Acute changes in knee cartilage and meniscus following long-distance running in habituate runners: a systematic review on studies using quantitative magnetic resonance imaging

OBJECTIVE

Running is among the most popular recreational activities; nonetheless, the acute post-race changes of cartilage or meniscus have rarely been determined. The current study aimed to review the acute changes in knee cartilage and meniscus among habituate runners following long-distance running detected by using quantitative magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Systematic literature search was performed on those dominate clinical databases which including MEDLINE, Cochrane, Embase, ScienceDirect, and Web of Science. Included studies should be conducted on healthy marathon runners, and the participants should be examined before and after running by using MRI. Intervention studies were excluded.

RESULTS

A total number of 14 studies were finally included in this review which all examined the cartilage or meniscus by using MRI functional sequences. Among them, six studies quantitatively measured the changes regarding volume of the knee cartilage or/and meniscus. Five studies found that the volume would decrease initially after running. Ten studies reported T2 (T2*) would decrease after running and returned to the baseline in a short term, while T1ρ may remain increased in months. Five studies measured subareas for T2 (T2*) value, and found that the superficial and medial subarea changed more vastly than other regions after running.

CONCLUSION

Runners experience transient changes in the volume and signals of knee cartilage and meniscus after long-distance running. A liquid exchange and material interaction in cartilage and meniscus was observed after running. Superficial and medial areas of knee cartilage and meniscus might be more susceptible to mechanical loading.

Runx1 Messenger RNA Delivered by Polyplex Nanomicelles Alleviate Spinal Disc Hydration Loss in a Rat Disc Degeneration Model

Vertebral disc degenerative disease (DDD) affects millions of people worldwide and is a critical factor leading to low back and neck pain and consequent disability. Currently, no strategy has addressed curing DDD from fundamental aspects, because the pathological mechanism leading to DDD is still controversial. One possible mechanism points to the homeostatic status of extracellular matrix (ECM) anabolism, and catabolism in the disc may play a vital role in the disease’s progression. If the damaged disc receives an abundant amount of cartilage, anabolic factors may stimulate the residual cells in the damaged disc to secrete the ECM and mitigate the degeneration process. To examine this hypothesis, a cartilage anabolic factor, Runx1, was expressed by mRNA through a sophisticated polyamine-based PEG-polyplex nanomicelle delivery system in the damaged disc in a rat model. The mRNA medicine and polyamine carrier have favorable safety characteristics and biocompatibility for regenerative medicine. The endocytosis of mRNA-loaded polyplex nanomicelles in vitro, mRNA delivery efficacy, hydration content, disc shrinkage, and ECM in the disc in vivo were also examined. The data revealed that the mRNA-loaded polyplex nanomicelle was promptly engulfed by cellular late endosome, then spread into the cytosol homogeneously at a rate of less than 20 min post-administration of the mRNA medicine. The mRNA expression persisted for at least 6-days post-injection in vivo. Furthermore, the Runx1 mRNA delivered by polyplex nanomicelles increased hydration content by ≈43% in the punctured disc at 4-weeks post-injection (wpi) compared with naked Runx1 mRNA administration. Meanwhile, the disc space and ECM production were also significantly ameliorated in the polyplex nanomicelle group. This study demonstrated that anabolic factor administration by polyplex nanomicelle-protected mRNA medicine, such as Runx1, plays a key role in alleviating the progress of DDD, which is an imbalance scenario of disc metabolism. This platform could be further developed as a promising strategy applied to regenerative medicine.

Assessment of mechanical properties of articular cartilage with quantitative three-dimensional ultrashort echo time (UTE) cones magnetic resonance imaging

Conventional magnetic resonance imaging (MRI) is not capable of detecting signal from the deep cartilage due to its short transverse relaxation time (T2). Moreover, several quantitative MRI techniques are significantly influenced by the magic angle effect. The combinations of ultrashort echo time (UTE) MRI with magnetization transfer (UTE-MT) and Adiabatic T_1ρ (UTE-AdiabT_1ρ) imaging allow magic angle-insensitive assessments of all regions of articular cartilage. The purpose of this study was to investigate the correlations between quantitative three-dimensional UTE MRI biomarkers and mechanical properties of human tibiofemoral cartilage specimens. In total, 40 human tibiofemoral cartilage specimens were harvested from three male and four female donors (64 ± 18 years old). Cartilage samples were scanned using a series of quantitative 3D UTE Cones T₂* (UTE-T₂*), T₁ (UTE-T₁), UTE-AdiabT_1ρ, and UTE-MT sequences in a standard knee coil on a clinical 3T scanner. UTE-MT data were acquired with a series of MT powers and frequency offsets to calculate magnetization transfer ratio (MTR), as well as macromolecular fraction (MMF) and macromolecular T₂ (T₂mm) through modeling. Cartilage stiffness and Hayes elastic modulus were measured using indentation tests. Correlations of 3D UTE Cones MRI measurements in the superficial layer, deep layer, and global regions of interest (ROIs) with mechanical properties were investigated. Cartilage mechanical properties demonstrated highest correlations with UTE measures of the superficial layer of cartilage. AdiabT_1ρ, MTR, and MMF in superficial layer ROIs showed significant correlations with Hayes elastic modulus (p < 0.05, R = -0.54, 0.49, and 0.66, respectively). These UTE measures in global ROIs showed significant, though slightly lower, correlations with Hayes elastic modulus (p < 0.05, R = -0.37, 0.52, and 0.60, respectively). Correlations between other UTE MRI measurements (T₂*, T₁, and T₂mm) and mechanical properties were non-significant. The 3D UTE-AdiabT_1ρ and UTE-MT sequences were highlighted as promising surrogates for non-invasive assessment of cartilage mechanical properties. MMF from UTE-MT modeling showed the highest correlations with cartilage mechanics.

Direct Validation of Human Knee-Joint Contact Mechanics Derived From Subject-Specific Finite-Element Models of the Tibiofemoral and Patellofemoral Joints

The primary aim of this study was to validate predictions of human knee-joint contact mechanics (specifically, contact pressure, contact area, and contact force) derived from finite-element models of the tibiofemoral and patellofemoral joints against corresponding measurements obtained in vitro during simulated weight-bearing activity. A secondary aim was to perform sensitivity analyses of the model calculations to identify those parameters that most significantly affect model predictions of joint contact pressure, area, and force. Joint pressures in the medial and lateral compartments of the tibiofemoral and patellofemoral joints were measured in vitro during two simulated weight-bearing activities: stair descent and squatting. Model-predicted joint contact pressure distribution maps were consistent with those obtained from experiment. Normalized root-mean-square errors between the measured and calculated contact variables were on the order of 15%. Pearson correlations between the time histories of model-predicted and measured contact variables were generally above 0.8. Mean errors in the calculated center-of-pressure locations were 3.1 mm for the tibiofemoral joint and 2.1 mm for the patellofemoral joint. Model predictions of joint contact mechanics were most sensitive to changes in the material properties and geometry of the meniscus and cartilage, particularly estimates of peak contact pressure. The validated finite element modeling framework offers a useful tool for noninvasive determination of knee-joint contact mechanics during dynamic activity under physiological loading conditions.

