Christian Glaser

Magnetic Resonance Imaging-Based Assessment of Cartilage Loss in Severe Osteoarthritis Accuracy, Precision, and Diagnostic Value

OBJECTIVE To examine the in vivo accuracy and precision of magnetic resonance imaging (MRI)-based assessment of cartilage loss in patients with severe osteoarthritis (OA) of the knee. METHODS High-resolution MRI images of the tibial cartilage were obtained in 8 patients prior to total knee arthroplasty, using a water-excitation gradient-echo MRI sequence (acquisition time 6 minutes 19 seconds; spatial resolution 1.2 x 0.31 x 0.31 mm3). The MRI measurements were repeated after joint repositioning. The precision of the cartilage volume and thickness computations was determined after 3-dimensional reconstruction. During surgery, the tibial plateaus were resected, and the MRI data were compared with water displacement of surgically retrieved cartilage. RESULTS The standard deviation (coefficient of variation) of repeated tibial cartilage volume measurements was 56 mm3 (5.5%) medially and 59 mm3 (3.8%) laterally. The deviation from surgically removed tissue was -13%, on average, with a high linear correlation between both methods (r = 0.98). In patients with varus OA, the tissue loss was estimated to be 1,290 mm3 in the medial tibia and 1,150 mm3 in the lateral tibia, compared with the data in healthy volunteers. CONCLUSION Noninvasive quantitative MRI-based analysis of cartilage morphometry in severe OA is accurate, precise, and displays high potential diagnostic value.

Age-related changes in the morphology and deformational behavior of knee joint cartilage.

OBJECTIVE Alterations of cartilage morphology and mechanical properties occur in osteoarthritis, but it is unclear whether similar changes also take place physiologically during aging, in the absence of disease. In this in vivo study, we tested the hypothesis that thinning of knee joint cartilage occurs with aging and that elderly subjects display a different amount of cartilage deformation than do young subjects. METHODS We evaluated 30 asymptomatic subjects ages 50-78 years. Morphologic parameters for the knee cartilage (mean and maximum thickness, surface area) were computed from magnetic resonance imaging data. Results were compared with those in 95 young asymptomatic subjects ages 20-30 years. Deformation of the patellar cartilage was determined after the subjects performed 30 knee bends. RESULTS There was a significant reduction of patellar cartilage thickness in elderly women (-12%; P < 0.05), but not in elderly men (-6%). Femoral cartilage was significantly thinner in both sexes (-21% in women, -13% in men; P < 0.01), whereas tibial cartilage thickness displayed only nonsignificant trends (-10% in women, -7% in men). Patellar cartilage deformation was -2.6% in elderly women and -2.2% in elderly men. These values were significantly lower (P < 0.05) than those in young subjects. CONCLUSION We confirmed the hypothesis that knee cartilage becomes thinner during aging, in the absence of cartilage disease, but that the amount of reduction differs between sexes and between compartments of the knee joint. We show that under in vivo loading conditions, elderly subjects display a lower level of cartilage deformation than do healthy young subjects.

Test–retest reproducibility of the default-mode network in healthy individuals

Independent component analysis (ICA) of functional magnetic resonance imaging (fMRI) time‐series reveals distinct coactivation patterns in the resting brain representing spatially coherent spontaneous fluctuations of the fMRI signal. Among these patterns, the so‐called default‐mode network (DMN) has been attributed to the ongoing mental activity of the brain during wakeful resting state. Studies suggest that many neuropsychiatric diseases disconnect brain areas belonging to the DMN. The potential use of the DMN as functional imaging marker for individuals at risk for these diseases, however, requires that the components of the DMN are reproducible over time in healthy individuals. In this study, we assessed the reproducibility of the DMN components within and between imaging sessions in 18 healthy young subjects (mean age, 27.5 years) who were scanned three times with two resting state scans during each session at 3.0T field strength. Statistical analysis of fMRI time‐series was done using ICA implemented with BrainVoyager QX. At all three sessions the essential components of the DMN could be identified in each individual. Spatial extent of DMN activity and size of overlap within and between sessions were most reproducible for the anterior and posterior cingulate gyrus. The degree of reproducibility of the DMN agrees with the degree of reproducibility found with motor paradigms. We conclude that DMN coactivation patterns are reproducible in healthy young subjects. Therefore, these data can serve as basis to further explore the effects of aging and neuropsychiatric diseases on the DMN of the brain. Hum Brain Mapp, 2010.

