Search

Purpose: The anisotropy of R2 and R1ρ relaxation rates in articular cartilage contains information about the collagenous structure of the tissue. Here we determine and study the anisotropic and isotropic components of T2 and T1ρ relaxation parameters in articular cartilage with a clinical 3T MRI device. Furthermore, a visual representation of the topographical variation in anisotropy is given via anisotropy mapping. Methods: Eight bovine stifle joints were imaged at 22 orientations with respect to the main magnetic field using T2, continuous‐wave (CW) T1ρ, and adiabatic T1ρ mapping sequences. Relaxation rates were separated into isotropic and anisotropic relaxation components using a previously established relaxation anisotropy model. Pixel‐wise anisotropy values were determined from the relaxation‐time maps using Michelson contrast. Results: The relaxation rates obtained from the samples displayed notable variation depending on the sample orientation, magnetization preparation, and cartilage layer. R2 demonstrated significant anisotropy, whereas CW‐R1ρ (300 Hz) and CW‐R1ρ (500 Hz) displayed a low degree of anisotropy. Adiabatic R1ρ was largely isotropic. In the deep cartilage regions, relaxation rates were generally faster and more anisotropic than in the cartilage closer to the tissue surface. The isotropic relaxation rate components were found to have similar values regardless of measurement sequence. Conclusions: The fitted relaxation model for T2 and T1ρ demonstrated varying amounts anisotropy, depending on magnetization preparation, and studied the articular cartilage layer. Anisotropy mapping of full joints showed varying amounts of anisotropy depending on the quantitative MRI parameter and topographical location, and in the case of T2, showed systematic changes in anisotropy across cartilage depth. [ABSTRACT FROM AUTHOR]

The aim of this study is to assess whether articular cartilage changes in an equine model of post‐traumatic osteoarthritis (PTOA), induced by surgical creation of standard (blunt) grooves, and very subtle sharp grooves, could be detected with ex vivo T1 relaxation time mapping utilizing three‐dimensional (3D) readout sequence with zero echo time. Grooves were made on the articular surfaces of the middle carpal and radiocarpal joints of nine mature Shetland ponies and osteochondral samples were harvested at 39 weeks after being euthanized under respective ethical permissions. T1 relaxation times of the samples (n = 8 + 8 for experimental and n = 12 for contralateral controls) were measured with a variable flip angle 3D multiband‐sweep imaging with Fourier transform sequence. Equilibrium and instantaneous Young's moduli and proteoglycan (PG) content from OD of Safranin‐O‐stained histological sections were measured and utilized as reference parameters for the T1 relaxation times. T1 relaxation time was significantly (p < 0.05) increased in both groove areas, particularly in the blunt grooves, compared with control samples, with the largest changes observed in the superficial half of the cartilage. T1 relaxation times correlated weakly (Rs ≈ 0.33) with equilibrium modulus and PG content (Rs ≈ 0.21). T1 relaxation time in the superficial articular cartilage is sensitive to changes induced by the blunt grooves but not to the much subtler sharp grooves, at the 39‐week timepoint post‐injury. These findings support that T1 relaxation time has potential in detection of mild PTOA, albeit the most subtle changes could not be detected. [ABSTRACT FROM AUTHOR]

Objective. To provide orientation-independent MR parameters potentially sensitive to articular cartilage degeneration by measuring isotropic and anisotropic components of T 2 relaxation, as well as 3D fiber orientation angle and anisotropy via multi-orientation MR scans. Approach. Seven bovine osteochondral plugs were scanned with a high angular resolution of thirty-seven orientations spanning 180° at 9.4 T. The obtained data was fitted to the magic angle model of anisotropic T 2 relaxation to produce pixel-wise maps of the parameters of interest. Quantitative Polarized Light Microscopy (qPLM) was used as a reference method for the anisotropy and fiber orientation. Main results. The number of scanned orientations was found to be sufficient for estimating both fiber orientation and anisotropy maps. The relaxation anisotropy maps demonstrated a high correspondence with qPLM reference measurements of the collagen anisotropy of the samples. The scans also enabled calculating orientation-independent T 2 maps. Little spatial variation was observed in the isotropic component of T 2 while the anisotropic component was much faster in the deep radial zone of cartilage. The estimated fiber orientation spanned the expected 0°–90° in samples that had a sufficiently thick superficial layer. The orientation-independent magnetic resonance imaging (MRI) measures can potentially reflect the true properties of articular cartilage more precisely and robustly. Significance. The methods presented in this study will likely improve the specificity of cartilage qMRI by allowing the assessment of the physical properties such as orientation and anisotropy of collagen fibers in articular cartilage. [ABSTRACT FROM AUTHOR]

