Short TE MR Microscopy: Accurate measurement and zonal differentiation of normal hyaline cartilage

The purpose of this study was to use MR imaging to accurately measure the thickness of hyaline cartilage and determine the MR contrast parameters for differentiation of cartilage zones in normal human cartilage samples. Cartilage samples were examined using three dimensional spin-echo MR microscopy at 9.4 T with a voxel size of 31 × 31 × 300 μm. Effects of T₂ signal loss, susceptibility, and partial volume on measured thickness of cartilage were investigated. Thickness measurements were obtained on corresponding histological sections for comparison. Optimal contrast parameters for delineation of cartilage zones were evaluated using magnetization transfer, inversion recovery, T₁, and T₂ contrast. T₂ relaxation losses were identified as the primary source of discrepancy between the measured thickness of cortical bone and hyaline cartilage. Good contrast for zonal differentiation was obtained using T₁ weighting. We conclude that images obtained using short TE MR microscopy can be used to accurately measure cartilage and bone thickness in human specimens, and can demonstrate zones within normal cartilage.     

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.     

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.     

MR Spectroscopic imaging of collagen: Tendons and knee menisci

Water molecules associated with collagen have short transverse (T₂) relaxation times. Projection-reconstruction techniques are able to achieve an echo time (TE) much shorter than conventional techniques, allowing imaging of tissues with T₂ < 5 ms. Using these techniques, a conventional 1.5-T MRI human imaging system can directly image collagen-associated water from knee menisci and tendons in normal volunteers and patients. Long-T₂ suppression improves the contrast between these structures and the surrounding tissue with long-T₂ relaxation times. Spectroscopic imaging provides improved lipid/water registration and information about chemical composition and relaxation times. Direct imaging of tendons and menisci may provide more information about these structures and provide a new way to assess both injury and repair.     

1.5T MR研究健康人膝关节软骨T_2值空间分布

目的 研究健康成人膝关节软骨T2弛豫时间(T2值)空间分布.方法 1.5T场强下对21名健康男性(年龄24～39岁,平均30岁±4岁)行膝关节矢状位多回波多层面SE序列扫描,使用Profile软件测量股骨非承重软骨的前部、股骨承重软骨、胫骨承重软骨、髌软骨的T2弛豫时间(即T2值),采用方差分析检验各部位软骨深层和浅层T2值、承重软骨和非承重软骨的T2值空间分布的差异.结果 健康人膝关节软骨T2值空间分布呈浅凹形曲线,即近软骨下骨质T2值较高,随后T2值从软骨深层到浅层逐渐增高,并且各层T2值存在差异(F=70.892,P＜0.05).髌软骨T2值空间分布变化最大,股胫关节承重软骨和股骨前部非承重软骨T2值的空间分布变化较平缓.髌软骨深层T2值[(26.56±4.4) ms]明显低于所有软骨深层T2值(P=0.001).股骨外髁承重软骨浅层T2值[(35.2±6.31) ms]明显低于髌软骨[(40.78±3.56) ms]和股骨非承重软骨前部[(42.31±2.4) ms](P=0.002,P=0.000).胫骨外髁承重部软骨浅层T2值[37.11±6.6) ms]明显低于股骨非承重前部(P=0.000).结论 1.5T 场强下健康人膝关节软骨T2值具有特定空间分布,对量化研究退行性骨关节炎和其他关节病变具有参考价值.     

MR-microscopic visualization of anisotropic internal cartilage structures using the magic angle technique

NMR microscopic studies of articular cartilage at 7.1 T are presented. Using a special experimental design, T₂-weighted spin-echo images of cartilage-bone plugs were taken under variable angles with respect to the static magnetic field B_o to visualize the angular-dependent representation of internal matrix structures mediated by the collagen network arrangement. To quantify the observed orientational effect in the MR images, exact measurements of the transverse relaxation time T₂ were taken using the CPMG sequence. The NMR experiments show the strong influence of the cartilage orientation with respect to the static magnetic field on the inhomogeneous appearance of the articular cartilage in the MR image. Additionally performed polarization light microscopic investigations demonstrate the direct relation between the oriented collagenous structures and the anisotropic regions observed in the MR images. A simple cartilage matrix model derived from the experimental findings is proposed, and consequences for the clinical assessment of the articular joint are discussed.     