High-resolution diffusion tensor imaging of human patellar cartilage: feasibility and preliminary findings.

MR diffusion tensor imaging (DTI) was used to analyze the microstructural properties of articular cartilage. Human patellar cartilage‐on‐bone samples were imaged at 9.4T using a diffusion‐weighted SE sequence (12 gradient directions, resolution = 39 × 78 × 1500 μm3). Voxel‐based maps of the mean diffusivity, fractional anisotropy (FA), and eigenvectors were calculated. The mean diffusivity decreased from the surface (1.45 × 10−3 mm2/s) to the tide mark (0.68 × 10−3 mm2/s). The FA was low (0.04–0.28) and had local maxima near the surface and in the portion of the cartilage corresponding to the radial layer. The eigenvector corresponding to the largest eigenvalue showed a distinct zonal pattern, being oriented tangentially and radially in the upper and lower portions of the cartilage, respectively. The findings correspond to current scanning electron microscopy (SEM) data on the zonal architecture of cartilage. The eigenvector maps appear to reflect the alignment of the collagenous fibers in cartilage. In view of current efforts to develop and evaluate structure‐modifying therapeutic approaches in osteoarthritis (OA), DTI may offer a tool to assess the structural properties of cartilage. Magn Reson Med 53:993–998, 2005.

Quantitative T2 mapping of matrix-associated autologous chondrocyte transplantation at 3 Tesla: an in vivo cross-sectional study.

Objectives:To evaluate magnetic resonance (MR) T2 mapping for characterization of cartilage repair tissue following matrix-associated autologous cartilage transplantation (MACT). Materials and Methods:Fifteen patients were evaluated following MACT using a 3T MR scanner. Patients were categorized into 2 postoperative intervals: I: 3–13 months, II: 19–42 months. Mean T2 relaxation times calculated from multiple spin-echo sequence were determined in regions of interest (MACT and normal hyaline cartilage) and T2 line profiles through the repair tissue and control sites were acquired. Results:Mean global T2 values of repair tissue in group I were significantly higher than at control sites (P < 0.05). Repair tissue in group II showed no significant difference to control sites. Repair tissue T2 line profiles normalized over time toward the control sites. Conclusions:T2 mapping allows visualization of cartilage repair tissue maturation. Global T2 repair tissue values approach that of control sites after more than 1.5 years, similar behavior is seen in the zonal organization.

Diffusion tensor imaging of the kidney with parallel imaging: initial clinical experience.

Objective:To evaluate the clinical feasibility of diffusion tensor imaging (DTI) of the kidney in volunteers and patients with renal diseases. Material and Methods:Ten volunteers and 22 patients (mean age, 56 ± 14.3) with renal masses and renal artery stenosis underwent breath-hold coronal fat-saturated echo-planar DTI (as provided by the manufacturer, 6 diffusion directions, diffusion weightings b = 0 and 300 s/mm2, repetition time 730 ms/echo time 72 ms; 5 slices; slice thickness, 6 mm; inplane resolution, 2.1 × 2.1 mm2; acquisition time, 26 seconds) of the kidneys at 1.5 T (MAGNETOM Avanto, Siemens Medical Solutions, Erlangen, Germany). The parallel imaging technique, generalized autocalibrating partially parallel acquisitions with an acceleration factor 2, was applied. Using the commercially available Syngo DTI task card software, regions of interests were placed in the cortex, medulla, and in renal masses if present. Fractional anisotropy (FA) and apparent diffusion coefficients (ADC) were determined, and tractography was used to visualize the renal diffusion properties. Statistical analysis was performed using the Wilcoxon signed-rank sum test and paired t tests. Results:In all volunteers, FA was significantly (P < 0.01) higher in the medulla (0.36 ± 0.03) than in the cortex (0.21 ± 0.02), whereas the ADC was significantly (P < 0.01) higher in the cortex (2.43 ± 0.19) than in the medulla (2.16 ± 0.22). Tractography typically revealed a radial preferred direction of medullary diffusion basically reflecting medullary flow. FA/ADC of simple renal cysts (n = 8) was 0.14 ± 0.05/2.86 ± 0.15. Renal cell carcinoma (n = 10) showed a wide FA range from 0.11 to 0.56. Using tractography, the structural organization of renal cell carcinoma such as pseudocapsules could be visualized. In 1 patient with unilateral high-grade renal artery stenosis, the cortical ADC of the affected kidney was lower than on the contralateral side (1.77/2.27) and the FA was increased (0.33/0.18). The FA of the medulla was increased (0.70/0.41) and the ADC decreased (1.43/1.90). Conclusions:Using parallel imaging, DTI measurements of the kidneys are feasible within a single breath-hold with good discrimination between cortex and medulla. Parallel imaging allows more slices and a superior resolution. DTI measurements of the kidney allows visualization of medullary flow, in pathology ADC and FA were altered. Further investigations will be required to evaluate the role of DTI for studying and monitoring renal ultrastructure.

