A B1‐insensitive high resolution 2D T1 mapping pulse sequence for dGEMRIC of the HIP at 3 Tesla

Early detection of cartilage degeneration in the hip may help prevent onset and progression of osteoarthritis in young patients with femoroacetabular impingement. Delayed gadolinium‐enhanced MRI of cartilage is sensitive to cartilage glycosaminoglycan loss and could serve as a diagnostic tool for early cartilage degeneration. We propose a new high resolution 2D T₁ mapping saturation–recovery pulse sequence with fast spin echo readout for delayed gadolinium‐enhanced magnetic resonance imaging of cartilage of the hip at 3 T. The proposed sequence was validated in a phantom and in 10 hips, using radial imaging planes, against a rigorous multipoint saturation–recovery pulse sequence with fast spin echo readout. T₁ measurements by the two pulse sequences were strongly correlated (R² > 0.95) and in excellent agreement (mean difference = ?8.7 ms; upper and lower 95% limits of agreement = 64.5 and ?81.9 ms, respectively). T₁ measurements were insensitive to B₁₊ variation as large as 20%, making the proposed T₁ mapping technique suitable for 3 T. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Delayed gadolinium‐enhanced magnetic resonance imaging (dGEMRIC) of hip joint cartilage in femoroacetabular impingement (FAI): Are pre‐ and postcontrast imaging both necessary?

The purpose of this study was to assess if delayed gadolinium MRI of cartilage using postcontrast T₁ (T_1Gd) is sufficient for evaluating cartilage damage in femoroacetabular impingement without using noncontrast values (T₁₀). T_1Gd and ΔR₁ (1/T_1Gd ? 1/T₁₀) that include noncontrast T₁ measurements were studied in two grades of osteoarthritis and in a control group of asymptomatic young‐adult volunteers. Differences between T_1Gd and ΔR₁ values for femoroacetabular impingement patients and volunteers were compared. There was a very high correlation between T_1Gd and ΔR₁ in all study groups. In the study cohort with Tonnis grade 0, correlation (r) was ?0.95 and ?0.89 with Tonnis grade 1 and ?0.88 in asymptomatic volunteers, being statistically significant (P < 0.001) for all groups. For both T_1Gd and ΔR₁, a statistically significant difference was noted between patients and control group. Significant difference was also noted for both T_1Gd and ΔR₁ between the patients with Tonnis grade 0 osteoarthritis and those with grade 1 changes. Our results prove a linear correlation between T_1Gd and ΔR₁, suggesting that T_1Gd assessment is sufficient for the clinical utility of delayed gadolinium MRI of cartilage in this setting and additional time‐consuming T₁₀ evaluation may not be needed. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Variable flip angle‐based fast three‐dimensional T1 mapping for delayed gadolinium‐enhanced MRI of cartilage of the knee: Need for B1 correction

Delayed gadolinium‐enhanced MRI of cartilage is a technique, which involves T₁ mapping to identify changes in the structural integrity of cartilage associated with osteoarthritis. Currently, the gold standard is 2D inversion recovery turbo spin echo, which suffers from long acquisition times and limited coverage. Three‐dimensional variable flip angle (VFA) is an alternate technique, which has been shown to be accurate when an estimate of T₁ is available a priori. This study validates the variable flip angle method for delayed gadolinium‐enhanced MRI of cartilage of the femoro‐tibial knee cartilage. When amplitude of (excitation) radiofrequency field inhomogeneities were minimized using nonselective pulses and amplitude of (excitation) radiofrequency field correction using an additional acquisition of a amplitude of (excitation) radiofrequency field map, the accuracy of T₁ measurements were improved, and slice‐to‐slice variations over the 3D volume were minimized. In conclusion, fast 3D T₁ mapping using the variable flip angle method with amplitude of (excitation) radiofrequency field correction appears to be an efficient and accurate method for delayed gadolinium‐enhanced MRI of cartilage of the knee. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

