Comparing isotropic and anisotropic smoothing for voxel-based DTI analyses: A simulation study.

Voxel-based analysis (VBA) methods are increasingly being used to compare diffusion tensor image (DTI) properties across different populations of subjects. Although VBA has many advantages, its results are highly dependent on several parameter settings, such as those from the coregistration technique applied to align the data, the smoothing kernel, the statistics, and the post-hoc analyses. In particular, to increase the signal-to-noise ratio and to mitigate the adverse effect of residual image misalignments, DTI data are often smoothed before VBA with an isotropic Gaussian kernel with a full width half maximum up to 16 x 16 x 16 mm(3).

A diffusion tensor imaging group study of the spinal cord in multiple sclerosis patients with and without T2 spinal cord lesions.

Purpose: To examine the T(2)-normal appearing spinal cord of patients with multiple sclerosis (MS) using diffusion tensor imaging.

Materials And Methods: Diffusion tensor images of the spinal cord were acquired from 21 healthy subjects, 11 MS patients with spinal cord lesions, and 10 MS patients without spinal cord lesions on the T(2)-weighted MR images. Different diffusion measures were evaluated using both a region of interest (ROI) -based and a diffusion tensor tractography-based segmentation approach.

Quantitative diffusion tensor imaging in amyotrophic lateral sclerosis: revisited.

Voxel-based analyses (VBA) are increasingly being used to detect white matter abnormalities with diffusion tensor imaging (DTI) in different types of pathologies. However, the validity, specificity, and sensitivity of statistical inferences of group differences to a large extent depend on the quality of the spatial normalization of the DTI images. Using high-dimensional nonrigid coregistration techniques that are able to align both the spatial and orientational diffusion information and incorporate appropriate templates that contain this complete DT information may improve this quality.

Diffusion tensor imaging in a rat model of Parkinson's disease after lesioning of the nigrostriatal tract.

Parkinson's disease (PD) is characterised by degeneration of the nigrostrial connection causing dramatic changes in the dopaminergic pathway underlying clinical pathology. Till now, no MRI tools were available to follow up any specific PD-related neurodegeneration. However, recently, diffusion tensor imaging (DTI) has received considerable attention as a new and potential in vivo diagnostic tool for various neurodegenerative diseases.

The B-matrix must be rotated when correcting for subject motion in DTI data.

To estimate diffusion tensor MRI (DTI) measures, such as fractional anisotropy and fiber orientation, reliably, a large number of diffusion-encoded images is needed, preferably cardiac gated to reduce pulsation artifacts. However, the concomitant longer acquisition times increase the chances of subject motion adversely affecting the estimation of these measures. While correcting for motion artifacts improves the accuracy of DTI, an often overlooked step in realigning the images is to reorient the B-matrix so that orientational information is correctly preserved.

On the construction of a ground truth framework for evaluating voxel-based diffusion tensor MRI analysis methods.

Although many studies are starting to use voxel-based analysis (VBA) methods to compare diffusion tensor images between healthy and diseased subjects, it has been demonstrated that VBA results depend heavily on parameter settings and implementation strategies, such as the applied coregistration technique, smoothing kernel width, statistical analysis, etc. In order to investigate the effect of different parameter settings and implementations on the accuracy and precision of the VBA results quantitatively, ground truth knowledge regarding the underlying microstructural alterations is required. To address the lack of such a gold standard, simulated diffusion tensor data sets are developed, which can model an array of anomalies in the diffusion properties of a predefined location.

Iterative co-linearity filtering and parameterization of fiber tracts in the entire cingulum.

We present a method for the fully automated extraction of the cingulum using diffusion tensor imaging (DTI) data. We perform whole-brain tractography and initialize tract selection in the cingulum with a registered DTI atlas. Tracts are parameterized from which tract co-linearity is derived.

On the construction of an inter-subject diffusion tensor magnetic resonance atlas of the healthy human brain.

Voxel based morphometry (VBM) has been increasingly applied to detect diffusion tensor (DT) image abnormalities in patients for different pathologies. An important requisite for a robust VBM analysis is the availability of a high-dimensional non-rigid coregistration technique that is able to align both the spatial and the orientational DT information. Consequently, there is a need for an inter-subject DTI atlas as a group specific reference frame that also contains this orientational DT information.

A tracking-based diffusion tensor imaging segmentation method for the detection of diffusion-related changes of the cervical spinal cord with aging.