Coral surface area quantification–evaluation of established techniques by comparison with computer tomography

The surface area of scleractinian corals represents an important reference parameter required for various aspects of coral reef science. However, with advancements in detection accuracy and novel approaches for coral surface area quantification, evaluation of established techniques in comparison with state-of-the-art technology gains importance to coral researchers. This study presents an evaluation of methodological accuracy for established techniques in comparison to a novel approach composed of computer tomography (CT) and 3-dimensional surface reconstruction. The skeleton surface area of reef corals from six genera representing the most common morphological growth forms was acquired by CT and subsequently measured by computer-aided 3-dimensional surface reconstruction. Surface area estimates for the same corals were also obtained by application of four established techniques: Simple and Advanced Geometry, Wax Coating and Planar Projection Photography. Comparison of the resulting area values revealed significant differences between the majority (82%) of established techniques and the CT reference. Genus-specific analysis assigned the highest accuracy to geometric approximations (Simple or Advanced Geometry) for the majority of assessed coral genera (maximum accuracy: 104%; Simple Geometry with Montipora sp.). The commonly used and invasive Wax Coating technique reached intermediate accuracy (47–74%) for the majority of genera, but performed outstanding in the measurement of branching Acropora spp. corals (maximum accuracy: 101%), while the Planar Projection Photography delivered genera-wide low accuracy (12–36%). Comparison of area values derived from established techniques and CT additionally yielded approximation factors (AFs) applicable as factors in the mathematical improvement of surface area estimates by established techniques in relation to CT reference accuracy.

T2 measurement in articular cartilage: impact of the fitting method on accuracy and precision at low SNR.

T2 relaxation time is a promising MRI parameter for the detection of cartilage degeneration in osteoarthritis. However, the accuracy and precision of the measured T2 may be substantially impaired by the low signal‐to‐noise ratio of images available from clinical examinations. The purpose of this work was to assess the accuracy and precision of the traditional fit methods (linear least‐squares regression and nonlinear fit to an exponential) and two new noise‐corrected fit methods: fit to a noise‐corrected exponential and fit of the noise‐corrected squared signal intensity to an exponential. Accuracy and precision have been analyzed in simulations, in phantom measurements, and in seven repetitive acquisitions of the patellar cartilage in six healthy volunteers. Traditional fit methods lead to a poor accuracy for low T2, with overestimations of the exact T2 up to 500%. The noise‐corrected fit methods demonstrate a very good accuracy for all T2 values and signal‐to‐noise ratio. Even more, the fit to a noise‐corrected exponential results in precisions comparable to the best achievable precisions (Cramér‐Rao lower bound). For in vivo images, the traditional fit methods considerably overestimate T2 near the bone‐cartilage interface. Therefore, using an adequate fit method may substantially improve the sensitivity of T2 to detect pathology in cartilage and change in T2 follow‐up examinations. Magn Reson Med, 2010.

MRI of the Knee at 3T: First Clinical Results With an Isotropic PDfs-Weighted 3D-TSE-Sequence