Topographical Variation of Human Femoral Articular Cartilage Thickness, T1rho and T2 Relaxation Times Is Related to Local Loading during Walking

OBJECTIVE

Early detection of degenerative changes in the cartilage matrix composition is essential for evaluating early interventions that slow down osteoarthritis (OA) initiation. T1rho and T2 relaxation times were found to be effective for detecting early changes in proteoglycan and collagen content. To use these magnetic resonance imaging (MRI) methods, it is important to document the topographical variation in cartilage thickness, T1rho and T2 relaxation times in a healthy population. As OA is partially mechanically driven, the relation between these MRI-based parameters and localized mechanical loading during walking was investigated.

DESIGN

MR images were acquired in 14 healthy adults and cartilage thickness and T1rho and T2 relaxation times were determined. Experimental gait data was collected and processed using musculoskeletal modeling to identify weight-bearing zones and estimate the contact force impulse during gait. Variation of the cartilage properties (i.e., thickness, T1rho, and T2) over the femoral cartilage was analyzed and compared between the weight-bearing and non-weight-bearing zone of the medial and lateral condyle as well as the trochlea.

RESULTS

Medial condyle cartilage thickness was correlated to the contact force impulse ( r = 0.78). Lower T1rho, indicating increased proteoglycan content, was found in the medial weight-bearing zone. T2 was higher in all weight-bearing zones compared with the non-weight-bearing zones, indicating lower relative collagen content.

CONCLUSIONS

The current results suggest that medial condyle cartilage is adapted as a long-term protective response to localized loading during a frequently performed task and that the weight-bearing zone of the medial condyle has superior weight bearing capacities compared with the non-weight-bearing zones.

T1ρ-based fibril-reinforced poroviscoelastic constitutive relation of human articular cartilage using inverse finite element technology

Background

Mapping of T_1ρ relaxation time is a quantitative magnetic resonance (MR) method and is frequently used for analyzing microstructural and compositional changes in cartilage tissues. However, there is still a lack of study investigating the link between T_1ρ relaxation time and a feasible constitutive relation of cartilage which can be used to model complicated mechanical behaviors of cartilage accurately and properly.

Methods

Three-dimensional finite element (FE) models of ten in vitro human tibial cartilage samples were reconstructed such that each element was assigned by material-level parameters, which were determined by a corresponding T_1ρ value from MR maps. A T_1ρ-based fibril-reinforced poroviscoelastic (FRPE) constitutive relation for human cartilage was developed through an inverse FE optimization technique between the experimental and simulated indentations.

Results

A two-parameter exponential relationship was obtained between the T_1ρ and the volume fraction of the hydrated solid matrix in the T_1ρ-based FRPE constitutive relation. Compared with the common FRPE constitutive relation (i.e., without T_1ρ), the T_1ρ-based FRPE constitutive relation indicated similar indentation depth results but revealed some different local changes of the stress distribution in cartilages.

Conclusions

Our results suggested that the T_1ρ-based FRPE constitutive relation may improve the detection of changes in the heterogeneous, anisotropic, and nonlinear mechanical properties of human cartilage tissues associated with joint pathologies such as osteoarthritis (OA). Incorporating T_1ρ relaxation time will provide a more precise assessment of human cartilage based on the individual in vivo MR quantification.

Cartilage-on-cartilage contact: effect of compressive loading on tissue deformations and structural integrity of bovine articular cartilage

OBJECTIVE

This study aims to characterize the deformations in articular cartilage under compressive loading and link these to changes in the extracellular matrix constituents described by magnetic resonance imaging (MRI) relaxation times in an experimental model mimicking in vivo cartilage-on-cartilage contact.

DESIGN

Quantitative MRI images, T₁, T₂ and T_1ρ relaxation times, were acquired at 9.4T from bovine femoral osteochondral explants before and immediately after loading. Two-dimensional intra-tissue displacement and strain fields under cyclic compressive loading (350N) were measured using the displacement encoding with stimulated echoes (DENSE) method. Changes in relaxation times in response to loading were evaluated against the deformation fields.

RESULTS

Deformation fields showed consistent patterns among all specimens, with maximal strains at the articular surface that decrease with tissue depth. Axial and transverse strains were maximal around the center of the contact region, whereas shear strains were minimal around the contact center but increased towards contact edges. A decrease in T₂ and T_1ρ was observed immediately after loading whereas the opposite was observed for T₁. No correlations between cartilage deformation patterns and changes in relaxation times were observed.

CONCLUSIONS

Displacement encoding combined with relaxometry by MRI can noninvasively monitor the cartilage biomechanical and biochemical properties associated with loading. The deformation fields reveal complex patterns reflecting the depth-dependent mechanical properties, but intra-tissue deformation under compressive loading does not correlate with structural and compositional changes. The compacting effect of cyclic compression on the cartilage tissue was revealed by the change in relaxation time immediately after loading.

Functional assessment of strains around a full-thickness and critical sized articular cartilage defect under compressive loading using MRI

OBJECTIVE

The objective of this study was to evaluate the effect of full-thickness chondral defects on intratissue deformation patterns and matrix constituents in an experimental model mimicking in vivo cartilage-on-cartilage contact conditions.

DESIGN

Pairs of bovine osteochondral explants, in a unique cartilage-on-cartilage model system, were compressed uniaxially by 350 N during 2 s loading and 1.4 s unloading cycles (≈1700 repetitions). Tissue deformations under quasi-steady state load deformation response were measured with displacement encoded imaging with stimulated echoes (DENSE) in a 9.4 T magnetic resonance imaging (MRI) scanner. Pre- and post-loading, T₁, T₂ and T_1ρ relaxation time maps were measured. We analyzed differences in strain patterns and relaxation times between intact cartilage (n = 8) and cartilage in which a full-thickness and critical sized defect was created (n = 8).

RESULTS

Under compressive loading, strain magnitudes were elevated at the defect rim, with elevated tensile and compressive principal strains (Δϵ_max = 4.2%, P = 0.02; Δϵ_min = -4.3%, P = 0.02) and maximum shear strain at the defect rim (Δγ_max = 4.4%, P = 0.007). The opposing cartilage showed minimal increase in strain patterns at contact with the defect rim but decreased strains opposing the defect. After defect creation, T₁, T₂ and T_1ρ relaxation times were elevated at the defect rim only. Following loading, the overall relaxations times of the defect tissue and especially at the rim, increased compared to intact cartilage.

CONCLUSIONS

This study demonstrates that the local biomechanical changes occurring after defect creation may induce tissue damage by increasing shear strains and depletion of cartilage constituents at the defect rim under compressive loading.