Feasibility of T mapping for the evaluation of hip joint cartilage at 1.5T using a three‐dimensional (3D), gradient‐echo (GRE) sequence: A prospective study

This study defines the feasibility of utilizing three‐dimensional (3D) gradient‐echo (GRE) MRI at 1.5T for T mapping to assess hip joint cartilage degenerative changes using standard morphological MR grading while comparing it to delayed gadolinium‐enhanced MRI of cartilage (dGEMRIC). MRI was obtained from 10 asymptomatic young adult volunteers and 33 patients with symptomatic femoroacetabular impingement (FAI). The protocol included T mapping without gadolinium‐enhancement utilizing a 3D‐GRE sequence with six echoes, and after gadolinium injection, routine hip sequences, and a dual‐flip‐angle 3D‐GRE sequence for dGEMRIC T₁ mapping. Cartilage was classified as normal, with mild changes, or with severe degenerative changes based on morphological MRI. T₁ and T findings were subsequently correlated. There were significant differences between volunteers and patients in normally‐rated cartilage only for T₁ values. Both T₁ and T values decreased significantly with the various grades of cartilage damage. There was a statistically significant correlation between standard MRI and T (T₁) (P < 0.05). High intraclass correlation was noted for both T₁ and T. Correlation factor was 0.860 to 0.954 (T‐T₁ intraobserver) and 0.826 to 0.867 (T‐T₁ interobserver). It is feasible to gather further information about cartilage status within the hip joint using GRE T mapping at 1.5T. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Influence of knee positions on T2, T*2, and dGEMRIC mapping in porcine knee cartilage

We examined the influence of flexed knee positions on cartilage MR assessments. Sagittal T₂, T*₂, and delayed gadolinium‐enhanced MRI of cartilage (dGEMRIC) maps of the femoral cartilage were obtained in eight 6‐month‐old porcine femorotibial joints in the extended knee position (position A: flexion 0° and femoral shaft in parallel with the amplitude of static field), flexed knee position (position B: flexion 40° and femoral shaft oriented at 40° to the amplitude of static field), and oblique‐placed knee‐extended position (position C: flexion 0° and femoral shaft oriented at 40° to the amplitude of static field). Comparison of the MR parameters between positions A and C showed isolated influence of the magic‐angle effect, and comparison between positions A and B showed effects of knee flexion. Proteoglycan and hydroxyproline content in cartilage specimen at each region of interest had no significant correlation with T₂, T*₂, and dGEMRIC values. At the central zone, located on a weight‐bearing area and parallel to the amplitude of static field, T₂/T*₂/dGEMRIC values increased by 6.8/11/0.8% at position C and by 24/44/31% at position B compared with position A. There was a significant increase in T₂ and T*₂ values at position B compared with those at position A. The substantial changes in T₂, T*₂, and dGEMRIC were shown in response to knee flexion, presumably due to the compounding influence of the magic‐angle effect and change in the intra‐articular biomechanical condition. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

In vivo MRI of fresh stored osteochondral allograft transplantation with delayed gadolinium‐enhanced MRI of cartilage: Protocol considerations and recommendations

The protocol for delayed gadolinium‐enhanced MRI of cartilage (dGEMRIC) was adapted for the evaluation of transplanted osteochondral allograft cartilage. Eight patients with focal grade 4 cartilage defects of the femoral condyle were treated with single cylindrical osteochondral allografts. At 1 and 2 years, dGEMRIC image sequences were acquired and regions of interest (ROIs) were drawn in repair and native control cartilage. Mean T₁ values of region of interest were used to calculate established dGEMRIC metrics. The correlation was measured between the ΔR₁ and R₁‐Post metrics for repair and native cartilage. T₁ times were measured in deep and superficial zones of cartilage. A strong correlation was identified between full‐thickness, deep, and superficial ΔR₁ and R₁‐Post values for native cartilage and repair cartilage for all years (range: 0.893–1.0). The mean T₁ times and ΔR₁ rate between deep and superficial regions of articular cartilage were statistically different for all regions of the distal femora analyzed at 1 year and 2 years after osteochondral allograft transplantation (P < 0.05). The dGEMRIC pre‐Gadolinium scan is unnecessary when evaluating transplanted osteochondral allograft cartilage. The observation of stratified T₁ and ΔR₁ values indicates a need to re‐evaluate the methodology behind the placement of region of interest in dGEMRIC. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Delayed contrast‐enhanced MRI of cartilage: Comparison of nonionic and ionic contrast agents