Purpose: To compare region of interest (ROI)-based and diffusion tensor tractography (DTT)-based methods for evaluating diffusion properties of the spinal cord as a function of age.

Materials And Methods: Commonly, an ROI segmentation is used to delineate the spinal cord. In this work, new segmentation methods are developed based on DTT.

Microstructural maturation of the human brain from childhood to adulthood.

Brain maturation is a complex process that continues well beyond infancy, and adolescence is thought to be a key period of brain rewiring. To assess structural brain maturation from childhood to adulthood, we charted brain development in subjects aged 5 to 30 years using diffusion tensor magnetic resonance imaging, a novel brain imaging technique that is sensitive to axonal packing and myelination and is particularly adept at virtually extracting white matter connections. Age-related changes were seen in major white matter tracts, deep gray matter, and subcortical white matter, in our large (n=202), age-distributed sample.

Nonrigid coregistration of diffusion tensor images using a viscous fluid model and mutual information.

In this paper, a nonrigid coregistration algorithm based on a viscous fluid model is proposed that has been optimized for diffusion tensor images (DTI), in which image correspondence is measured by the mutual information criterion. Several coregistration strategies are introduced and evaluated both on simulated data and on brain intersubject DTI data. Two tensor reorientation methods have been incorporated and quantitatively evaluated.

Gender differences and age-related white matter changes of the human brain: a diffusion tensor imaging study.

Cerebral white matter undergoes various changes with normal aging. This study investigated the association between age, gender, and the global and regional fractional anisotropy (FA) and mean diffusivity (MD) in 145 adults (30 to 80 years old) using diffusion tensor magnetic resonance imaging. We studied sixteen regions of interest in both hemispheres to search for regions that display age- and gender-related white matter changes and also performed a complementary voxel-based analysis without any hypothesis a priori.

Influence of user-defined parameters on diffusion tensor tractography of the corticospinal tract.

This study discusses the influence of user-defined parameters on fiber tracking results obtained from a standard deterministic streamline tractography algorithm. Diffusion tensor imaging with fiber tractography was performed in five healthy volunteers. A region of interest was highlighted in the ventral part of the pons at the level of the middle cerebellar peduncle.

Multiscale white matter fiber tract coregistration: a new feature-based approach to align diffusion tensor data.

In this paper an automatic multiscale feature-based rigid-body coregistration technique for diffusion tensor imaging (DTI) based on the local curvature kappa and torsion tau of the white matter (WM) fiber pathways is presented. As a similarity measure, the mean squared difference (MSD) of corresponding fiber pathways in (kappa, tau)-space is chosen. After the MSD is minimized along the arc length of the curve, principal component analysis is applied to calculate the transformation parameters.

In vivo diffusion tensor imaging (DTI) of brain subdivisions and vocal pathways in songbirds.

The neural substrate for song behavior in songbirds, the song control system (SCS), is thus far the best-documented brain circuit in which to study neuroplasticity and adult neurogenesis. Not only does the volume of the key song control nuclei change in size, but also the density of the connections between them changes as a function of seasonal and hormonal influences. This study explores the potentials of in vivo Diffusion-Tensor MRI (DT-MRI or DTI) to visualize the distinct, concentrated connections of the SCS in the brain of the starling (Sturnus vulgaris).

Mathematical framework for simulating diffusion tensor MR neural fiber bundles.

White matter (WM) fiber tractography (i.e., the reconstruction of the 3D architecture of WM fiber pathways) is known to be an important application of diffusion tensor magnetic resonance imaging (DT-MRI).

The effects of long-term open-air fumigation with SO on a field crop of broad bean (Vicia faba L.) I. Depression of growth and yield.

In an open-air Held exposure system for the controlled release of air pollutants, broad bean (Vida faba L.) crops were exposed to elevated SO concentrations in three growing seasons, in order to analyse the effects on crop growth under field conditions. The treated plots were exposed to a mean concentration of 165μgm in 1985, 62μgm in 1986 and 74μgm in 1988.

The effects of long-term open-air fumigation with SO on a field crop of broad bean (Vicia faba L.) II Effects on growth components, leaf area development and elemental composition.

Faba bean crops (Vicia faba L.) were exposed to elevated SO concentrations in three different years in an open-air field exposure system for the controlled release of air pollutants. The treated crops were exposed to an average SO, concentration of 165μg m in 1985, 62μg m in 1986 and 74μg m in 1988.