Selective Enzymatic Digestion of Proteoglycans and Collagens Alters Cartilage T1rho and T2 Relaxation Times

Our objective was to determine the relationship of T1rho and T2 relaxation mapping to the biochemical and biomechanical properties of articular cartilage through selective digestion of proteoglycans and collagens. Femoral condyles were harvested from porcine knee joints and treated with either chondroitinase ABC (cABC) followed by collagenase, or collagenase followed by cABC. Magnetic resonance images were acquired and cartilage explants were harvested for biochemical, biomechanical, and histological analyses before and after each digestion. Targeted enzymatic digestion of proteoglycans with cABC resulted in elevated T1rho relaxation times and decreased sulfated glycosaminoglycan content without affecting T2 relaxation times. In contrast, extractable collagen and T2 relaxation times were increased by collagenase digestion; however, neither was altered by cABC digestion. Aggregate modulus decreased with digestion of both components. Overall, we found that targeted digestion of proteoglycans and collagens had varying effects on biochemical, biomechanical, and imaging properties. T2 relaxation times were altered with changes in extractable collagen, but not changes in proteoglycan. However, T1rho relaxation times were altered with proteoglycan loss, which may also coincide with collagen disruption. Since it is unclear which matrix components are disrupted first in osteoarthritis, both markers may be important for tracking disease progression.

Imaging of nuclear magnetic resonance spin-lattice relaxation activation energy in cartilage

Samples of human and bovine cartilage have been examined using magnetic resonance imaging to determine the proton nuclear magnetic resonance spin-lattice relaxation time, T₁, as a function of depth within through the cartilage tissue. T₁ was measured at five to seven temperatures between 8 and 38°C. From this, it is shown that the T₁ relaxation time is well described by Arrhenius-type behaviour and the activation energy of the relaxation process is quantified. The activation energy within the cartilage is approximately 11 ± 2 kJ mol^-1 with this notably being less than that for both pure water (16.6 ± 0.4 kJ mol^-1) and the phosphate-buffered solution in which the cartilage was immersed (14.7 ± 1.0 kJ mol^-1). It is shown that this activation energy increases as a function of depth in the cartilage. It is known that cartilage composition varies with depth, and hence, these results have been interpreted in terms of the structure within the cartilage tissue and the association of the water with the macromolecular constituents of the cartilage.

Magic angle effect plays a major role in both T1rho and T2 relaxation in articular cartilage

PURPOSE

To investigate the effect of sample orientation on T1rho and T2 values of articular cartilage in histologically confirmed normal and abnormal regions using a whole-body 3T scanner.

MATERIALS AND METHODS

Eight human cadaveric patellae were evaluated using a 2D CPMG sequence for T2 measurement as well as a 2D spin-locking prepared spiral sequence and a 3D magnetization-prepared angle-modulated partitioned-k-space spoiled gradient echo snapshots (3D MAPSS) sequence for T1rho measurement. Each sample was imaged at six angles from 0° to 100° relative to the B₀ field. T2 and T1rho values were measured for three regions (medial, apex and lateral) with three layers (10% superficial, 60% middle, 30% deep). Multiple histopathologically confirmed normal and abnormal regions were used to evaluate the angular dependence of T2 and T1rho relaxation in articular cartilage.

RESULTS

Our study demonstrated a strong magic angle effect for T1rho and T2 relaxation in articular cartilage, especially in the deeper layers of cartilage. On average, T2 values were increased by 231.8% (72.2% for superficial, 237.6% for middle, and 187.9% for deep layers) while T1rho values were increased by 92% (31.7% for superficial, 69% for middle, and 140% for deep layers) near the magic angle. Both normal and abnormal cartilage showed similar T1rho and T2 magic angle effect.

CONCLUSIONS

Changes in T1rho and T2 values due to the magic angle effect can be several times more than that caused by degeneration, and this may significantly complicate the clinical application of T1rho and T2 as an early surrogate marker for degeneration.

In Vivo Tibial Cartilage Strains in Regions of Cartilage-to-Cartilage Contact and Cartilage-to-Meniscus Contact in Response to Walking

BACKGROUND

There are currently limited human in vivo data characterizing the role of the meniscus in load distribution within the tibiofemoral joint. Purpose/Hypothesis: The purpose was to compare the strains experienced in regions of articular cartilage covered by the meniscus to regions of cartilage not covered by the meniscus. It was hypothesized that in response to walking, tibial cartilage covered by the meniscus would experience lower strains than uncovered tibial cartilage.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Magnetic resonance imaging (MRI) of the knees of 8 healthy volunteers was performed before and after walking on a treadmill. Using MRI-generated 3-dimensional models of the tibia, cartilage, and menisci, cartilage thickness was measured in 4 different regions based on meniscal coverage and compartment: covered medial, uncovered medial, covered lateral, and uncovered lateral. Strain was defined as the normalized change in cartilage thickness before and after activity.

RESULTS

Within each compartment, covered cartilage before activity was significantly thinner than uncovered cartilage before activity ( P < .001). After 20 minutes of walking, all 4 regions experienced significant cartilage thickness decreases ( P < .01). The covered medial region experienced significantly less strain than the uncovered medial region ( P = .04). No difference in strain was detected between the covered and uncovered regions in the lateral compartment ( P = .40).

CONCLUSION

In response to walking, cartilage that is covered by the meniscus experiences lower strains than uncovered cartilage in the medial compartment. These findings provide important baseline information on the relationship between in vivo tibial compressive strain responses and meniscal coverage, which is critical to understanding normal meniscal function.

Surgical Correction of Cam Deformity in Association with Femoroacetabular Impingement and Its Impact on the Degenerative Process within the Hip Joint

BACKGROUND

Cam morphology in association with femoroacetabular impingement (FAI) is a recognized cause of hip pain and cartilage damage and proposed as a leading cause of arthritis. The purpose of this study was to analyze the functional and biomechanical effects of the surgical correction of the cam deformity on the degenerative process associated with FAI.

METHODS

Ten male patients with a mean age of 34.3 years (range, 23.1 to 46.5 years) and a mean body mass index (and standard deviation) of 26.66 ± 4.79 kg/m underwent corrective surgery for cam deformity in association with FAI. Each patient underwent a computed tomography (CT) scan to assess acetabular bone mineral density (BMD), high-resolution T1ρ magnetic resonance imaging (MRI) of the hips to assess proteoglycan content, and squatting motion analysis as well as completed self-administered functional questionnaires (Hip disability and Osteoarthritis Outcome Score [HOOS]) both preoperatively and 2 years postoperatively.