The objective of this study was to evaluate if cartilage fixed charge density is the only factor determining the distribution of the measured delayed gadolinium‐enhanced magnetic resonance imaging of cartilage index, T₁(Gd‐DTPA^2?), across cartilage in the clinical delayed gadolinium‐enhanced magnetic resonance imaging of cartilage protocol. Nineteen subjects with osteoarthritis and 14 controls were included. Cartilage T₁(Gd) was measured following administration of 0.2 mmol kg^?1 of nonionic (Gd‐DTPA‐BMA) and, at a different date, anionic (Gd‐DTPA^2?). T₁(Gd‐DTPA‐BMA) was plotted against T₁(Gd‐DTPA^2?); a slope of 0 would indicate domination by charge effects; a nonzero slope would suggest that other factors influence T₁(Gd‐DTPA‐BMA), and hence potentially T₁(Gd‐DTPA^2?). The low slope of the curve found in osteoarthritis subjects (0.31) indicates that Gd‐DTPA‐BMA penetrated most osteoarthritis cartilage to the same extent, and T₁(Gd‐DTPA‐BMA) did not differentiate cartilages, which were differentiated by T₁(Gd‐DTPA^2?). The higher slopes in control subjects (0.88) are possibly due to inhibited transport of contrast agent into healthier cartilage, potentially exaggerated by the fast body clearance of the nonionic contrast agent. Overall, the use of anionic Gd‐DTPA^2? for delayed gadolinium‐enhanced magnetic resonance imaging of cartilage is indicated for better discrimination of the health status of cartilage. Future studies could be designed to use contrast‐enhanced dynamics to understand the transport properties of tissues in the joint and to evaluate the concentration of tissue constituents. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Strain‐dependent T1 relaxation profiles in articular cartilage by MRI at microscopic resolutions

To investigate the dependency of T₁ relaxation on mechanical strain in articular cartilage, quantitative magnetic resonance T₁ imaging experiments were carried out on cartilage before/after the tissue was immersed in gadolinium contrast agent and when the tissue was being compressed (up to ～48% strains). The spatial resolution across the cartilage depth was 17.6 μm. The T₁ profile in native tissue (without the presence of gadolinium ions) was strongly strain‐dependent, which is also depth‐dependent. At the modest strains (e.g., 14% strain), T₁ reduced by up to 68% in the most surface portion of the tissue. Further compression (e.g., 45% strain) reduced T₁ mostly in the middle and deep portions of the tissue. For the gadolinium‐immersed tissue, both modest and heavy compressions (up to 48% strain) increased T₁ slightly but significantly, although the overall shapes of the T₁ profiles remained approximately the same regardless of the amount of strains. The complex relationships between the T₁ profiles and the mechanical strains were a direct consequence of the depth‐dependent proteoglycan concentration in the tissue, which determined the tissue's mechanical properties. This finding has potential implications in the use of gadolinium contrast agent in clinical magnetic resonance imaging of cartilage (the dGEMRIC procedure), when the loading or loading history of patients is considered. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

The impact of the relaxivity definition on the quantitative measurement of glycosaminoglycans in cartilage by the MRI dGEMRIC method