Background: Machine learning models trained with multiparametric quantitative MRIs (qMRIs) have the potential to provide valuable information about the structural composition of articular cartilage. Purpose: To study the performance and feasibility of machine learning models combined with qMRIs for noninvasive assessment of collagen fiber orientation and proteoglycan content. Study Type: Retrospective, animal model. Animal Model: An open‐source single slice MRI dataset obtained from 20 samples of 10 Shetland ponies (seven with surgically induced cartilage lesions followed by treatment and three healthy controls) yielded to 1600 data points, including 10% for test and 90% for train validation. Field Strength/Sequence: A 9.4 T MRI scanner/qMRI sequences: T1, T2, adiabatic T1ρ and T2ρ, continuous‐wave T1ρ and relaxation along a fictitious field (TRAFF) maps. Assessment: Five machine learning regression models were developed: random forest (RF), support vector regression (SVR), gradient boosting (GB), multilayer perceptron (MLP), and Gaussian process regression (GPR). A nested cross‐validation was used for performance evaluation. For reference, proteoglycan content and collagen fiber orientation were determined by quantitative histology from digital densitometry (DD) and polarized light microscopy (PLM), respectively. Statistical Tests: Normality was tested using Shapiro–Wilk test, and association between predicted and measured values was evaluated using Spearman's Rho test. A P‐value of 0.05 was considered as the limit of statistical significance. Results: Four out of the five models (RF, GB, MLP, and GPR) yielded high accuracy (R2 = 0.68–0.75 for PLM and 0.62–0.66 for DD), and strong significant correlations between the reference measurements and predicted cartilage matrix properties (Spearman's Rho = 0.72–0.88 for PLM and 0.61–0.83 for DD). GPR algorithm had the highest accuracy (R2 = 0.75 and 0.66) and lowest prediction‐error (root mean squared [RMSE] = 1.34 and 2.55) for PLM and DD, respectively. Data Conclusion: Multiparametric qMRIs in combination with regression models can determine cartilage compositional and structural features, with higher accuracy for collagen fiber orientation than proteoglycan content. Evidence Level: 2 Technical Efficacy: Stage 2 [ABSTRACT FROM AUTHOR]

Abnormal loading of the knee due to injuries or obesity is thought to contribute to the development of osteoarthritis (OA). Small animal models have been used for studying OA progression mechanisms. However, numerical models to study cartilage responses under dynamic loading in preclinical animal models have not been developed. Here we present a musculoskeletal finite element model of a rat knee joint to evaluate cartilage biomechanical responses during a gait cycle. The rat knee joint geometries were obtained from a 3-D MRI dataset and the boundary conditions regarding loading in the joint were extracted from a musculoskeletal model of the rat hindlimb. The fibril-reinforced poroelastic (FRPE) properties of the rat cartilage were derived from data of mechanical indentation tests. Our numerical results showed the relevance of simulating anatomical and locomotion characteristics in the rat knee joint for estimating tissue responses such as contact pressures, stresses, strains, and fluid pressures. We found that the contact pressure and maximum principal strain were virtually constant in the medial compartment whereas they showed the highest values at the beginning of the gait cycle in the lateral compartment. Furthermore, we found that the maximum principal stress increased during the stance phase of gait, with the greatest values at midstance. We anticipate that our approach serves as a first step towards investigating the effects of gait abnormalities on the adaptation and degeneration of rat knee joint tissues and could be used to evaluate biomechanically-driven mechanisms of the progression of OA as a consequence of joint injury or obesity. Author summary: Osteoarthritis is a disease of the musculoskeletal system which is characterized by the degradation of articular cartilage. Changes in the knee loading after injuries or obesity contribute to the development of cartilage degeneration. Since injured cartilage cannot be reversed back to intact conditions, small animal models have been widely used for investigating osteoarthritis progression mechanisms. Moreover, experimental studies have been complemented with numerical models to overcome inherent limitations such as cost, difficulties to obtain accurate measures and replicate degenerative situations in the knee joint. However, computational models to study articular cartilage responses under dynamic loading in small animal models have not been developed. Thus, here we present a musculoskeletal finite element model (MSFE) of a rat knee joint to evaluate cartilage biomechanical responses during gait. Our computational model considers both the anatomical and locomotion characteristics of the rat knee joint for estimating mechanical responses in the articular cartilage. We suggest that our approach can be used to investigate tissue adaptations based on the mechanobiological responses of the cartilage to prevent the progression of osteoarthritis. [ABSTRACT FROM AUTHOR]