RESULTS

At a mean follow-up of 24.5 months, improvements in functional scores and squat performance were seen. Regarding the zone of impingement in the anterosuperior quadrant of the acetabular rim, the mean change in BMD at the time of follow-up was -31.8 mg/cc (95% confidence interval [CI], -11 to -53 mg/cc) (p = 0.008), representing a 5% decrease in BMD. The anterosuperior quadrant also demonstrated a significant decrease in T1ρ values, reflecting a stabilization of the cartilage degeneration. Significant correlations were noted between changes in clinical functional scores and changes in T1ρ values (r = -0.86; p = 0.003) as well as between the BMD and maximum vertical force (r = 0.878; p = 0.021).

CONCLUSIONS

Surgical correction of a cam deformity in patients with symptomatic FAI not only improved clinical function but was also associated with decreases in T1ρ values and BMD. These findings are the first, to our knowledge, to show that alteration of the hip biomechanics through surgical intervention improves the overall health of the hip joint.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Quantitative analysis of T2 relaxation times of the patellofemoral joint cartilage 3 years after anterior cruciate ligament reconstruction

Objective

To evaluate patient-specific patellofemoral joint (PFJ) cartilage 3 years postoperatively using T2 mapping magnetic resonance imaging and the uninjured contralateral side as control.

Hypothesis

The cartilage of the PFJ in the anterior cruciate ligament (ACL) reconstructed knees would show increased T2 values compared to the uninjured contralateral knees at 3-year follow-up, and the femoral (trochlear) cartilage would be more susceptible than the patella in degeneration in ACL-reconstructed knees.

Methods

Ten patients with clinically successful ACL-reconstructed knees were prospectively enrolled 3 years postoperatively. Sagittal images of both knees were obtained using T2 mapping. Cartilage over the medial, central, and lateral regions of the trochlea and patella was divided into superficial and deep regions. Average T2 values of the cartilage at each region of interest of the ACL-reconstructed and uninjured contralateral knees were compared for each individual patient.

Results

Overall, the T2 values at the superficial layers of the medial and central trochlear cartilage of the ACL-reconstructed knees were significantly higher than those of the uninjured contralateral knees by 4.23 ± 9.09 milliseconds (8.9%; p = 0.043) and 5.94 ± 8.12 milliseconds (10.9%; p = 0.019), respectively. No significant difference was found in other cartilage areas of the trochlea and patella. In individual patient analysis, increased T2 values of ACL-reconstructed knees were found in all 10 patients in at least one superficial region and eight patients in at least one deep region of the trochlear cartilage, five patients in at least one superficial region, and eight patients in at least one deep region of the patellar cartilage.

Conclusion

Despite a clinically satisfactory ACL reconstruction (with negative anteroposterior drawer and pivot shift tests), all patients showed at least one region with increased T2 value of the PFJ cartilage 3 years after ACL reconstruction, especially at the medial compartment of the trochlear cartilage.

The Translational Potential of this Article

Little data has been reported on PFJ cartilage condition after ACL reconstruction. This study could help develop noninvasive diagnostic methods for detection of early PFJ cartilage degeneration after ACL reconstruction.

Degeneration of articular cartilage in osteonecrosis of the femoral head begins at the necrotic region after collapse: a preliminary study using T1 rho MRI

OBJECTIVE

The purpose of this study is to evaluate the role of collapse on the degeneration of articular cartilage in patients with osteonecrosis of the femoral head (ONFH).

MATERIALS AND METHODS

Sixteen hips in 12 patients (four men, eight women; mean age, 34.8 years) with a history of systemic corticosteroid treatment were studied using T1 rho magnetic resonance imaging (MRI). Six hips had collapsed ONFH, five had non-collapsed ONFH, and five had no osteonecrosis (controls). Using oblique coronal images, we divided the articular surface of necrotic femoral heads into a region just above the necrotic bone (necrotic zone) and another above the living bone (living zone). T1 rho value was evaluated for each zone.

RESULTS

The mean T1 rho value in the necrotic zone was significantly higher in the collapsed ONFH group (48.4 ± 2.7 ms) than in the non-collapsed ONFH group (41.0 ± 0.9 ms). In the collapsed ONFH group, the mean T1 rho value was significantly higher in the necrotic zone (48.4 ± 2.7 ms) than in the living zone (43.5 ± 2.5 ms). In the non-collapsed ONFH group, there was no significant difference between the mean T1 rho values of the necrotic and living zones. In the collapsed ONFH group, the mean T1 rho value of the necrotic zone and the interval from pain onset to the MRI examination were positively correlated.

CONCLUSIONS

The current T1 rho MRI study suggested that the degeneration of articular cartilage in ONFH begins at the necrotic region after collapse.

Properties of the cartilage layer from the cam-type hip impingement deformity

Femoro-acetabular impingement (FAI) is associated with significant acetabular cartilage damage and degenerative arthritis. To understand the contact stress and thus biomechanical mechanisms that may contribute to degeneration, the material behaviour of the cartilage layer is required. The objective of this study is to determine the fibril-reinforced poroelastic properties and composition of cartilage from cam deformities and to compare to those of normal cartilage. Patients undergoing surgical treatment of a symptomatic cam FAI deformity were recruited from the clinical practice of one of the authors. Osteochondral specimens were retrieved from the deformity during surgery using a trephine. Control specimens were retrieved from the anterior femoral head bearing surface during autopsy procedures. Indentation stress-relaxation tests were performed to determine the modulus (E_S), Poisson's ratio (ν) and permeability (k₀) of the poroelastic component, and the strain-independent (E₀) and -dependent (E_ε) moduli of the fibril-reinforcement using finite element analysis and optimization. Safranin-O staining was used to quantify proteoglycan content. E_S and ν were 71% and 37% lower, respectively, in Cam specimens compared to controls, and k₀ was approximately triple that of Control specimens (p<0.05). No significant differences were seen in the fibrillar components, E₀ and E_ε. Proteoglycan content was substantially depleted in Cam specimens, and was correlated with E_S, ν and k₀. This study showed that cartilage from the cam deformity exhibits severe degeneration in terms of the mechanical behaviour and composition changes, and is consistent with osteoarthritis. This further supports the hypothesis that FAI is a cause of hip osteoarthritis.

Relationship between T1rho magnetic resonance imaging, synovial fluid biomarkers, and the biochemical and biomechanical properties of cartilage

Non-invasive techniques for quantifying early biochemical and biomechanical changes in articular cartilage may provide a means of more precisely assessing osteoarthritis (OA) progression. The goals of this study were to determine the relationship between T1rho magnetic resonance (MR) imaging relaxation times and changes in cartilage composition, cartilage mechanical properties, and synovial fluid biomarker levels and to demonstrate the application of T1rho imaging to evaluate cartilage composition in human subjects in vivo. Femoral condyles and synovial fluid were harvested from healthy and OA porcine knee joints. Sagittal T1rho relaxation MR images of the condyles were acquired. OA regions of OA joints exhibited an increase in T1rho relaxation times as compared to non-OA regions. Furthermore in these regions, cartilage sGAG content and aggregate modulus decreased, while percent degraded collagen and water content increased. In OA joints, synovial fluid concentrations of sGAG decreased and C2C concentrations increased compared to healthy joints. T1rho relaxation times were negatively correlated with cartilage and synovial fluid sGAG concentrations and aggregate modulus and positively correlated with water content and permeability. Additionally, we demonstrated the application of these in vitro findings to the study of human subjects. Specifically, we demonstrated that walking results in decreased T1rho relaxation times, consistent with water exudation and an increase in proteoglycan concentration with in vivo loading. Together, these findings demonstrate that cartilage MR imaging and synovial fluid biomarkers provide powerful non-invasive tools for characterizing changes in the biochemical and biomechanical environments of the joint.