The relaxivities (R‐values) of the gadolinium diethylene triamine pentaacetic acid (Gd(DTPA)^2?) ions in a series of skim‐milk solutions at 0–40% milk concentrations were measured using NMR spectroscopy. The R‐value was found to be approximately linearly proportional to the concentration of the solid component in the milk solution. Using the R‐value at 20% solid component (approximately the solid concentration in bovine nasal cartilage), the glycosaminoglycan concentration in bovine nasal cartilage can be quantified using the MRI delayed gadolinium‐enhanced MRI of cartilage method without the customary scaling factor of 2. This finding is also supported by the measurements using ²³Na NMR spectroscopy, ²³Na inductively coupled plasma analysis, and biochemical assay. The choice of the R‐value definition in the MRI delayed gadolinium‐enhanced MRI of cartilage method is discussed, and the definition of Gd(DTPA)^2? ions as “millimole per volume of tissue (or milk solution for substitution)” should be used. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Quantitative cartilage degeneration associated with spontaneous osteoarthritis in a guinea pig model

Purpose:

To determine (i) the feasibility and intra‐ and inter‐scan reproducibility of T_1ρ MRI in assessing cartilage degeneration in a guinea pig model with naturally occurring joint disease that closely mimics human osteoarthritis (OA), (ii) demonstrate the sensitivity of T_1ρ MRI in assessing the age dependent cartilage degeneration in OA progression as compared to histopathological changes.

Materials and Methods:

Duncan‐Hartley guinea pigs were obtained at various ages and maintained under an IACUC approved protocol. The left hind stifle joint was imaged using T_1ρ MRI on a 9.4 Tesla Varian horizontal 20 cm bore scanner using a custom surface coil. Reproducibility of T_1ρ MRI was assessed using 4‐month‐old guinea pigs (N = 3). Three age cohorts; 3 month (N = 8), 5 month (N = 6), and 9 month (N = 5), were used to determine the age‐dependent osteoarthritic changes as measured by T_1ρ MRI. Validation of age‐dependent cartilage degeneration was confirmed by histology and Safranin‐O staining.

Results:

T_1ρ values obtained in the cartilage of the stifle joint in guinea pigs were highly reproducible with an inter‐scan mean coefficient of variation (CV) of 6.57% and a maximum intra‐scan CV of 9.29%. Mean cartilage T_1ρ values in animals with late stage cartilage degeneration were 56.3–56.9 ms (5–9 month cohorts) were both significantly (P < 0.01) higher than that obtained from 3‐month‐old cohort (44 ms) demonstrating an age‐dependent variation. T_1ρ was shown to be significantly greater than T₂. T_1ρ dispersion was observed in this animal model for the first time showing an increase of 45% between 500 Hz and 1500 Hz spin‐locking frequency. Cartilage thickness measurements were calculated from single mid‐coronal histology sections from same animals used for T_1ρ MRI. Thickness calculations showed insignificant differences between 3‐ and 5‐month cohorts and was significantly decreased by 9 months of age (P < 0.01). A moderate correlation (R² = 0.45) existed between T_1ρ values and signal intensity of Safranin‐O stain.

Conclusion:

The data presented demonstrate that T_1ρ MRI is highly reproducible in this spontaneous model of OA and may serve as a noninvasive tool to characterize joint cartilage degeneration during OA. Age‐dependent changes, verified with histological measurements of proteoglycan loss, correlated with T_1ρ across different age groups. T_1ρ has adequate dynamic range and is sensitive to detect and track the progression of cartilage degeneration in the guinea pig model before gross anatomical changes such as cartilage thinning has occurred. This study presents a technological advancement that would permit longitudinal studies of evaluating disease‐modifying therapies useful for treating human OA. J. Magn. Reson. Imaging 2012;35:891–898. © 2011 Wiley Periodicals, Inc.     

