Faculty Bibliography

PURPOSE: To analyze locoregional deformation patterns indicative of contact areas in patellar cartilage after different loading exercises. MATERIALS AND METHODS: 7 healthy patellae were examined in-vivo before and immediately after standardized loading (kneeling, squatting or knee bends) and after 90 minutes of rest using a sagittal 3D-T1-w FLASH WE sequence (22 msec/ 9.8 msec/ 15 degrees / 0.3 x 0.3 x 1.5 mm(3)) at 3 T. After cartilage segmentation and 3D reconstruction, voxel-based and global precision errors (PR) were calculated. The former were used to determine significant differences in local cartilage thickness. Voxel-based 2sigma-thickness difference maps were calculated to visualize locoregional deformation patterns. Global changes in volume (Vol), mean thickness (mTh) and cartilage-bone-interface area (CBIA) were calculated. RESULTS: The voxel-based PR depended on cartilage thickness (D) ranging from 0.12 - 0.35 mm. For D >/= 1 mm the RF was < 0.31 mm (< voxel size), and for D >/= 2 mm, the RF was < 0.22 mm. The global PR was 83 mm(3) (2.4 %) for Vol, 0.06 mm (2.0 %) for mTh and 16 mm(2) (1.4 %) for CBIA. The focal cartilage deformation equaled 14 % of the local thickness reduction. The deformation areas were oval and located in the peripheral medial (more vertically oriented, all exercises) and caudo-lateral (more horizontally oriented, kneeling and knee bends) aspects of the patella and were least pronounced in knee bends. Significant changes for Vol/mTh ranged from 2.1 to 3.7 %. CONCLUSION: This MRI-based study is the first to identify in-vivo voxel-based patellar cartilage deformation patterns indicating contact and loading zones after kneeling and squatting. These zones are anatomically and functionally plausible and may represent areas where stress induced degeneration and subsequent OA can originate. The data may facilitate understanding of individual knee loading properties and help to improve and validate biomechanical models for the knee

PURPOSE: In psoriatic arthritis (PsA) multiple locations may show inflammatory changes not always readily accessible to clinical exam. Often, clinical exam is inconclusive and the decision to initiate or adapt therapy is difficult. Whole body (WB)-MRI may help in this situation by providing a comprehensive overview of affected areas/joints. The purpose of this study was to make a proof of concept whether WB-MRI in psoriatic arthritis is feasible and can provide additional information compared to clinical examination alone with regard to therapeutic decision making in patients with PsA and inconclusive clinical situation. MATERIALS AND METHODS: 30 patients with PsA and diffuse musculoskeletal pain were examined. A WB-MRI protocol was implemented on a 1.5 Tesla scanner using coronal and sagittal STIR- (TR: 5800, TE: 54, matrix 384(2) pixels, FOV 400 mm) and pre- and steady-state-post-Gadolinium-VIBE sequences (TR: 9.82, TE: 4.53, matrix 384x307 pixels, FOV: 400 mm). MRI was evaluated for image quality and inflammatory findings by two readers in consensus and compared to clinical exam. RESULTS: The WB-MR-exam was well tolerated by all patients. Image quality was rated good to excellent in 26 of 30 patients (86.6%). WB-MRI detected significantly (p<0.001) more areas of synovitis/enthesitis than clinical exam except for the hands and feet. MRI was able to detect unknown destructive bony changes in 10 patients (53%). In 22 patients (73.3%) the therapy regimen was modified, in 18 patients (62%) TNF-alpha-inhibitors were started. CONCLUSION: Whole-body MRI (WB-MRI) may be integrated in the diagnostic work-up of patients with psoriatic arthropathy facilitating individual adaptation of therapeutic strategy

Accurate techniques for simulating the deformation of soft biological tissues are an increasingly valuable tool in many areas of biomechanical analysis and medical image computing. To model the complex morphology and response of articular cartilage, a hyperviscoelastic (dispersed) fiber-reinforced constitutive model is employed to complete two specimen-specific finite element (FE) simulations of an indentation experiment, with and without considering fiber dispersion. Ultra-high field Diffusion Tensor Magnetic Resonance Imaging (17.6 T DT-MRI) is performed on a specimen of human articular cartilage before and after indentation to approximately 20% compression. Based on this DT-MRI data, we detail a novel FE approach to determine the geometry (edge detection from first eigenvalue), the meshing (semi-automated smoothing of DTI measurement voxels), and the fiber structural input (estimated principal fiber direction and dispersion). The global and fiber fabric deformations of both the un-dispersed and dispersed fiber models provide a satisfactory match to that estimated experimentally. In both simulations, the fiber fabric in the superficial and middle zones becomes more aligned with the articular surface, although the dispersed model appears more consistent with the literature. In the future, a multi-disciplinary combination of DT-MRI and numerical simulation will allow the functional state of articular cartilage to be determined in vivo