To prevent the progression of posttraumatic osteoarthritis, assessment of cartilage composition is critical for effective treatment planning. Posttraumatic changes include proteoglycan (PG) loss and elevated water content. Quantitative dual‐energy computed tomography (QDECT) provides a means to diagnose these changes. Here, we determine the potential of QDECT to evaluate tissue quality surrounding cartilage lesions in an equine model, hypothesizing that QDECT allows detection of posttraumatic degeneration by providing quantitative information on PG and water contents based on the partitions of cationic and nonionic agents in a contrast mixture. Posttraumatic osteoarthritic samples were obtained from a cartilage repair study in which full‐thickness chondral defects were created surgically in both stifles of seven Shetland ponies. Control samples were collected from three nonoperated ponies. The experimental (n = 14) and control samples (n = 6) were immersed in the contrast agent mixture and the distributions of the agents were determined at various diffusion time points. As a reference, equilibrium moduli, dynamic moduli, and PG content were measured. Significant differences (p < 0.05) in partitions between the experimental and control samples were demonstrated with cationic contrast agent at 30 min, 60 min, and 20 h, and with non‐ionic agent at 60 and 120 min. Significant Spearman's rank correlations were obtained at 20 and 24 h (ρ = 0.482–0.693) between the partition of cationic contrast agent, cartilage biomechanical properties, and PG content. QDECT enables evaluation of posttraumatic changes surrounding a lesion and quantification of PG content, thus advancing the diagnostics of the extent and severity of cartilage injuries. [ABSTRACT FROM AUTHOR]

This article is a review of various quantitative MRI methods for assessing cartilage. The authors address a concern regarding the interpretation of T1ρ mapping as an indirect measure of glycosaminoglycan (GAG) content in cartilage. While T1ρ has been correlated with GAG loss in some studies, it is important to recognize that variations in T1ρ values can also reflect changes in other tissue components, such as collagen structure. The authors suggest that attributing T1ρ changes solely to GAG alterations may misguide researchers and clinicians, and they encourage a more accurate understanding of the factors influencing T1ρ. [Extracted from the article]