T1ρ MRI quantification of arthroscopically confirmed cartilage degeneration

Nine asymptomatic subjects and six patients underwent T₁ρ MRI to determine whether Outerbridge grade 1 or 2 cartilage degeneration observed during arthroscopy could be detected noninvasively. MRI was performed 2‐3 months postarthroscopy, using sagittal T₁‐weighted and axial and coronal T₁ρ MRI, from which spatial T₁ρ relaxation maps were calculated from segmented T₁‐weighted images. Median T₁ρ relaxation times of patients with arthroscopically documented cartilage degeneration and asymptomatic subjects were significantly different (P < 0.001), and median T₁ρ exceeded asymptomatic articular cartilage median T₁ρ by 2.5 to 9.2 ms. In eight observations of mild cartilage degeneration at arthroscopy (Outerbridge grades 1 and 2), mean compartment T₁ρ was elevated in five, but in all observations, large foci of increased T₁ρ were observed. It was determined that T₁ρ could detect some, but not all, Outerbridge grade 1 and 2 cartilage degeneration but that a larger patient population is needed to determine the sensitivity to these changes. Magn Reson Med 63:1376–1382, 2010. © 2010 Wiley‐Liss, Inc.     

Reduction of residual dipolar interaction in cartilage by spin‐lock technique

The influence of radiofrequency (RF) spin‐lock pulse on the laminar appearance of articular cartilage in MR images was investigated. Spin‐lock MRI experiments were performed on bovine cartilage plugs on a 4.7 Tesla small‐bore MRI scanner, and on human knee cartilage in vivo on a 1.5 Tesla clinical scanner. When the normal to the surface of cartilage was parallel to B₀, a typical laminar appearence was exhibited in T₂‐weighted images of cartilage plugs, but was absent in T_1ρ‐weighted images of the same plugs. At the “magic angle” orientation (when the normal to the surface of cartilage was 54.7° with respect to B₀), neither the T₂ nor the T_1ρ images demonstrated laminae. At the same time, T_1ρ values were greater than T₂ at both orientations throughout the cartilage. T_1ρ dispersion (i.e., the dependence of the relaxation rate on the spin‐lock frequency ω₁) was observed, which reached a steady‐state value of close to 2 kHz in both parallel and magic‐angle orientations. These results suggest that residual dipolar interaction from motionally‐restricted water and relaxation processes, such as chemical exchange, contribute to T_1ρ dispersion in cartilage. Further, one can reduce the laminar appearance in human articular cartilage by applying spin‐lock RF pulses, which may lead to a more accurate diagnosis of degenerative changes in cartilage. Magn Reson Med 52:1103–1109, 2004. © 2004 Wiley‐Liss, Inc.     

Multicomponent T2* mapping of knee cartilage: Technical feasibility ex vivo

Disorganization of collagen fibers is a sign of early‐stage cartilage degeneration in osteoarthritic knees. Water molecules trapped within well‐organized collagen fibrils would be sensitive to collagen alterations. Multicomponent effective transverse relaxation (T₂*) mapping with ultrashort echo time acquisitions is here proposed to probe short T₂ relaxations in those trapped water molecules. Six human tibial plateau explants were scanned on a 3T MRI scanner using a home‐developed ultrashort echo time sequence with echo times optimized via Monte Carlo simulations. Time constants and component intensities of T₂* decays were calculated at individual pixels, using the nonnegative least squares algorithm. Four T₂*‐decay types were found: 99% of cartilage pixels having mono‐, bi‐, or nonexponential decay, and 1% showing triexponential decay. Short T₂* was mainly in 1‐6 ms, while long T₂* was ～22 ms. A map of decay types presented spatial distribution of these T₂* decays. These results showed the technical feasibility of multicomponent T₂* mapping on human knee cartilage explants. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Photoreceptor degeneration changes magnetic resonance imaging features in a mouse model of retinitis pigmentosa