OBJECTIVES: Early research in phase-contrast imaging indicates that substantial higher soft-tissue contrast resolution can be obtained compared with conventional absorption radiography. In the present feasibility study, we used the phase contrast analyzer-based technique in tomographic mode to investigate whether structural cartilage matrix properties can be depicted in an ex vivo set-up and whether high resolution CT-phase contrast imaging may enable differentiation of osteoarthritic and intact cartilage matrixes. MATERIAL AND METHODS: Four postmortem osteochondral cylinders (7 mm diameter, 2 osteoarthritic, 2 healthy control samples from 4 human patellae) underwent tomographic phase-contrast analyzer-based imaging at high resolution (voxel size: 8(3) micron3) at 26 keV (European Synchrotron Radiation Facility, Grenoble, France). From the acquired data volumes, sets of reconstructed sagittal slices were selected at 0.5 mm increments from osteoarthritic and control specimens. Two independent, blinded observers assessed structural characteristics (cartilage thickness, topographic chondrocyte distribution homogeneity, zonal height, and surface damage) and differences between the 2 groups were determined. RESULTS: Phase contrast analyzer-based CT showed excellent depiction of the complete volume and of the 3D architecture of the cartilage in all samples. A distinct zonal pattern in the cartilage matrix could consistently be visualized. The osteoarthritic samples showed significantly lower chondrocyte distribution homogeneity (0% vs. 76% homogeneous, P < 0.001), less chondrocyte alignment (0% vs. 59% fully aligned, P < 0.001), lower height of tangential, transitional, and radial zones (all P < 0.001) and a higher prevalence of superficial cartilage damage (84% vs. 10%, P < 0.001). CONCLUSIONS: This first proof-of-concept study demonstrates that high resolution phase contrast CT visualizes structural details in relatively thick ex vivo cartilage samples. Our results suggest that the technique permits differentiation of osteoarthritic and healthy cartilage by enabling assessment of histologic characteristics of cartilage structures

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/mm(2)) 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/mm(2). A breath-hold protocol was also integrated (TR: 820 ms, TE: 58 ms, b = 0, 300 s/mm(2)). 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

Many mathematical methods have been so far proposed in order to separate absorption, refraction and ultra-small angle scattering information in phase-contrast analyzer-based images. These algorithms all combine a given number of images acquired at different positions of the crystal analyzer along its rocking curve. In this paper a comprehensive quantitative comparison between five of the most widely used phase extraction algorithms based on the geometrical optics approximation is presented: the diffraction-enhanced imaging (DEI), the extended diffraction-enhanced imaging (E-DEI), the generalized diffraction-enhanced (G-DEI), the multiple-image radiography (MIR) and the Gaussian curve fitting (GCF). The algorithms are theoretically analyzed in terms of their validity conditions and experimentally compared by using geometrical phantoms providing various amounts of absorption, refraction and scattering. The presented work shows that, due to their specific validity conditions, the considered algorithms produce results that may greatly differ, especially in the case of highly refracting and/or highly scattering materials. The various extraction algorithms are also applied to images of a human bone-cartilage sample. The aim is to validate the results obtained on geometrical phantoms and prove the efficiency of the different algorithms for applications on biological samples

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 3.0 T 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

PURPOSE: To retrospectively assess an improved quantitative methodology with separate assessment of perfusion and permeability for characterization of primary renal cell carcinoma (RCC) and monitoring antiangiogenic treatment. MATERIALS AND METHODS: Fifteen RCC patients before surgery, 6 RCC patients before and after neoadjuvant antiangiogenic therapy, and 15 patients without renal disease underwent dynamic contrast-enhanced (DCE)-MRI of the kidney with integrated retrospective respiratory triggering and an individual arterial input function. Tracer kinetic analysis was performed with a two-compartment-filtration-model for the kidney data and a two-compartment-exchange-model for the tumor data, providing four independent parameters: the perfusion-parameters plasma flow (F(P)) and plasma volume (V(P)), and the permeability-parameters extraction flow (F(E)) and extravascular-extracellular volume (V(E)). RESULTS: In tumors F(P) and F(E) were significantly lower than in normal kidneys. Tracer kinetic analysis displayed hemodynamic alteration caused by vessel infiltration or necrosis. Papillary RCC could be differentiated from clear-cell variants by a distinct perfusion pattern. In antiangiogenically treated RCC V(E) was not significantly decreased, while the perfusion parameters V(P) and F(P) were significantly diminished. CONCLUSION: DCE-MRI with integrated motion compensation enables evaluation of primary RCC and detects distinct perfusion patterns. Quantification with a two-compartment-exchange-model produces a separate perfusion- and permeability characterization and may become a diagnostic tool to monitor antiangiogenic treatment

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 (Cramer-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

PURPOSE: To evaluate the diagnostic accuracy of quantified renal perfusion parameters in identifying and differentiating renovascular from renal parenchymal disease. MATERIALS AND METHODS: In all, 27 patients underwent renal perfusion measurements on a 3.0 T magnetic resonance imaging (MRI) system. Imaging was performed with a saturation recovery TurboFLASH sequence (TR/TE 177/0.93 msec, flip angle 12 degrees , 5 slices/sec). All patients also underwent high-resolution MR angiography (MRA) (TR/TE 3.1/1.09, flip angle 23 degrees , spatial resolution 0.9 x 0.8 x 0.9 mm(3)). MR perfusion measurements were analyzed with a two-compartment model, quantifying the plasma flow (F(P))-a characteristic renal first-pass perfusion parameter. A receiver-operator characteristic analysis was used to determine the optimal threshold value for distinguishing normal and abnormal plasma flow values. Utilizing this cutoff, sensitivity and specificity of solitary MR perfusion measurements, MRA, and a diagnostic strategy combining the two were evaluated. RESULTS: Quantified MR perfusion values yielded a sensitivity of 100% and a specificity of 85% utilizing the optimal plasma flow threshold value of 150 mL/100 mL/min, whereas single MRA achieved a sensitivity of 51.9% and a specificity of 90%. Combining both methods enabled improved detection of renovascular and renoparenchymal disease with a sensitivity of 96.3% and specificity of 90%. CONCLUSION: In distinction to MRA, quantified MR perfusion measurements allow for the detection of pure renal parenchymal disorders. The combination of MRA with these perfusion measurements suggests an algorithm by which parenchymal and renovascular diseases may be reliably distinguished and the hemodynamic significance of the latter reliably determined