Chondral lesions lead to degenerative changes in the surrounding cartilage tissue, increasing the risk of developing post‐traumatic osteoarthritis (PTOA). This study aimed to investigate the feasibility of quantitative magnetic resonance imaging (qMRI) for evaluation of articular cartilage in PTOA. Articular explants containing surgically induced and repaired chondral lesions were obtained from the stifle joints of seven Shetland ponies (14 samples). Three age‐matched nonoperated ponies served as controls (six samples). The samples were imaged at 9.4 T. The measured qMRI parameters included T1, T2, continuous‐wave T1ρ (CWT1ρ), adiabatic T1ρ (AdT1ρ), and T2ρ (AdT2ρ) and relaxation along a fictitious field (TRAFF). For reference, cartilage equilibrium and dynamic moduli, proteoglycan content and collagen fiber orientation were determined. Mean values and profiles from full‐thickness cartilage regions of interest, at increasing distances from the lesions, were used to compare experimental against control and to correlate qMRI with the references. Significant alterations were detected by qMRI parameters, including prolonged T1, CWT1ρ, and AdT1ρ in the regions adjacent to the lesions. The changes were confirmed by the reference methods. CWT1ρ was more strongly associated with the reference measurements and prolonged in the affected regions at lower spin‐locking amplitudes. Moderate to strong correlations were found between all qMRI parameters and the reference parameters (ρ = −0.531 to −0.757). T1, low spin‐lock amplitude CWT1ρ, and AdT1ρ were most responsive to changes in visually intact cartilage adjacent to the lesions. In the context of PTOA, these findings highlight the potential of T1, CWT1ρ, and AdT1ρ in evaluation of compositional and structural changes in cartilage. [ABSTRACT FROM AUTHOR]

In this study, we aimed to precisely localize the hyperintense signal that is generated at the osteochondral junction when using ultrashort echo time magnetic resonance imaging (MRI) and to investigate the osteochondral junction using sweep imaging with Fourier transformation (SWIFT) MRI. Furthermore, we seek to evaluate what compositional properties of the osteochondral junction are the sources of this signal. In the study, we obtained eight samples from a tibial plateau dissected from a 68‐year‐old male donor, and one additional osteochondral sample of bovine origin. The samples were imaged using high‐resolution ultrashort echo time SWIFT MRI and microcomputed tomography (μCT) scans. Localization of the bright signal in the osteochondral junction was performed using coregistered data sets. Potential sources of the signal feature were examined by imaging the bovine specimen with variable receiver bandwidths and by performing variable flip angle T1 relaxation time mapping. The results of the study showed that the hyperintense signal was found to be located entirely in the deep noncalcified articular cartilage. The intensity of this signal at the interface varied between the specimens. Further tests with bovine specimens indicated that the imaging bandwidth and T1 relaxation affect the properties of the signal. Based on the present results, the calcified cartilage has low signal intensity even in SWIFT imaging. Concomitantly, it appears that the bright signal seen in ultrashort echo time imaging resides within the noncalcified cartilage. Furthermore, the most likely sources of this signal are the rapid T1 relaxation of the deep cartilage and the susceptibility‐induced effects arising from the calcified tissues. [ABSTRACT FROM AUTHOR]

Aim: The horse joint, due to its similarity with the human joint, is the ultimate model for translational articular cartilage repair studies. This study was designed to determine the critical size of cartilage defects in the equine carpus and serve as a benchmark for the evaluation of new cartilage treatment options. Material and Methods: Circular full-thickness cartilage defects with a diameter of 2, 4, and 8 mm were created in the left middle carpal joint and similar osteochondral (3.5 mm in depth) defects in the right middle carpal joint of 5 horses. Spontaneously formed repair tissue was examined macroscopically, with MR and µCT imaging, polarized light microscopy, standard histology, and immunohistochemistry at 12 months. Results: Filling of 2 mm chondral defects was good (77.8 ± 8.5%), but proteoglycan depletion was evident in Safranin-O staining and gadolinium-enhanced MRI (T1Gd). Larger chondral defects showed poor filling (50.6 ± 2.7% in 4 mm and 31.9 ± 7.3% in 8 mm defects). Lesion filling in 2, 4, and 8 mm osteochondral defects was 82.3 ± 3.0%, 68.0 ± 4.6% and 70.8 ± 15.4%, respectively. Type II collagen staining was seen in 9/15 osteochondral defects but only in 1/15 chondral defects. Subchondral bone pathologies were evident in 14/15 osteochondral samples but only in 5/15 chondral samples. Although osteochondral lesions showed better neotissue quality than chondral lesions, the overall repair was deemed unsatisfactory because of the subchondral bone pathologies. Conclusion: We recommend classifying 4 mm as critical osteochondral lesion size and 2 mm as critical chondral lesion size for cartilage repair research in the equine carpal joint model. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate adiabatic T1ρ and T2ρ of articular cartilage in symptomatic osteoarthritis (OA) patients and asymptomatic volunteers, and to determine their association with magnetic resonance imaging (MRI)-based structural abnormalities in cartilage and bone.Materials and Methods: A total of 24 subjects (age range: 50-68 years; 12 female) were enrolled, including 12 early OA patients and 12 volunteers with normal joint function. Patients and volunteers underwent 3T MRI. T2 , adiabatic T1ρ , and T2ρ relaxation times of knee articular cartilage were measured. Proton density (PD)- and T1 -weighted MR image series were also obtained and separately evaluated for morphological changes using the MRI OA Knee Scoring (MOAKS) system. Comparisons using the Mann-Whitney nonparametric test were performed after dividing the study participants according to physical symptoms as determined by Western Ontario and McMaster Universities (WOMAC) score or presence of cartilage lesions, bone marrow lesions, or osteophytes.Results: Elevated adiabatic T1ρ and T2ρ relaxation times of articular cartilage were associated with cartilage loss (P = 0.024-0.047), physical symptoms (0.0068-0.035), and osteophytes (0.0039-0.027). Elevated adiabatic T1ρ was also associated with bone marrow lesions (0.033).Conclusion: Preliminary data suggest that elevated adiabatic T1ρ and T2ρ of cartilage are associated with morphological abnormalities of cartilage and bone, and thus may be applicable for in vivo OA research and diagnostics.Level Of Evidence: 2 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:678-689. [ABSTRACT FROM AUTHOR]