Feasibility study for evaluating early lumbar facet joint degeneration using axial T1 ρ, T2 , and T2* mapping in cartilage

PURPOSE

To assess the feasibility of axial T₂ , T2*, and T₁ ρ mapping of lumbar facet joint (LFJ) cartilage for evaluation of early degeneration.

MATERIALS AND METHODS

We examined a total of 176 LFJs from 21 volunteers using axial T₂ , T2*, and T₁ ρ mapping with a 3.0T magnetic resonance imaging (MRI) scanner. All LFJs were measured and grouped according to the presence of low back pain (LBP), the Weishaupt grading system, and the Pfirrmann grade of the adjacent intervertebral disk (IVD). T₂ , T2*, and T₁ ρ values were analyzed and compared among the different groups.

RESULTS

Low interobserver agreement was found in the Weishaupt grading of LFJs (κ = 0.161). The T₁ ρ values of LFJs were significantly different between adjacent two Pfirrmann grade of disks (grade I 50.15 ± 3.63 msec / grade II 53.27 ± 3.80 msec, P = 0.002; grade II 53.27 ± 3.80 msec / grade III 58.40 ± 4.17 msec, P < 0.01), and in different Weishaupt grades of LFJs (P = 0.000). T2* values were only found significantly different between Pfirrmann grade I and III of disks (P = 0.048). There was no significant difference in T₂ values of LFJs whatever in Pfirrmann (P = 0.556) or Weishaupt grades (P = 0.694). No significant difference was found in T₂ , T2*, and T₁ ρ values between volunteers with LBP and without LBP (P_T2  = 0.783, PT2*=0.311, P_T1 ρ = 0.259).

CONCLUSION

Axial T₁ ρ could be an effective and sensitive method to assess for early degenerative changes in LFJ cartilage.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:468-475.

Use of T1ρMR imaging in Sjögren's syndrome with normal appearing parotid glands: Initial findings

PURPOSE

To explore the feasibility of parotid spin-lattice relaxation time in the rotating frame (T1ρ) MR imaging in the diagnosis of Sjögren's syndrome (SS) without morphological changes of the parotid glands.

MATERIALS AND METHODS

The study enrolled 32 consecutive SS patients without morphological changes of parotid glands and 32 age- and gender-matched healthy volunteers who underwent parotid 3.0 Tesla MR imaging, including T1ρ sequences. Follow-up imaging was performed at 3 months. T1 signal intensities and T1ρ values of bilateral parotid glands were compared using paired samples t-test. Parotid T1 signal intensities and T1ρ values were compared using two independent samples t-test. Diagnostic performance of the parotid T1ρ values was evaluated by receiver operating characteristic analysis. The intraclass correlation coefficient (ICC) was calculated to evaluate the reproducibility of parotid T1ρ measurements.

RESULTS

There were no significant differences of T1 signal intensities and T1ρ values between bilateral parotid glands in SS patients and healthy volunteers (P = 0.170, 0.886 and 0.942, 0.229). The parotid T1ρ values of SS patients (96.47 ± 15.38 ms) were significantly higher than those of healthy volunteers (84.25 ± 6.11 ms) (P < 0.001), while there were no significant differences of T1 signal intensities between SS patients and healthy volunteers (P = 0.655). With a cutoff value of 88.02 ms, the sensitivity and specificity of the parotid T1ρ value was 75.0% and 100.0% in the diagnosis of SS. The reproducibility of parotid T1ρ measurement was excellent (ICC: 0.934-0.995).

CONCLUSION

Parotid T1ρ MR imaging held a potential role in diagnosing SS without morphological changes of parotid glands.

LEVEL OF EVIDENCE

2 J. Magn. Reson. Imaging 2017;45:1005-1012.

Multi-parametric MRI characterization of enzymatically degraded articular cartilage

Several laboratory and rotating frame quantitative MRI parameters were evaluated and compared for detection of changes in articular cartilage following selective enzymatic digestion. Bovine osteochondral specimens were subjected to 44 h incubation in control medium or in collagenase or chondroitinase ABC to induce superficial collagen or proteoglycan (glycosaminoglycan) alterations. The samples were scanned at 9.4 T for T1 , T1 Gd (dGEMRIC), T2 , adiabatic T1 ρ , adiabatic T2 ρ , continuous-wave T1 ρ , TRAFF2 , and T1 sat relaxation times and for magnetization transfer ratio (MTR). For reference, glycosaminoglycan content, collagen fibril orientation and biomechanical properties were determined. Changes primarily in the superficial cartilage were noted after enzymatic degradation. Most of the studied parameters were sensitive to the destruction of collagen network, whereas glycosaminoglycan depletion was detected only by native T1 and T1 Gd relaxation time constants throughout the tissue and by MTR superficially. T1 , adiabatic T1 ρ , adiabatic T2 ρ , continuous-wave T1 ρ , and T1 sat correlated significantly with the biomechanical properties while T1 Gd correlated with glycosaminoglycan staining. The findings indicated that most of the studied MRI parameters were sensitive to both glycosaminoglycan content and collagen network integrity, with changes due to enzymatic treatment detected primarily in the superficial tissue. Strong correlation of T1 , adiabatic T1ρ , adiabatic T2 ρ , continuous-wave T1 ρ , and T1 sat with the altered biomechanical properties, reflects that these parameters were sensitive to critical functional properties of cartilage. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1111-1120, 2016.

MR morphology of triangular fibrocartilage complex: correlation with quantitative MR and biomechanical properties

OBJECTIVE

To evaluate pathology of the triangular fibrocartilage complex (TFCC) using high-resolution morphologic magnetic resonance (MR) imaging, and compare with quantitative MR and biomechanical properties.

MATERIALS AND METHODS

Five cadaveric wrists (22-70 years) were imaged at 3 T using morphologic (proton density weighted spin echo, PD FS, and 3D spoiled gradient echo, 3D SPGR) and quantitative MR sequences to determine T2 and T1rho properties. In eight geographic regions, morphology of TFC disc and laminae were evaluated for pathology and quantitative MR values. Samples were disarticulated and biomechanical indentation testing was performed on the distal surface of the TFC disc.