T1 assessment of hip joint cartilage following intra‐articular gadolinium injection: A pilot study

This pilot study defines the feasibility of cartilage assessment in symptomatic femoroacetabular impingement patients using intra‐articular delayed gadolinium‐enhanced MRI of cartilage (ia‐dGEMRIC). Nine patients were scanned preliminary to study the contrast infiltration process into hip joint cartilage. Twenty‐seven patients with symptomatic femoroacetabular impingement were subsequently scanned with intra‐articular delayed gadolinium‐enhanced MRI of cartilage. These T₁ findings were correlated to morphological findings. Zonal variations were studied. This pilot study demonstrates a significant difference between the pre‐ and postcontrast T₁ values (P < 0.001) remaining constant for 45 min. We noted higher mean T₁ values in morphologically normal‐appearing cartilage than in damaged cartilage, which was statistically significant for all zones except the anterior‐superior zone. Intraobserver (0.972) and interobserver correlation coefficients (0.933) were statistically significant. This study outlines the feasibility of intra‐articular delayed gadolinium‐enhanced MRI of cartilage for assessment of cartilage changes in patients with femoroacetabular impingement. It can also define the topographic extent and differing severities of cartilage damage. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Orientation-dependent changes in MR signal intensity of articular cartilage: a manifestation of the “magic angle” effect

Objective: To study magnetic resonance (MR) imaging pattern of normal hyaline articular cartilage in the knee joint with regard to the contribution of the “magic angle” effect to the MR signal. Design. Thirty-two healthy volunteers were imaged in a standard supine position in a 1.5-T unit using spin echo and gradient echo sequences. Nine volunteers were reimaged with the knee flexed. The signal behavior of the hyaline cartilage of the femoral condyles was evaluated qualitatively and quantitatively. The extended and flexed positions of the nine volunteers were compared. Results. A superficial and a deep hyperintense layer and a hypointense middle cartilage layer were observed. Segments of increased signal intensity were visible along the condyles; a magic angle effect on signal intensity was evident in the hypointense middle layer with both gradient echo and spin echo images. Conclusion. The MR signal behavior of hyaline cartilage is influenced by the alignment of the collagen fibers within the cartilage in relation to the magnetic field. Failure to recognize this effect may lead to inaccurate diagnosis.     

Quantitative mapping of T2 using partial spoiling

Fast quantitative MRI has become an important tool for biochemical characterization of tissue beyond conventional T₁, T₂, and T₂*‐weighted imaging. As a result, steady‐state free precession (SSFP) techniques have attracted increased interest, and several methods have been developed for rapid quantification of relaxation times using steady‐state free precession. In this work, a new and fast approach for T₂ mapping is introduced based on partial RF spoiling of nonbalanced steady‐state free precession. The new T₂ mapping technique is evaluated and optimized from simulations, and in vivo results are presented for human brain at 1.5 T and for human articular cartilage at 3.0 T. The range of T₂ for gray and white matter was from 60 msec (for the corpus callosum) to 100 msec (for cortical gray matter). For cartilage, spatial variation in T₂ was observed between deep (34 msec) and superficial (48 msec) layers, as well as between tibial (33 msec), femoral, (54 msec) and patellar (43 msec) cartilage. Excellent correspondence between T₂ values derived from partially spoiled SSFP scans and the ones found with a reference multicontrast spin‐echo technique is observed, corroborating the accuracy of the new method for proper T₂ mapping. Finally, the feasibility of a fast high‐resolution quantitative partially spoiled SSFP T₂ scan is demonstrated at 7.0 T for human patellar cartilage. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

In vivo transport of Gd-DTPA(2-) in human knee cartilage assessed by depth-wise dGEMRIC analysis

Purpose:

To investigate the transport of Gd‐DTPA^2? in different layers of femoral knee cartilage in vivo.