Purpose The aim of the present work was to validate and optimize adiabatic T1ρ and T2ρ mapping for in vivo measurements of articular cartilage at 3 Tesla (T). Methods Phantom and in vivo experiments were systematically performed on a 3T clinical system to evaluate the sequences using hyperbolic secant HS1 and HS4 pulses. R1ρ and R2ρ relaxation rates were studied as a function of agarose and chondroitin sulfate concentration and pulse duration. Optimal in vivo protocol was determined by imaging the articular cartilage of two volunteers and varying the sequence parameters, and successively applied in eight additional subjects. Reproducibility was assessed in phantoms and in vivo. Results Relaxation rates depended on agarose and chondroitin sulfate concentration. The sequences were able to generate relaxation time maps with pulse lengths of 8 and 6 ms for HS1 and HS4, respectively. In vivo findings were in good agreement with the phantoms. The implemented adiabatic T1ρ and T2ρ sequences demonstrated regional variation in relaxation time maps of femorotibial cartilage. Reproducibility in phantoms and in vivo was good to excellent for both adiabatic T1ρ and T2ρ. Conclusions The findings indicate that sequences are suitable for quantitative in vivo assessment of articular cartilage at 3 T. Magn Reson Med 77:1265-1275, 2017. © 2016 International Society for Magnetic Resonance in Medicine [ABSTRACT FROM AUTHOR]

ABSTRACT 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. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate multiple MRI parameters in a surgical model of osteochondrosis (OC) in goats. Methods: Focal ischemic lesions of two different sizes were induced in the epiphyseal cartilage of the medial femoral condyles of goats at 4 days of age by surgical transection of cartilage canal blood vessels. Goats were euthanized and specimens harvested 3, 4, 5, 6, 9 and 10 weeks post-op. Ex vivo MRI scans were conducted at 9.4 Tesla for mapping the T1, T2, T1ρ, adiabatic T1ρ and TRAFF relaxation times of articular cartilage, unaffected epiphyseal cartilage, and epiphyseal cartilage within the area of the induced lesion. After MRI scans, safranin O staining was conducted to validate areas of ischemic necrosis induced in the medial femoral condyles of six goats, and to allow comparison of MRI findings with the semi-quantitative proteoglycan assessment in corresponding safranin O-stained histological sections. Results: All relaxation time constants differentiated normal epiphyseal cartilage from lesions of ischemic cartilage necrosis, and the histological staining results confirmed the proteoglycan (PG) loss in the areas of ischemia. In the scanned specimens, all of the measured relaxation time constants were higher in the articular than in the normal epiphyseal cartilage, consistently allowing differentiation between these two tissues. Conclusions: Multiparametric MRI provided a sensitive approach to discriminate between necrotic and viable epiphyseal cartilage and between articular and epiphyseal cartilage, which may be useful for diagnosing and monitoring OC lesions and, potentially, for assessing effectiveness of treatment interventions. [ABSTRACT FROM AUTHOR]