RESULTS

On morphologic PD SE images, TFC disc pathology included degeneration and tears, while that of the laminae included degeneration, degeneration with superimposed tear, mucinous transformation, and globular calcification. Punctate calcifications were highly visible on 3D SPGR images and found only in pathologic regions. Disc pathology occurred more frequently in proximal regions of the disc than distal regions. Quantitative MR values were lowest in normal samples, and generally higher in pathologic regions. Biomechanical testing demonstrated an inverse relationship, with indentation modulus being high in normal regions with low MR values. The laminae studied were mostly pathologic, and additional normal samples are needed to discern quantitative changes.

CONCLUSION

These results show technical feasibility of morphologic MR, quantitative MR, and biomechanical techniques to characterize pathology of the TFCC. Quantitative MRI may be a suitable surrogate marker of soft tissue mechanical properties, and a useful adjunct to conventional morphologic MR techniques.

Comparison of multiple quantitative MRI parameters for characterization of the goat cartilage in an ongoing osteoarthritis: dGEMRIC, T1ρ and sodium

RATIONALE AND OBJECTIVES

Osteoarthritis (OA) is a degenerative joint disease leading to cartilage deterioration by loss of matrix, fibrillation, formation of fissures, and ultimately complete loss of the cartilage surface. Here, three magnetic resonance imaging (MRI) techniques, dGEMRIC (delayed Gadolinium enhanced MRI of cartilage; dG1=T1,post; dG2=1/T1,post-1/T1,pre), T1ρ,and sodium MRI, are compared in a preclinical in vivo study to evaluate the differences in their potential for cartilage characterization and to establish an examination protocol for a following clinical study.

MATERIALS AND METHODS

OA was induced in 12 caprine knees (6 control, 6 therapy). Adipose derived stem cells were injected afterwards as a treatment. The animals were examined healthy, 3 and 16 weeks postoperatively with all three MRI methods. Using statistical analysis, the OA development and the degree of correlation between the different MRI methods were determined.

RESULTS

A strong correlation was observed between the dGEMRIC indices dG1 and dG2 (r=-0.87) which differ only in considering or not considering the T1 baseline. Moderate correlations were found between T1ρ and dG1 (r=0.55), T1ρ and dG2 (r=0.47) and at last, sodium and dG1 (r=0.45). The correlations found in this study match to the biomarkers which the methods are sensitive to.

CONCLUSION

Even though the goat cartilage is significantly thinner than the human cartilage and even more in a degenerated cartilage, all three methods were able to characterize the cartilage over the whole period of time during an ongoing OA. Due to measurement and post processing optimizations, as well as the correlations detected in this work, the overall measurement time in future goat studies can be minimized. Moreover, an examination protocol for characterizing the cartilage in a clinical study was established.

T1ρ magnetic resonance: basic physics principles and applications in knee and intervertebral disc imaging

T1ρ relaxation time provides a new contrast mechanism that differs from T1- and T2-weighted contrast, and is useful to study low-frequency motional processes and chemical exchange in biological tissues. T1ρ imaging can be performed in the forms of T1ρ-weighted image, T1ρ mapping and T1ρ dispersion. T1ρ imaging, particularly at low spin-lock frequency, is sensitive to B0 and B1 inhomogeneity. Various composite spin-lock pulses have been proposed to alleviate the influence of field inhomogeneity so as to reduce the banding-like spin-lock artifacts. T1ρ imaging could be specific absorption rate (SAR) intensive and time consuming. Efforts to address these issues and speed-up data acquisition are being explored to facilitate wider clinical applications. This paper reviews the T1ρ imaging's basic physic principles, as well as its application for cartilage imaging and intervertebral disc imaging. Compared to more established T2 relaxation time, it has been shown that T1ρ provides more sensitive detection of proteoglycan (PG) loss at early stages of cartilage degeneration. T1ρ has also been shown to provide more sensitive evaluation of annulus fibrosis (AF) degeneration of the discs.

Assessment of liver fibrosis in rats by MRI with apparent diffusion coefficient and T1 relaxation time in the rotating frame

PURPOSE

To explore the value of T1 relaxation times in the rotating frame (T1 ρ or T1 rho) for evaluating liver fibrosis stage, compared to apparent diffusion coefficients (ADCs).

MATERIALS AND METHODS

Liver fibrosis in model rats (n = 50) was produced by carbon tetrachloride (CCl4 ) injection. Five rats died during the experiment. Surviving model rats (n = 45) and controls (n = 15) were subjected to 3.0T MRI and the ADCs (b-values: 0, 800 s/mm(2) ) and T1 ρ values were determined. Liver fibrosis stage (F0-F4) was defined based on METAVIR scoring. Nonparametric statistical methods and receiver operating characteristic (ROC) curve analyses were employed to determine diagnostic accuracy.

RESULTS

Mean ADC and T1 ρ associated negatively (r = -0.732 P < 0.001) and positively (r = 0.863 P < 0.001), respectively, with severity of fibrosis stage. Analysis of ROC curves for fibrosis staging showed that the area under the curve (AUC) for T1 ρ (stage F0 vs. F1-F4 = 0.976, stage F0-F1 vs. F2-F4 = 0.920, stage F0-F2 vs. F3-F4 = 0.938, and stage F0-F3 vs. F4 = 0.931) was larger than that for ADCs (0.917, 0.924, 0.842, and 0.781, respectively).

CONCLUSION

ADC and T1 ρ values correlate with liver fibrosis stage. The performance of the T1 ρ parameter was superior to that of the ADC parameter in the differentiation of liver fibrosis stages in a CCl4 rat model.

Noninvasive assessment of osteoarthritis severity in human explants by multicontrast MRI

PURPOSE

Medical imaging has the potential to noninvasively diagnose early disease onset and monitor the success of repair therapies. Unfortunately, few reliable imaging biomarkers exist to detect cartilage diseases before advanced degeneration in the tissue.

METHOD

In this study, we quantified the ability to detect osteoarthritis (OA) severity in human cartilage explants using a multicontrast magnetic resonance imaging (MRI) approach, inclusive of novel displacements under applied loading by MRI, relaxivity measures, and standard MRI.

RESULTS

Displacements under applied loading by MRI measures, which characterized the spatial micromechanical environment by 2D finite and Von Mises strains, were strong predictors of histologically assessed OA severity, both before and after controlling for factors, e.g., patient, joint region, and morphology. Relaxivity measures, sensitive to local macromolecular weight and composition, including T1ρ, but not T1 or T2, were predictors of OA severity. A combined multicontrast approach that exploited spatial variations in tissue biomechanics and extracellular matrix structure yielded the strongest relationships to OA severity.

CONCLUSION

Our results indicate that combining multiple MRI-based biomarkers has high potential for the noninvasive measurement of OA severity and the evaluation of potential therapeutic agents used in the treatment of early OA in animal and human trials.

