Dagmar Krefting

Brain Viscoelasticity Alteration in Chronic-Progressive Multiple Sclerosis

Introduction Viscoelastic properties indicate structural alterations in biological tissues at multiple scales with high sensitivity. Magnetic Resonance Elastography (MRE) is a novel technique that directly visualizes and quantitatively measures biomechanical tissue properties in vivo. MRE recently revealed that early relapsing-remitting multiple sclerosis (MS) is associated with a global decrease of the cerebral mechanical integrity. This study addresses MRE and MR volumetry in chronic-progressive disease courses of MS. Methods We determined viscoelastic parameters of the brain parenchyma in 23 MS patients with primary or secondary chronic progressive disease course in comparison to 38 age- and gender-matched healthy individuals by multifrequency MRE, and correlated the results with clinical data, T2 lesion load and brain volume. Two viscoelastic parameters, the shear elasticity μ and the powerlaw exponent α, were deduced according to the springpot model and compared to literature values of relapsing-remitting MS. Results In chronic-progressive MS patients, μ and α were reduced by 20.5% and 6.1%, respectively, compared to healthy controls. MR volumetry yielded a weaker correlation: Total brain volume loss in MS patients was in the range of 7.5% and 1.7% considering the brain parenchymal fraction. All findings were significant (P<0.001). Conclusions Chronic-progressive MS disease courses show a pronounced reduction of the cerebral shear elasticity compared to early relapsing-remitting disease. The powerlaw exponent α decreased only in the chronic-progressive stage of MS, suggesting an alteration in the geometry of the cerebral mechanical network due to chronic neuroinflammation.

The influence of physiological aging and atrophy on brain viscoelastic properties in humans.

Physiological aging of the brain is accompanied by ubiquitous degeneration of neurons and oligodendrocytes. An alteration of the cellular matrix of an organ impacts its macroscopic viscoelastic properties which can be detected by magnetic resonance elastography (MRE) – to date the only method for measuring brain mechanical parameters without intervention. However, the wave patterns detected by MRE are affected by atrophic changes in brain geometry occurring in an individuals life span. Moreover, regional variability in MRE-detected age effects is expected corresponding to the regional variation in atrophy. Therefore, the sensitivity of brain MRE to brain volume and aging was investigated in 66 healthy volunteers aged 18–72. A linear decline in whole-brain elasticity was observed (−0.75%/year, R-squareu200a=u200a0.59, p<0.001); the rate is three times that determined by volume measurements (−0.23%/year, R-squareu200a=u200a0.4, p<0.001). The highest decline in elasticity (−0.92%/year, R-squareu200a=u200a0.43, p<0.001) was observed in a region of interest placed in the frontal lobe with minimal age-related shrinkage (−0.1%, R-squareu200a=u200a0.06, pu200a=u200a0.043). Our results suggest that cerebral MRE can measure geometry-independent viscoelastic parameters related to intrinsic tissue structure and altered by age.

DICOM Image Communication in Globus-Based Medical Grids

Grid computing, the collaboration of distributed resources across institutional borders, is an emerging technology to meet the rising demand on computing power and storage capacity in fields such as high-energy physics, climate modeling, or more recently, life sciences. A secure, reliable, and highly efficient data transport plays an integral role in such grid environments and even more so in medical grids. Unfortunately, many grid middleware distributions, such as the well-known Globus Toolkit, lack the integration of the world-wide medical image communication standard Digital Imaging and Communication in Medicine (DICOM). Currently, the DICOM protocol first needs to be converted to the file transfer protocol (FTP) that is offered by the grid middleware. This effectively reduces most of the advantages and security an integrated network of DICOM devices offers. In this paper, a solution is proposed that adapts the DICOM protocol to the Globus grid security infrastructure and utilizes routers to transparently route traffic to and from DICOM systems. Thus, all legacy DICOM devices can be seamlessly integrated into the grid without modifications. A prototype of the grid routers with the most important DICOM functionality has been developed and successfully tested in the MediGRID test bed, the German grid project for life sciences.

Two-frequency driven single-bubble sonoluminescence

Sonoluminescing single bubbles driven simultaneously by two harmonic frequencies were recently reported to increase the maximum light output up to a factor of 3 with respect to single mode excitation. In this paper, experimental and numerical results on single-bubble sonoluminescence (SBSL) in an air/water system using the fundamental mode of 25 kHz and the second harmonic at 50 kHz are presented. The region of light emission is mapped in the three-dimensional parameter space spanned by the two driving pressure amplitudes and their relative phase. Good agreement was seen between measured light output, maximum bubble radius, and stability boundaries and the numerical model which is based on spherical bubble oscillations regarding diffusive and shape stability. The maximum brightness was enhanced by a factor up to 2.5 with respect to single mode SBSL. However, long-term measurements reveal great variation of the emission at fundamental mode driven SBSL and of the boost factor reached with two frequencies. The overall brightness maxima of both excitation methods within a period of several hours turn out to show little difference.