Materials and Methods:

T₁ measurements (1.5 Tesla) were performed in femoral knee cartilage of 23 healthy volunteers. The weight‐bearing central cartilage was analyzed before contrast and at eight time points after an intravenous injection of Gd‐DTPA^2?: 12–60 min (4 volunteers) and 1–4 h (19 volunteers). Three regions of interest were segmented manually: deep, middle, and superficial.

Results:

Before contrast injection, a depth‐wise variation of T₁ was observed with 50% higher values in the superficial region compared with the deep region. In the deep region, the uptake of Gd‐DTPA^2? was not detected until 36 min and the concentration increased until 240 min, whereas in the superficial region, the uptake was seen already at 12 min and the concentration decreased after 180 min (P < 0.01). There was a difference between medial and lateral compartment regarding bulk, but not superficial Gd‐DTPA^2? concentration. The bulk gadolinium concentration was negatively related to the cartilage thickness (r = ?0.68; P < 0.01).

Conclusion:

The depth‐wise and thickness dependent variations in Gd‐DTPA² transport influence the interpretation of bulk dGEMRIC analysis in vivo. In thick cartilage, incomplete penetration of Gd‐DTPA² will yield a falsely too long T₁. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.

     

In vivo MRI measurement of fetal blood oxygen saturation in cardiac ventricles of fetal sheep: A feasibility study

The purpose of this study was to assess the feasibility to determine fetal blood oxygen saturation (sO₂) with T₂‐weighted MR sequences using a fetal sheep model. T₂ measurements were performed on a 1.5‐T scanner using a T₂ preparation pulse in combination with a three‐dimensional balanced steady‐state free precession sequence repeated at different echo times. Eight sheep fetuses were examined during a control, hypoxic, and recovery phase to perform T₂‐weighted scans of the fetal blood in the heart. Signal intensities in the left and right ventricle were measured to calculate the MR blood sO₂. During each phase, fetal carotid artery sO₂ was directly measured and correlated with MR sO₂. A Bland‐Altman plot was performed. Fetal carotid artery sO₂ was 69% sO₂ during control, 16% sO₂ during hypoxemia, and 67% sO₂ during recovery. Mean values of the MR sO₂ were 49% sO₂ and 40% sO₂ for control, 6% sO₂ and 3% sO₂ for hypoxemia, and 51% sO₂ and 43% sO₂ for recovery in left ventricle and right ventricle, respectively. Mean values of fetal carotid artery sO₂ and MR sO₂ were highly correlated (left ventricle: r = 0.87, right ventricle: r = 0.89). According to the Bland‐Altman plot, MR sO₂ was lower compared to fetal carotid artery sO₂ (left ventricle: 15%, right ventricle: 20%). Based on our preliminary results, it seems to be possible to assess fetal sO₂ with MR oximetry. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Comparison of MRI T2 Relaxation Changes of Knee Articular Cartilage before and after Running between Young and Old Amateur Athletes

ObjectiveTo compare changes in T2 relaxation on magnetic resonance (MR) images of knee articular cartilage in younger and older amateur athletes before and after running.ResultsChanges in global cartilage T2 values after running did not differ significantly between the age groups. In terms of the depth variation, relatively higher T2 values in the older group than in the younger group were observed mainly in the superficial layers of the femoral and tibial cartilage (p < 0.05).ConclusionAge-related cartilage changes may occur mainly in the superficial layer of cartilage where collagen matrix degeneration is primarily initiated. However, no trend is observed regarding a global T2 changes between the younger and older age groups in response to exercise.     

Angle‐sensitive MRI for quantitative analysis of fiber‐network deformations in compressed cartilage

Purpose

To demonstrate the feasibility of a novel experimental method to quantitatively analyze fiber‐network deformation in compressed cartilage by angle‐sensitive magnetic resonance imaging (MRI) of cartilage.