Cartilage T1ρ and T2 Relaxation Times in Patients With Mild-to-Moderate Radiographic Hip Osteoarthritis

OBJECTIVE

To analyze region-specific T1ρ and T2 relaxation times of the hip joint cartilage in relation to presence or absence of radiographic hip osteoarthritis (OA) and presence or absence of magnetic resonance imaging (MRI)-detected cartilage defects.

METHODS

Weight-bearing radiographs and 3T MRI studies of the hip were obtained from 84 volunteers. Based on Kellgren/Lawrence (K/L) scoring of the radiographs, 54 subjects were classified as healthy controls (K/L grade ≤1) and 30 were classified as having mild or moderate radiographic hip OA (K/L grades 2 or 3, respectively). Two-dimensional fat-suppressed fast spin-echo MRI sequences were used for semiquantitative clinical scoring of cartilage defects, and a T1ρ/T2 sequence was used to quantitatively assess the cartilage matrix. The femoral and acetabular cartilage was then segmented into 8 regions and the mean T1ρ/T2 values were calculated. Differences in T1ρ and T2 relaxation times were compared between subjects with and those without radiographic hip OA, and those with and those without femoral or acetabular cartilage defects.

RESULTS

Higher T1ρ and T2 relaxation times in the anterior superior and central regions of the acetabular cartilage were seen in individuals with radiographic hip OA and those with acetabular cartilage defects compared to their respective controls (P < 0.05). In the femoral cartilage, the differences in T1ρ and T2 were not significant for any of the comparisons. Significant differences in the T1ρ and T2 values (each P < 0.05) were found in more subregions of the cartilage and across the whole cartilage when subjects were stratified based on the presence of MRI-detected cartilage defects than when they were stratified based on the presence of radiographic hip OA.

CONCLUSION

T1ρ and T2 relaxation parameters are sensitive to the presence of cartilage degeneration. Both parameters may therefore support MRI evidence of cartilage defects of the hip.

Is the contralateral hip at risk in patients with unilateral symptomatic cam femoroacetabular impingement? A quantitative T1ρ MRI study

OBJECTIVES

To assess the profile of weight-bearing cartilage of hips with a cam deformity using T1ρ magnetic resonance imaging (MRI) and evaluate for a side-to-side difference in the T1ρ profile of patients with bilateral cam morphology but only unilateral hip pain.

METHODS

19 patients with bilateral cam morphology undergoing osteochondroplasty for unilateral hip pain were prospectively recruited. Anterior and anterosuperior alpha angles were measured using computer tomography. All patients underwent bilateral 1.5T T1ρ MRI. The cartilage bilayer of the hip joint was evaluated and the mean T1ρ relaxation time calculated for each quadrant of the weight-bearing surface.

RESULTS

Mean T1ρ relaxation times were not significantly different when each quadrant was compared to the rest of the weight-bearing surface of the symptomatic (P = 0.068) and asymptomatic hips (P = 0.102). There was also no significant side-to-side difference between the same quadrants of symptomatic and asymptomatic hips. No correlation was detected between alpha angle and the mean T1ρ relaxation time in each quadrant. There was no significant difference in mean alpha angles between the symptomatic and asymptomatic sides at the anterior (54.2 vs 56.0°; P = 0.382) and anterosuperior positions (65.1 vs 65.2°; P = 0.971).

CONCLUSION

We conclude that previously observed regional variation in T1ρ values of normal hips is altered in hips with cam morphology. No difference in T1ρ values between symptomatic and asymptomatic cam hips was demonstrated. Therefore, regardless of the presence of hip pain, a cam deformity may predispose to hip joint cartilage degradation and increase the risk of hip osteoarthritis.

Advanced Imaging in Femoroacetabular Impingement: Current State and Future Prospects

Symptomatic femoroacetabular impingement (FAI) is now a known precursor of early osteoarthritis (OA) of the hip. In terms of clinical intervention, the decision between joint preservation and joint replacement hinges on the severity of articular cartilage degeneration. The exact threshold during the course of disease progression when the cartilage damage is irreparable remains elusive. The intention behind radiographic imaging is to accurately identify the morphology of osseous structural abnormalities and to accurately characterize the chondrolabral damage as much as possible. However, both plain radiographs and computed tomography (CT) are insensitive for articular cartilage anatomy and pathology. Advanced magnetic resonance imaging (MRI) techniques include magnetic resonance arthrography and biochemically sensitive techniques of delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), T1rho (T1ρ), T2/T2* mapping, and several others. The diagnostic performance of these techniques to evaluate cartilage degeneration could improve the ability to predict an individual patient-specific outcome with non-surgical and surgical care. This review discusses the facts and current applications of biochemical MRI for hip joint cartilage assessment covering the roles of dGEMRIC, T2/T2*, and T1ρ mapping. The basics of each technique and their specific role in FAI assessment are outlined. Current limitations and potential pitfalls as well as future directions of biochemical imaging are also outlined.

OARSI Clinical Trials Recommendations: Hip imaging in clinical trials in osteoarthritis

Imaging of hip in osteoarthritis (OA) has seen considerable progress in the past decade, with the introduction of new techniques that may be more sensitive to structural disease changes. The purpose of this expert opinion, consensus driven recommendation is to provide detail on how to apply hip imaging in disease modifying clinical trials. It includes information on acquisition methods/techniques (including guidance on positioning for radiography, sequence/protocol recommendations/hardware for magnetic resonance imaging (MRI)); commonly encountered problems (including positioning, hardware and coil failures, artifacts associated with various MRI sequences); quality assurance/control procedures; measurement methods; measurement performance (reliability, responsiveness, and validity); recommendations for trials; and research recommendations.

Is the T1ρ MRI profile of hyaline cartilage in the normal hip uniform?

BACKGROUND

T1ρ MRI is an imaging technique sensitive to proteoglycan (PG) content of hyaline cartilage. However, normative T1ρ values have not been established for the weightbearing cartilage of the hip, and it is not known whether it is uniform or whether there is topographic variation. Knowledge of the T1ρ profile of hyaline cartilage in the normal hip is important for establishing a baseline against which comparisons can be made to experimental and clinical arthritic subjects.

QUESTIONS/PURPOSES

In this diagnostic study, we determined (1) the T1ρ MRI values of hyaline cartilage of the normal hip; and (2) whether the T1ρ MRI profile of the normal hip hyaline cartilage is uniform.

METHODS

Fourteen asymptomatic volunteers (11 men, three women; mean age, 35 years) prospectively underwent 1.5-T T1ρ MRI of a single hip. The weightbearing hyaline cartilage bilayer of the acetabulum and femoral head was evaluated on sagittal images and segmented into four zones: (1) anterior; (2) anterosuperior; (3) posterosuperior; and (4) and posterior. For the full region of interest and within each zone and each sagittal slice, we calculated the mean T1ρ relaxation value, a parameter that indirectly quantifies PG content, where T1ρ is inversely related to PG concentration.