Retinal degeneration‐1 (rd1) mice are animal models of retinitis pigmentosa, a blinding disease caused by photoreceptor cell degeneration. This study aims to determine magnetic resonance imaging (MRI) changes in retinas of 1‐ and 3‐month‐old rd1 mice. Apparent diffusion coefficient in retina was measured using diffusion MRI. The blood‐retinal barrier leakage was evaluated using gadolinium‐diethylenetriaminepentaacetic acid‐enhanced T₁‐weighted MRI before and after systemic gadolinium‐diethylenetriaminepentaacetic acid injection. Photoreceptor degeneration in rd1 retina was apparent by decreased retinal thickness and loss of water diffusion anisotropy in both 1‐ and 3‐month‐old rd1 mice. Furthermore, statistically significant increase of mean retinal apparent diffusion coefficient and gadolinium‐diethylenetriaminepentaacetic acid‐enhanced T₁‐weighted MRI signals were observed in 3‐month‐old rd1 mice comparing with age‐matched wild‐type mice. Together, these data suggest that MRI parameter changes can signature common pathological changes in photoreceptor‐degenerated eyes, particularly blood‐retinal barrier leakage‐induced retinal edema. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Fat‐water separated delayed hyperenhanced myocardial infarct imaging

Fat deposition associated with myocardial infarction (MI) has been reported as a commonly occurring phenomenon. Magnetic resonance imaging (MRI) has the ability to efficiently detect MI using T₁‐sensitive contrast‐enhanced sequences and fat via its resonant frequency shift. In this work, the feasibility of fat‐water separation applied to the conventional delayed hyperenhanced (DHE) MI imaging technique is demonstrated. A three‐point Dixon acquisition and reconstruction was combined with an inversion recovery gradient‐echo pulse sequence. This allowed fat‐water separation along with T₁ sensitive imaging after injection of a gadolinium contrast agent. The technique is demonstrated in phantom experiments and three subjects with chronic MI. Areas of infarction were well defined as conventional hyperenhancement in water images. In two cases, fatty deposition was detected in fat images and confirmed by precontrast opposed‐phase imaging. Magn Reson Med 60:503–509, 2008. © 2008 Wiley‐Liss, Inc.     

T1ρ MRI of human musculoskeletal system

Magnetic resonance imaging (MRI) offers the direct visualization of the human musculoskeletal (MSK) system, especially all diarthrodial tissues including cartilage, bone, menisci, ligaments, tendon, hip, synovium, etc. Conventional MRI techniques based on T₁‐ and T₂‐weighted, proton density (PD) contrast are inconclusive in quantifying early biochemically degenerative changes in MSK system in general and articular cartilage in particular. In recent years, quantitative MR parameter mapping techniques have been used to quantify the biochemical changes in articular cartilage, with a special emphasis on evaluating joint injury, cartilage degeneration, and soft tissue repair. In this article we focus on cartilage biochemical composition, basic principles of T_1ρ MRI, implementation of T_1ρ pulse sequences, biochemical validation, and summarize the potential applications of the T_1ρ MRI technique in MSK diseases including osteoarthritis (OA), anterior cruciate ligament (ACL) injury, and knee joint repair. Finally, we also review the potential advantages, challenges, and future prospects of T_1ρ MRI for widespread clinical translation. J. Magn. Reson. Imaging 2015;41:586–600. © 2014 Wiley Periodicals, Inc.     

T1 mapping of the gadolinium‐enhanced myocardium: Adjustment for factors affecting interpatient comparison

Quantitative T₁ mapping of delayed gadolinium‐enhanced cardiac magnetic resonance imaging has shown promise in identifying diffuse myocardial fibrosis. Despite careful control of magnetic resonance imaging parameters, comparison of T₁ times between different patients may be problematic because of patient specific factors such as gadolinium dose, differing glomerular filtration rates, and patient specific delay times. In this work, a model driven approach to account for variations between patients to allow for comparison of T₁ data is provided. Kinetic model parameter values were derived from healthy volunteer time‐contrast curves. Correction values for the factors described above were used to normalize T₁ values to a matched state. Examples of pre‐ and postcorrected values for a pool of normal subjects and in a patient cohort of type 1 diabetic patients shows tighter clustering and improved discrimination of disease state. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