Background: Understanding the pathogenesis of osteochondrosis/osteochondritis dissecans and other developmental orthopaedic diseases that are thought to occur secondary to defects in vascular supply to growth/epiphyseal cartilage has been hampered by the inability to image the vasculature in this tissue. This is particularly true in human beings due to limitations of current imaging techniques and the lack of availability of appropriate cadaveric samples for histological studies. Hypothesis: Susceptibility-weighted imaging, an MRI sequence, allows identification of characteristic differences in the vascular architecture in species that are affected by osteochondrosis/osteochondritis dissecans on the femoral condyle (humans and pigs) versus a species that is free of the disease (goat). Study Design: Controlled laboratory study. Materials: Distal femora from cadavers of juvenile humans (n = 5), pigs (n = 3), and goats (n = 3) were scanned in a 9.4-T MRI scanner using susceptibility-weighted imaging. Three-dimensional reconstructions were created, and minimum intensity projections were calculated in 3 planes to enhance visualization of the vascular architecture. Results: Susceptibility-weighted imaging allowed clear visualization of the epiphyseal vasculature in all species. Vascular architecture, with vessels primarily arising from the perichondrium, was similar in humans and pigs, which are predisposed to osteochondrosis/osteochondritis dissecans, and was starkly different from that present in goats, a species in which there are no reports of osteochondrosis/osteochondritis dissecans. Furthermore, vessels in the distal femoral predilection site disappeared with age in humans in a pattern similar to that reported previously in pigs. Conclusion: Nearly identical vascular architecture at the shared primary predilection site of osteochondrosis/osteochondritis dissecans in the femoral condyles in human beings and pigs suggests that vascular failure, which is known to be central to the pathogenesis of this disease in pigs, may also play a role in humans. Clinical Relevance: This assumption of a shared pathogenesis is supported by the pattern of disappearance of vessels with age at the primary predilection site of osteochondritis dissecans in humans, which is essentially identical to that which has been reported in pigs. Susceptibility-weighted imaging will likely help further elucidate this potential relationship in the future. [ABSTRACT FROM AUTHOR]

Various quantitative magnetic resonance imaging (qMRI) biomarkers, including but not limited to parametric MRI mapping, semiquantitative evaluation, and morphological assessment, have been successfully applied to assess cartilage repair in both animal and human studies. Through the interaction between interstitial water and constituent macromolecules the compositional and structural properties of cartilage can be evaluated. In this review a comprehensive view of a variety of quantitative techniques, particularly those involving parametric mapping, and their relationship to the properties of cartilage repair is presented. Some techniques, such as T2 relaxation time mapping and delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), are well established, while the full potential of more recently introduced techniques remain to be demonstrated. A combination of several MRI techniques is necessary for a comprehensive characterization of chondral repair. J. Magn. Reson. Imaging 2012; 36:1287-1299. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: The depth-wise variation of T2 relaxation time is known to reflect the collagen network architecture in cartilage, while the delayed Gadolinium Enhanced MRI of Cartilage (dGEMRIC) technique is sensitive to tissue proteoglycan (PG) concentration. As the cartilage PG content varies along the tissue depth, the depth-dependent accumulation of the contrast agent may affect the inherent T2 of cartilage in a nonconstant manner. Therefore, T2 and dGEMRIC are typically measured in separate MRI sessions. In the present in vitro MRI study at 9.4 T, depth-wise T2 profiles and collagenous zone thicknesses as determined from T2 maps in the absence and presence of Gd-DTPA2− (T2 and T2Gd, respectively) were compared in samples of intact human articular cartilage (n=65). These T2 measures were further correlated with birefringence (BF) of polarized light microscopy (PLM) to quantify the ability of MRI to predict the properties of the collagen fibril network. The reproducibility of the T2 measurement in the current setup was also studied. Typical tri-laminar collagen network architecture was observed both with and without Gd-DTPA2−. The inverse of BF (1/BF) correlated significantly with both T2 and T2Gd (r=0.91, slope=0.56 and r=0.90, slope=0.63), respectively. The statistically significant linear correlations between zone thicknesses as determined from T2 and T2Gd were r=0.55 (slope=0.49), r=0.74 (slope=0.71) and r=0.95 (slope=0.94) for superficial, middle and deep tissue zones, respectively. Reproducibility of the T2 measurement was worst for superficial cartilage. Consistent with PLM, T2 and T2Gd measurements reveal highly similar depth-dependent information on collagen network in intact human cartilage. Thus, dGEMRIC and T2 measurements in one MRI session are feasible for intact articular cartilage in vitro. [Copyright &y& Elsevier]