RESULTS

There was variation in the T1ρ relaxation values depending on zone (anterior to posterior) and slice (medial to lateral). When combining the most anterior quadrants (Zones 1 and 2), the T1ρ relaxation values were lower than those in the combined posterior quadrants (Zones 3 and 4) (30.4 msec versus 32.2 msec, respectively; p = 0.002), reflecting higher PG concentration. There was a difference between the T1ρ relaxation values of the sagittal slices (p = 0.038), most pronounced anteriorly in Zone 1 (26.6 msec, p = 0.001). With a selective combination of zones and slices, there were lower mean T1ρ values in the anterolateral-most region compared with the remainder of the weightbearing portion of the hip (28.6 msec versus 32.2 msec, respectively; p = 0.001).

CONCLUSIONS

The T1ρ profile of normal hyaline cartilage of the hip is not uniform with the topographic differences identified suggesting regional variations in PG concentration. This study, through determination of lower T1ρ relaxation values, suggests inherently greater PG concentrations in the more anterolateral region of the normal hip hyaline cartilage. Furthermore, it demonstrates that T1ρ MRI has the ability to detect even subtle, microscopic local differences in hyaline cartilage composition. This technique has the potential to facilitate basic science and clinical research by serving as a noninvasive surrogate or biomarker of cartilage health and thus may be added to the growing repertoire of advanced, biochemical MRI techniques for evaluating hyaline cartilage.

T1rho MRI and CSF biomarkers in diagnosis of Alzheimer's disease

In the current study, we have evaluated the performance of magnetic resonance (MR) T1rho (T_1ρ) imaging and CSF biomarkers (T-tau, P-tau and Aβ-42) in characterization of Alzheimer's disease (AD) patients from mild cognitive impairment (MCI) and control subjects. With informed consent, AD (n = 27), MCI (n = 17) and control (n = 17) subjects underwent a standardized clinical assessment and brain MRI on a 1.5-T clinical-scanner. T_1ρ images were obtained at four different spin-lock pulse duration (10, 20, 30 and 40 ms). T_1ρ maps were generated by pixel-wise fitting of signal intensity as a function of the spin-lock pulse duration. T_1ρ values from gray matter (GM) and white matter (WM) of medial temporal lobe were calculated. The binary logistic regression using T_1ρ and CSF biomarkers as variables was performed to classify each group. T_1ρ was able to predict 77.3% controls and 40.0% MCI while CSF biomarkers predicted 81.8% controls and 46.7% MCI. T_1ρ and CSF biomarkers in combination predicted 86.4% controls and 66.7% MCI. When comparing controls with AD, T_1ρ predicted 68.2% controls and 73.9% AD, while CSF biomarkers predicted 77.3% controls and 78.3% for AD. Combination of T_1ρ and CSF biomarkers improved the prediction rate to 81.8% for controls and 82.6% for AD. Similarly, on comparing MCI with AD, T_1ρ predicted 35.3% MCI and 81.9% AD, whereas CSF biomarkers predicted 53.3% MCI and 83.0% AD. Collectively CSF biomarkers and T_1ρ were able to predict 59.3% MCI and 84.6% AD. On receiver operating characteristic analysis T_1ρ showed higher sensitivity while CSF biomarkers showed greater specificity in delineating MCI and AD from controls. No significant correlation between T_1ρ and CSF biomarkers, between T_1ρ and age, and between CSF biomarkers and age was observed. The combined use of T_1ρ and CSF biomarkers have promise to improve the early and specific diagnosis of AD. Furthermore, disease progression form MCI to AD might be easily tracked using these two parameters in combination.

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Increased T1rho was observed in MCI and AD compared to controls.

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Increased T-tau and P-tau and decreased Aβ1-42 were observed in MCI and AD.

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Combined biomarkers have promise to improve early and specific diagnosis of AD.

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MCI to AD progression might be tracked using these two biomarkers in combination.

Towards quantification of pulsed spinlock and CEST at clinical MR scanners: an analytical interleaved saturation-relaxation (ISAR) approach

Off-resonant spinlock (SL) enables an NMR imaging technique that can detect dilute metabolites similar to chemical exchange saturation transfer. However, in clinical MR scanners, RF pulse widths are restricted due to recommended specific absorption rate limits. Therefore, trains of short RF pulses that provide effective saturation during the required irradiation period are commonly employed. Quantitative evaluation of spectra obtained by pulsed saturation schemes is harder to achieve, since the theory of continuous wave saturation cannot be applied directly. In this paper we demonstrate the general feasibility of quantifying proton exchange rates from data obtained in pulsed SL experiments on a clinical 3 T MR scanner. We also propose a theoretical treatment of pulsed SL in the presence of chemical exchange using an interleaved saturation-relaxation approach. We show that modeling magnetization transfer during the pauses between the RF pulses is crucial, especially in the case of exchange rates that are small with respect to the delay times. The dynamics is still governed by a monoexponential decay towards steady state, for which we give the effective rate constant. The derived analytical model agrees well with the full numerical simulation of the Bloch-McConnell equations for a broad range of values of the system parameters.

Quantitative magnetic resonance imaging of the articular cartilage of the knee joint

Osteoarthritis is characterized by a decrease in the proteoglycan content and disruption of the highly organized collagen fiber network of articular cartilage. Various quantitative magnetic resonance imaging techniques have been developed for noninvasive assessment of the proteoglycan and collagen components of cartilage. These techniques have been extensively used in clinical practice to detect early cartilage degeneration and in osteoarthritis research studies to monitor disease-related and treatment-related changes in cartilage over time. This article reviews the role of quantitative magnetic resonance imaging in evaluating the composition and ultrastructure of the articular cartilage of the knee joint.

Imaging following acute knee trauma

Joint injury has been recognized as a potent risk factor for the onset of osteoarthritis. The vast majority of studies using imaging technology for longitudinal assessment of patients following joint injury have focused on the injured knee joint, specifically in patients with anterior cruciate ligament injury and meniscus tears where a high risk for rapid onset of post-traumatic osteoarthritis is well known. Although there are many imaging modalities under constant development, magnetic resonance (MR) imaging is the most important instrument for longitudinal monitoring after joint injury. MR imaging is sensitive for detecting early cartilage degeneration and can evaluate other joint structures including the menisci, bone marrow, tendons, and ligaments which can be sources of pain following acute injury. In this review, focusing on imaging following acute knee trauma, several studies were identified with promising short-term results of osseous and soft tissue changes after joint injury. However, studies connecting these promising short-term results to the development of osteoarthritis were limited which is likely due to the long follow-up periods needed to document the radiographic and clinical onset of the disease. Thus, it is recommended that additional high quality longitudinal studies with extended follow-up periods be performed to further investigate the long-term consequences of the early osseous and soft tissue changes identified on MR imaging after acute knee trauma.