Methods

Three knee cartilage samples of an adult sheep were imaged in a high‐resolution MRI scanner at 7 T. Main fiber orientation and its “offset” from the direction perpendicular to the bone‐cartilage boundary were derived from MR images taken at different orientations with respect to B₀. Bending of the collagen fibers was determined from weight‐bearing MRI with the load (up to 1.0 MPa) applied over the whole sample surface. A “fascicle” model of the cartilage ultrastructure was assumed to analyze characteristic intensity variations in T₂‐weighted images under load.

Results

T₂‐weighted MR images showed a strong variation of the signal intensities with sample orientation. In the T₂‐weighted weight‐bearing series, regions of high signal intensity underwent shifts from the lateral to the central parts in all three cartilage samples. The bending of the collagen fibers was determined to be 27.2°, 35.4°, and 40.0° per MPa, respectively.

Conclusion

Assuming a “fascicle” model, the presented MRI method provides quantitative measures of structural adjustments in compressed cartilage. Our preliminary analysis suggests that cartilage fiber deformation includes both bending and crimping.     

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.     

MR imaging of articular cartilage in the ankle: comparison of available imaging sequences and methods of measurement in cadavers

 Objective. To assess hyaline cartilage of cadaveric ankles using different magnetic resonance (MR) imaging techniques and various methods of measurement. Design and patients. Cartilage thicknesses of the talus and tibia were measured in ten cadaveric ankles by naked eye and by digitized image analysis from MR images of fat-suppressed T1-weighted gradient recalled (FS-SPGR), sequences and pulsed transfer saturation sequences with (FS-STS) and without fat-suppression (STS); these measurements were compared with those derived from direct inspection of cadaveric sections. The accuracy and precision errors were evaluated statistically for each imaging technique as well as measuring method. Contrast-to-noise ratios of cartilage versus joint fluid and marrow were compared for each of the imaging sequences. Results. Statistically, measurements from FS-SPGR images were associated with the smallest estimation error. Precision error of measurements derived from digitized image analysis was found to be smaller than that derived from naked eye measurements. Cartilage thickness measurements in images from STS and FS-STS sequences revealed larger errors in both accuracy and precision. Interobserver variance was larger in naked eye assessment of the cartilage. Contrast-to-noise ratio of cartilage versus joint fluid and marrow was higher with FS-SPGR than with FS-STS or STS sequences. Conclusion. Of the sequences and measurement techniques studied, the FS-SPGR sequence combined with the use of digitized image analysis provides the most accurate method for the assessment of ankle hyaline cartilage.     

Longitudinal analysis of MRI T2 knee cartilage laminar organization in a subset of patients from the osteoarthritis initiative

The purpose of this pilot study was to longitudinally quantify the T₂ laminar integrity of knee cartilage in a subset of subjects with osteoarthritis from the Osteoarthritis Initiative at baseline, 1‐year follow‐up, and 2‐year follow‐up. Cartilage from 13 subjects was divided into six compartments and subdivided into deep and superficial layers. At each time point, mean T₂ values in superficial and deep layers were compared. Longitudinal analysis included full‐thickness mean T₂, mean deep T₂, mean superficial T₂, mean T₂ laminar difference, mean percentage T₂ laminar difference, and two‐dimensional measures of cartilage thickness. More compartments showed significantly higher superficial T₂ than deep T₂ values at baseline and 1‐year follow‐up compared to 2‐year follow‐up. No significant longitudinal changes of full‐thickness mean T₂ and superficial T₂ values were observed. Significant longitudinal changes were observed in the deep T₂ values, T₂ laminar difference, and percentage T₂ laminar difference. Cartilage thickness had no influence on T₂ analysis. Results of this study suggest that laminar analysis may improve the sensitivity to detect longitudinal T₂ changes and that disruption of the T₂ laminar organization of knee cartilage may be present in knee osteoarthritis progressors. Further investigation is warranted to evaluate the potential of the presented methodology to better characterize evolution and pathophysiology of osteoarthritis. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.     