Degeneration of cartilage can be studied non-invasively with quantitative MRI. A promising parameter for detecting early osteoarthritis in articular cartilage is T 1 ρ , which can be tuned via the amplitude of the spin-lock pulse. By measuring T 1 ρ at several spin-lock amplitudes, the dispersion of T 1 ρ is obtained. The aim of this study is to find out if the dispersion contains diagnostically relevant information complementary to a T 1 ρ measurement at a single spin-lock amplitude. To this end, five differently acquired dispersion parameters are utilized; A , B , τ c , T 1 ρ /T 2 , and R 2 − R 1 ρ. An open dataset of an equine model of post-traumatic cartilage was utilized to assess the T 1 ρ dispersion parameters for the evaluation of cartilage degeneration. Firstly, the parameters were compared for their sensitivity in detecting degenerative changes. Secondly, the relationship of the dispersion parameters to histological and biomechanical reference parameters was studied. Parameters A , T 1 ρ /T 2 , and R 2 − R 1 ρ were found to be sensitive to lesion-induced changes in the cartilage within sample. Strong correlations of several dispersion parameters with optical density, as well as with collagen fibril angle were found. Most of the dispersion parameters correlated strongly with individual T 1 ρ values. The results suggest that dispersion parameters can in some cases provide a more accurate description of the biochemical composition of cartilage as compared to conventional MRI parameters. However, in most cases the information given by the dispersion parameters is more of a refinement than complementary to conventional quantitative MRI. [ABSTRACT FROM AUTHOR]

Femoroacetabular impingement (FAI) is a condition in which subtle deformities of the femoral head and acetabulum (hip socket) result in pathological abutment during hip motion. FAI is a common cause of hip pain and can lead to acetabular cartilage damage and osteoarthritis. For some patients with FAI, surgical intervention is indicated, and it can improve quality of life and potentially delay the onset of osteoarthritis. For other patients, however, surgery is contraindicated because significant cartilage damage has already occurred. Unfortunately, current imaging modalities (X-rays and conventional MRI) are subjective and lack the sensitivity to distinguish these two groups reliably. In this paper, we describe the pairing of T2* mapping data (an investigational, objective MRI sequence) and a spatial proportional odds model for surgically obtained ordinal outcomes (Beck's scale of cartilage damage). Each hip in the study is assigned its own spatial dependence parameter, and a Dirichlet process prior distribution permits clustering of said parameters. Using the fitted model, we produce a six-color, patient-specific predictive map of the entire acetabular cartilage. Such maps will facilitate patient education and clinical decision making. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: In the present work we introduced two MRI rotating frame relaxation methods, namely adiabatic T1ρ and Relaxation Along a Fictitious Field (RAFF), along with an inversion-prepared Magnetization Transfer (MT) protocol for assessment of articular cartilage. Given the inherent sensitivity of rotating frame relaxation methods to slow molecular motions that are relevant in cartilage, we hypothesized that adiabatic T1ρ and RAFF would have higher sensitivity to articular cartilage degradation as compared to laboratory frame T2 and MT. To test this hypothesis, a proteoglycan depletion model was used. Relaxation time measurements were performed at 0 and 48h in 10 bovine patellar specimens, 5 of which were treated with trypsin and 5 untreated controls were stored under identical conditions in isotonic saline for 48h. Relaxation times measured at 48h were longer than those measured at 0h in both groups. The changes in T2 and MT relaxation times after 48h were approximately 3 times larger in the trypsin treated specimens as compared to the untreated group, whereas increases of adiabatic T1ρ and RAFF were 4 to 5 fold larger. Overall, these findings demonstrate a higher sensitivity of adiabatic T1ρ and RAFF to the trypsin-induced changes in bovine patellar cartilage as compared to the commonly used T2 and MT. Since adiabatic T1ρ and RAFF are advantageous for human applications as compared to standard continuous-wave T1ρ methods, adiabatic T1ρ and RAFF are promising tools for assessing cartilage degradation in clinical settings. [Copyright &y& Elsevier]