Purpose:To clinically evaluate MRI of the knee using a highly resolved isotropic fat-saturated (fs) proton-density weighted 3D-TSE-sequence (SPACE) at 3T. Materials and Methods:Imaging was performed on a 3T-scanner (Magnetom TRIO). For technical evaluation, sagittally orientated SPACE-datasets (repetition-time [TR], 1200 milliseconds/[TE], 30 milliseconds/voxel-size, 0.5 mm3/acquisition time, 10:35 minutes) were acquired from the dominant knee of 10 healthy volunteers. In the 3 major anatomic planes, 0.5, 1, and 2 mm thick reconstructions were performed. Signal-to-noise (SNR), SNR-efficiency, contrast-to-noise (CNR) ratios, and anatomic detail visualization were compared with a state-of-the-art 2D-TSE-sequence in 3 imaging planes (TR, 3200 milliseconds/TE, 30 milliseconds/acquisition time, 12:34 minutes). Sixty patients with cartilage and meniscus pathologies were examined with these techniques. Patient SPACE-datasets were assessed in 1-mm thick reconstructions. Arthroscopical correlation was available for 18 patients. Lesion detection and diagnostic confidence were assessed by 2 radiologists independently. Statistical analysis was performed using 95% confidence intervals, Wilcoxon signed rank tests, and Weighted-&kgr;. Results:SNR-efficiency of SPACE was 4 to 5 times higher than for 2D-TSE-sequences. SNR and CNR of 1-mm thick SPACE-reconstructions were comparable to 2D-TSE-sequences and provided superior visualization of small structures such as meniscal roots.Correlation with arthroscopy did not show significant differences between 2D- and 3D-sequences. One reader detected significantly more cartilage abnormalities with the 2D-TSE-sequence (131 vs. 151, P = 0.04), probably because of an unfamiliar fluid/cartilage contrast. Diagnostic confidence was significantly higher for meniscus abnormalities for SPACE for 1 reader. Intersequence-correlation was excellent (&kgr; = 0.82–0.92). Interreader-correlation was good to excellent (&kgr; = 0.71–0.80), intrareader-correlation was excellent (&kgr; = 0.90–0.92) for both sequences. Conclusions:Time-efficient 3D-TSE-imaging of the knee at 3T is feasible with adequate SNR and CNR and excellent anatomic detail visualization. Detection and visualization of meniscus and cartilage pathologies is comparable to standard 2D-TSE-sequences. 3D-TSE-sequences with consecutive multiplanar reconstruction may become a valuable component of future knee-MRI protocols.

Diffusion Tensor Imaging (DTI) of the Kidney at 3 Tesla-Feasibility, Protocol Evaluation and Comparison to 1.5 Tesla

Purpose:The purpose of this study was to evaluate the feasibility of diffusion tensor imaging of the kidney at a field strength of 3T. We assessed fractional anisotropy (FA) and apparent diffusion coefficients (ADC) of various acquisition protocols and determined the reproducibility of these measurements. FA, ADC, signal-to-noise ratios (SNR), and contrast-to-noise ratios (CNR) were compared with those acquired at 1.5T. Material and Methods:Ten healthy volunteers were examined with a respiratory-triggered echo-planar imaging sequence (TR: 1800 ms, TE: 58 ms, b = 0, 300 s/mm2) on a 3-Tesla whole-body MR scanner. Protocol variations included diffusion measurements during free-breathing, in 6 or 12 directions, and an additional b-value of 50 s/mm2. A breath-hold protocol was also integrated (TR: 820 ms, TE: 58 ms, b = 0, 300 s/mm2). Measurements with 2 b-values and 6 diffusion directions were also acquired at 1.5 T. SNR was calculated with the difference-image method. Statistical analysis was performed with Wilcoxon signed-rank tests. Intrareader correlation was assessed with weighted kappa coefficients and reproducibility with the root-mean-square-average and the Bland-Altman-method. Results:At 3T, SNR of cortex and medulla and CNR of cortex/medulla were significantly higher than at 1.5T, leading to improved corticomedullary discrimination. There were no significant FA- and ADC differences with 2 b-values and 6 diffusion directions between measurements at 1.5T and 3T. FA of the medulla was significantly higher than that of the cortex in all measurements. Tractography visualized a typical radial diffusion direction in the medulla. Best image quality was achieved with a respiratory triggered protocol with 12 acquisition directions. Measurements with 3 b-values led to decreased ADCs. Acquisition in 12 directions resulted in decreased cortical FA. FA and ADC of breath-hold and free-breathing acquisitions were significantly higher than that of the respiratory-triggered protocol. Intrareader correlation ranged from kappa 0.60 to 0.96. Variance of the respiratory-triggered protocol was smaller than that of breath-hold and free-breathing protocols. Variance was highest for medullary FA in all protocols with reproducibility coefficients ranging from 0.36 to 0.46. Conclusion:Diffusion tensor imaging of the kidney at 3T is feasible and yields significantly higher SNR and CNR. FA and ADCs do not significantly differ from 1.5T. Number of b-values influences ADC-values. Acquisitions in 12 directions provide lower cortical FA-values. We recommend a respiratory-triggered protocol because of improved image quality and reproducibility.