MR-based full-body preventative cardiovascular and tumor imaging: technique and preliminary experience

Recent improvements in hardware and software, lack of side effects, as well as diagnostic accuracy make magnetic resonance imaging a natural candidate for preventative imaging. Thus, the purpose of the study was to evaluate the feasibility of a comprehensive 60-min MR-based screening examination in healthy volunteers and a limited number of patients with known target disease. In ten healthy volunteers (7 men, 3 women; mean age, 32.4 years) and five patients (4 men, 1 woman; mean age, 56.2 years) with proven target disease we evaluated the performance of a comprehensive MR screening strategy by combining well-established organ-based MR examination components encompassing the brain, the arterial system, the heart, the lungs, and the colon. All ten volunteers and five patients tolerated the comprehensive MR examination well. The mean in-room time was 63 min. In one volunteer, insufficient colonic cleansing on the part of the volunteer diminished the diagnostic reliability of MR colonography. All remaining components of the comprehensive MR examination were considered diagnostic in all volunteers and patients. In the five patients, the examination revealed the known pathologies [aneurysm of the anterior communicating artery (n=1), renal artery stenosis (n=1), myocardial infarct (n=1), and colonic polyp (n=2)]. The outlined MR screening strategy encompassing the brain, the arterial system, the heart, the lung, and the colon is feasible. Further studies have to show that MR-based screening programs are cost-effective in terms of the life-years saved.     

Structure, function, and degeneration of bovine hyaline cartilage: assessment with MR imaging in vitro

The basic magnetic resonance (MR) imaging pattern of normal and degenerated hyaline articular cartilage was studied in vitro in 40 fresh bovine patellae. With the use of an ample spectrum of strongly T1- to T2-weighted sequences, two zones of cartilage with different signal intensities were observed in all specimens. A superficial cartilaginous layer in the MR image with higher water content and longer T1 and T2 correlated with the tangential and transitional zones of normal articular cartilage, whereas a second MR imaging zone with shorter T1 and T2 was identified in the depth of the articular cartilage. Different functional properties in pressure resistance were observed in the two layers. In early cartilage degeneration without thinning, there was increased hydration of the superficial cartilage layer. This study suggests that strongly T1- and T2-weighted images are indispensable for evaluating details in articular cartilage degeneration.     

Initial results of in vivo high-resolution morphological and biochemical cartilage imaging of patients after matrix-associated autologous chondrocyte transplantation (MACT) of the ankle

Objective  The aim of this study was to use morphological as well as biochemical (T2 and T2* relaxation times and diffusion-weighted imaging (DWI)) magnetic resonance imaging (MRI) for the evaluation of healthy cartilage and cartilage repair tissue after matrix-associated autologous chondrocyte transplantation (MACT) of the ankle joint. Materials and methods  Ten healthy volunteers (mean age, 32.4 years) and 12 patients who underwent MACT of the ankle joint (mean age, 32.8 years) were included. In order to evaluate possible maturation effects, patients were separated into short-term (6–13 months) and long-term (20–54 months) follow-up cohorts. MRI was performed on a 3.0-T magnetic resonance (MR) scanner using a new dedicated eight-channel foot-and-ankle coil. Using high-resolution morphological MRI, the magnetic resonance observation of cartilage repair tissue (MOCART) score was assessed. For biochemical MRI, T2 mapping, T2* mapping, and DWI were obtained. Region-of-interest analysis was performed within native cartilage of the volunteers and control cartilage as well as cartilage repair tissue in the patients subsequent to MACT. Results  The overall MOCART score in patients after MACT was 73.8. T2 relaxation times (~50 ms), T2* relaxation times (~16 ms), and the diffusion constant for DWI (~1.3) were comparable for the healthy volunteers and the control cartilage in the patients after MACT. The cartilage repair tissue showed no significant difference in T2 and T2* relaxation times (p ≥ 0.05) compared to the control cartilage; however, a significantly higher diffusivity (~1.5; p < 0.05) was noted in the cartilage repair tissue. Conclusion  The obtained results suggest that besides morphological MRI and biochemical MR techniques, such as T2 and T2* mapping, DWI may also deliver additional information about the ultrastructure of cartilage and cartilage repair tissue in the ankle joint using high-field MRI, a dedicated multichannel coil, and sophisticated sequences.     

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.