延迟Gd-DTPA增强MR软骨成像:全关节软骨成像的可行性分析

目的：探讨多层IR-TSE和可变翻转角三维FLASH序列实现全关节软骨t1值测量的可行性。材料和方法：针对模型（不同浓度的稀释Gd-DTPA溶液）和离体牛软骨,分别利用多层IR-TSE和可变翻转角三维FLASH序列进行t1值测量。以单层IR-TSE测量结果为参照标准,验证上述两种技术的可行性。结果：在模型中,多层IR-TSE与单层IR-TSE测量值的相关系数为1.000（P〈0.001）;三维FLASH与单层IR-TSE测量值的相关系数为0.997（P〈0.001）。在离体牛软骨延迟钆增强MR软骨成像中,单层IR-TSE、多层IR-TSE和三维FLASH均显示胰蛋白酶处理侧软骨的t1值显著低于对照侧软骨。多层IR-TSE与单层IR-TSE相比较,对照侧、处理侧和总体软骨t1值的相关系数分别为0.821（P=0.012）、0.968（P=0.001）和0.953（P=0.001）;三维FLASH与单层IR-TSE相比较,对照侧、处理侧和总体软骨t1值的相关系数分别为0.199（P=0.637）、0.757（P=0.030）和0.755（P=0.001）。结论：多层IR-TSE和可变翻转角三维FLASH序列均可用于全关节软骨的t1值测量。     

Further studies on the anisotropic distribution of collagen in articular cartilage by μMRI

To further study the anisotropic distribution of the collagen matrix in articular cartilage, microscopic magnetic resonance imaging experiments were carried out on articular cartilages from the central load‐bearing area of three canine humeral heads at 13 μm resolution across the depth of tissue. Quantitative T₂ images were acquired when the tissue blocks were rotated, relative to B₀, along two orthogonal directions, both perpendicular to the normal axis of the articular surface. The T₂ relaxation rate (R₂) was modeled, by three fibril structural configurations (solid cone, funnel, and fan), to represent the anisotropy of the collagen fibrils in cartilage from the articular surface to the cartilage/bone interface. A set of complex and depth‐dependent characteristics of collagen distribution was found in articular cartilage. In particular, there were two anisotropic components in the superficial zone and an asymmetrical component in the radial zone of cartilage. A complex model of the three‐dimensional fibril architecture in articular cartilage is proposed, which has a leaf‐like or layer‐like structure in the radial zone, arises in a radial manner from the subchondral bone, spreads and arches passing the isotropic transitional zone, and exhibits two distinct anisotropic components (vertical and transverse) in the surface portion of the tissue. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

Relaxation anisotropy in cartilage by NMR microscopy (μMRI) at 14-μm resolution

To study the structural anisotropy and the magic-angle effect in articular cartilage, T₁, and T₂ images were constructed at a series of orientations of cartilage specimens in the magnetic field by using NMR microscopy (μMRI). An isotropic T₁, and a strong anisotropic T₂ were observed across the cartilage tissue thickness. Three distinct regions in the microscopic MR images corresponded approximately to the superficial, transitional, and radial histological zones in the cartilage. The percentage decrease of T₂ follows the pattern of the curve of (3cos²θ ? 1)² at the radial zone, where the collagen fibrils are perpendicular to the articular surface. In contrast, little orientational dependence of T₂ was observed at the transitional zone, where the collagen fibrils are more randomly oriented. The result suggests that the interactions between water molecules and proteoglycans have a directional nature, which is somehow influenced by collagen fibril orientation. Hence, T₂ anisotropy could serve as a sensitive and noninvasive marker for molecular-level orientations in articular cartilage.