Changes in the fibril-reinforced poroelastic (FRPE) mechanical material parameters of human patellar cartilage at different stages of osteoarthritis (OA) are not known. Further, the patellofemoral joint loading is thought to include more sliding and shear compared to other knee joint locations, thus, the relations between structural and functional changes may differ in OA. Thus, our aim was to determine the patellar cartilage FRPE properties followed by associating them with the structure and composition. Osteochondral plugs (n = 14) were harvested from the patellae of six cadavers. Then, the FRPE material properties were determined, and those properties were associated with proteoglycan content, collagen fibril orientation angle, optical retardation (fibril parallelism), and the state of OA of the samples. The initial fibril network modulus and permeability strain-dependency factor were 72% and 63% smaller in advanced OA samples when compared to early OA samples. Further, we observed a negative association between the initial fibril network modulus and optical retardation (r = -0.537, p < 0.05). We also observed positive associations between 1) the initial permeability and optical retardation (r = 0.547, p < 0.05), and 2) the initial fibril network modulus and optical density (r = 0.670, p < 0.01).These results suggest that the reduced pretension of the collagen fibrils, as shown by the reduced initial fibril network modulus, is linked with the loss of proteoglycans and cartilage swelling in human patellofemoral OA. The characterization of these changes is important to improve the representativeness of knee joint models in tissue and cell scale. [ABSTRACT FROM AUTHOR]

Finite element modelling can be used to evaluate altered loading conditions and failure locations in knee joint tissues. One limitation of this modelling approach has been experimental comparison. The aims of this proof-of-concept study were: 1) identify areas susceptible to osteoarthritis progression in anterior cruciate ligament reconstructed patients using finite element modelling; 2) compare the identified areas against changes in T 2 and T 1ρ values between 1-year and 3-year follow-up timepoints. Two patient-specific finite element models of knee joints with anterior cruciate ligament reconstruction were created. The knee geometry was based on clinical magnetic resonance imaging and joint loading was obtained via motion capture. We evaluated biomechanical parameters linked with cartilage degeneration and compared the identified risk areas against T 2 and T 1ρ maps. The risk areas identified by the finite element models matched the follow-up magnetic resonance imaging findings. For Patient 1, excessive values of maximum principal stresses and shear strains were observed in the posterior side of the lateral tibial and femoral cartilage. For Patient 2, high values of maximum principal stresses and shear strains of cartilage were observed in the posterior side of the medial joint compartment. For both patients, increased T 2 and T 1ρ values between the follow-up times were observed in the same areas. Finite element models with patient-specific geometries and motions and relatively simple material models of tissues were able to identify areas susceptible to post-traumatic knee osteoarthritis. We suggest that the methodology presented here may be applied in large cohort studies. • Patient-specific finite element models can predict location susceptible to osteoarthritis. • Assessment done for patient with anterior cruciate ligament reconstruction • Assessment done using collagen-specific and proteoglycan-specific parameters • Finite element model predictions matched magnetic resonance imaging follow-up information [ABSTRACT FROM AUTHOR]