Simplified implementation of medical image processing algorithms into a grid using a workflow management system

In this paper, we describe the grid integration of medical image processing applications as grid workflows. The workflow management system is able to execute all tasks related to grid communication, such as authorization, scheduling and monitoring. It remains to the developer to make the code accessible for the workflow manager, and to define, what to do with it. Coarse-grained parallelization of processing steps for runtime reduction can easily be realized. We describe the procedure how to port the code to the grid and show exemplarily the integration of segmentation and registration algorithms for transrectal ultrasound guided prostate biopsies.

Vibration-synchronized magnetic resonance imaging for the detection of myocardial elasticity changes

Vibration synchronized magnetic resonance imaging of harmonically oscillating tissue interfaces is proposed for cardiac magnetic resonance elastography. The new approach exploits cardiac triggered cine imaging synchronized with extrinsic harmonic stimulation (f = 22.83 Hz) to display oscillatory tissue deformations in magnitude images. Oscillations are analyzed by intensity threshold‐based image processing to track wave amplitude variations over the cardiac cycle. In agreement to literature data, results in 10 volunteers showed that endocardial wave amplitudes during systole (0.13 ± 0.07 mm) were significantly lower than during diastole (0.34 ± 0.14 mm, P < 0.001). Wave amplitudes were found to decrease 117 ± 40 ms before myocardial contraction and to increase 75 ± 31 ms before myocardial relaxation. Vibration synchronized magnetic resonance imaging improves the temporal resolution of magnetic resonance elastography as it overcomes the use of extra motion encoding gradients, is less sensitive to susceptibility artifacts, and does not suffer from dynamic range constraints frequently encountered in phase‐based magnetic resonance elastography. Magn Reson Med, 2012.

Exploring workflow interoperability tools for neuroimaging data analysis

Neuroimaging is a field that benefits from distributed computing infrastructures (DCIs) to perform data processing and analysis, which is often achieved using grid workflow systems. Collaborative research in neuroimaging requires ways to facilitate exchange between different groups, in particular to enable sharing, re-use and interoperability of applications implemented as workflows. The SHIWA project provides solutions to facilitate sharing and exchange of workflows between workflow systems and DCI resources. In this paper we present and analyse how the SHIWA platform was used to implement various usage scenarios in which workflow exchange supports collaboration in neuroscience. The SHIWA platform and the implemented solutions are described and analysed from the user perspective, in this case the workflow developers and the neuroscientists. We conclude that the platform in its current form is valuable for the foreseen usage scenarios, and we identify remaining challenges concerning management of multiple credentials and data transfers across DCIs.

Visualization in Health Grid Environments: A Novel Service and Business Approach

Advanced visualization technologies are gaining major importance to allow presentation and manipulation of high dimensional data. Since new health technologies are constantly increasing in complexity, adequate information processing is required for diagnostics and treatment. Therefore, the German D-Grid initiative started to build visualization centers in 2008, which have recently been embedded into the existing compute and storage infrastructure. This paper describes an analysis of this infrastructure and the interplay with life science applications for 3D and 4D visualization and manipulation. Furthermore, the performance and business aspects regarding accounting, pricing and billing are investigated. The results show the viability and the opportunities for further optimization of this novel service approach and the possibilities for a sustainable business scenario.

Translation of bubbles subject to weak acoustic forcing and error in decoupling from volume oscillations

A microbubble in a sound wave oscillates in volume and translates unsteadily. The two motions are coupled. In large-scale simulations of the structure of bubble clouds driven by acoustic fields, it has been of significant convenience to decouple volume oscillations and translation, as an approximation. The errors of this decoupling approximation were considered in an earlier presentation [A. J. Reddy and A. J. Szeri, J. Acoust. Soc. Am. 112, 1346–1352 (2002)], in the parameter range of interest in medical ultrasound. In this work, the approximation is reexamined for a much broader range of driving frequencies and bubble sizes. Solving the equation of motion for linearly oscillating bubbles, it is found that even for weak acoustic forcing, the translation speed obtained with the decoupling approximation can be in error as much as 30% relative to the translation speed in the full equations. The error depends on the bubble size, the driving frequency, and the liquid properties. The results are presented in a...

Exploring Workflow Interoperability for Neuroimage Analysis on the SHIWA Platform

Neuroimaging is a field that benefits from distributed computing infrastructures (DCIs) to perform data processing and analysis, which is often achieved using Grid workflow systems. Collaborative research in neuroimaging requires ways to facilitate exchange between different groups, in particular to enable sharing, re-use and interoperability of applications implemented as workflows. The SHIWA project provides solutions to facilitate sharing and exchange of workflows between workflow systems and DCI resources. In this paper we present and analyse how the SHIWA Platform was used to implement various cases in which workflow exchange supports collaboration in neuroscience. The SHIWA Platform and the implemented solutions are described and analysed from a “user” perspective, in this case workflow developers and neuroscientists. We conclude that the platform in its current form is valuable for these cases, and we identify remainingxa0challenges.