Diffusion Tensor MRI Measurements Research Articles

Diffusion tensor MRI to assess skeletal muscle disruption following eccentric exercise

Structural evidence of exercise-induced muscle disruption has traditionally involved histological analysis of muscle tissue obtained by needle biopsy, however, there are multiple limitations with this technique. Recently, diffusion tensor magnetic resonance imaging (DT-MRI) has been successfully demonstrated to noninvasively assess skeletal muscle abnormalities induced by traumatic injury. To determine the potential for DT-MRI to detect musculoskeletal changes after a bout of eccentric exercise, 10 healthy men performed 300 eccentric actions on an isokinetic dynamometer. DT-MRI measurements and muscle biopsies from the vastus lateralis were obtained before and 24 h post-exercise. Z-band streaming was higher 24 h post-exercise compared with baseline (P < 0.05). The histological indices of damage coincided with changes in DT-MRI parameters of fractional anisotropy (FA) and apparent diffusion coefficient; reflecting altered skeletal muscle geometry (P < 0.05). Z-band streaming quantified per fiber correlated with FA (r = -0.512; P < 0.05). DT-MRI can detect changes in human skeletal muscle structure following eccentric exercise.

Diffusion tensor MRI contributes to differentiate Richardson's syndrome from PSP-parkinsonism

This study investigated the regional distribution of white matter (WM) damage in Richardson's syndrome (PSP-RS) and progressive supranuclear palsy-Parkinsonism (PSP-P) using diffusion tensor (DT) magnetic resonance imaging (MRI). The DT MRI classificatory ability in diagnosing progressive supranuclear palsy (PSP) syndromes, when used in combination with infratentorial volumetry, was also quantified. In 37 PSP (21 PSP-RS, 16 PSP-P) and 42 controls, the program Tract-Based Spatial Statistics (TBSS; www.fmrib.ox.ac.uk/fsl/tbss) was applied. DT MRI metrics were derived from supratentorial, thalamic, and infratentorial tracts. The magnetic resonance parkinsonism index (MRPI) was calculated. All PSP harbored diffusivity abnormalities in the corpus callosum, frontoparietal, and frontotemporo-occipital tracts. Infratentorial WM and thalamic radiations were severely affected in PSP-RS and relatively spared in PSP-P. When MRPI and DT MRI measures were combined, the discriminatory power increased for each comparison. Distinct patterns of WM alterations occur in PSP-RS and PSP-P. Adding DT MRI measures to MRPI improves the diagnostic accuracy in differentiating each PSP syndrome from healthy individuals and each other.

Focal structural changes and cognitive dysfunction in juvenile myoclonic epilepsy

The aim of this study was to determine if there were focal cortical abnormalities in juvenile myoclonic epilepsy (JME) using neuropsychological investigations and MRI. Twenty-eight patients with JME and a large sample of healthy controls were assessed using a series of neuropsychological tests as well as structural and diffusion tensor MRI (DTI). DTI measures assessed fractional anisotropy (FA) within a white matter skeleton. Neuropsychological testing indicated subtle dysfunctions in verbal fluency, comprehension, and expression, as well as nonverbal memory and mental flexibility. Utilizing whole-brain voxel-based morphometry for gray matter MRI data and tract-based spatial statistics for white matter diffusion MRI data, we found reductions in gray matter volume (GMV) in the supplementary motor area and posterior cingulate cortex and reductions in FA in underlying white matter of the corpus callosum. Supplementary motor area FA predicted scores in word naming tasks and expression scores. Posterior cingulate cortex GMV and FA predicted cognitive inhibition scores on the mental flexibility task. The neuropsychological, structural, and tractography results implicate mesial frontal cortex, especially the supplementary motor area, and posterior cingulate cortex in JME.

Correlation of cognitive dysfunction and diffusion tensor MRI measures in patients with mild and moderate multiple sclerosis

To compare the diffusion tensor imaging (DTI) measures of multiple sclerosis (MS) patients and healthy subjects in every brain voxel and to correlate them with Paced Auditory Serial Addition Test (PASAT) scores. Fractional anisotropy (FA), and mean, longitudinal, and transverse diffusivity are compared between control subjects and MS patients, which were subdivided as mildly and moderately impaired. In addition, PASAT scores are correlated for both MS groups with the diffusion measures. An optimized voxel based analysis (VBA) method, in terms of coregistration, atlas construction, and image smoothing, was thereby used. Diffusion differences between the control subjects and the patients with MS were found in the corpus callosum, inferior longitudinal fasciculus, cortico spinal tracts, forceps major, superior longitudinal fasciculus, and cingulum. In addition, we observed significant correlations of the FA and PASAT scores in the left inferior longitudinal fasciculus, the forceps minor, the capsula interna and externa, the genu of the corpus callosum, the left cingulum, the superior longitudinal fasciculus, and the corona radiata. Diffusion differences were observed between the mildly impaired MS patients and control subjects. In addition, different diffusion measures correlated with PASAT scores for cognitive decline in parietal, frontal, as well as temporal white matter (WM) regions.

In vivo diffusion tensor magnetic resonance imaging and fiber tracking of the mouse brain

Until very recently, the study of neural architecture using fixed tissue has been a major scientific focus of neurologists and neuroanatomists. A non-invasive detailed insight into the brain's axonal connectivity in vivo has only become possible since the development of diffusion tensor magnetic resonance imaging (DT-MRI). This unique approach of analyzing axonal projections in the living brain was used in the present study to describe major white matter fiber tracts of the mouse brain and also to identify for the first time non-invasively the rich connectivity between the amygdala and different target regions. To overcome the difficulties associated with high spatially and temporally resolved DT-MRI measurements a 4-shot diffusion weighted spin echo (SE) echo planar imaging (EPI) protocol was adapted to mouse brain imaging at 9.4T. Diffusion tensor was calculated from data sets acquired by using 30 diffusion gradient directions while keeping the acquisition time at 91 min. Two fiber tracking algorithms were employed. A deterministic approach (fiber assignment by continuous tracking - FACT algorithm) allowed us to identify and generate the 3D representations of various neural pathways. A probabilistic approach was further used for the generation of probability maps of connectivity with which it was possible to investigate - in a statistical sense - all possible connecting pathways between selected seed points. We show here applications to determine the connection probability between regions belonging to the visual or limbic systems. This method does not require a priori knowledge about the projections' trajectories and is shown to be efficient even if the investigated pathway is long or three-dimensionally complex. Additionally, high resolution images of rotational invariant parameters of the diffusion tensor, such as fractional anisotropy, volume ratio or main eigenvalues allowed quantitative comparisons in-between regions of interest (ROIs) and showed significant differences between various white matter regions.

Microstructural abnormalities of striatum and thalamus in children with Tourette syndrome

We applied diffusion-tensor MRI (DT-MRI) to investigate directly the water diffusivity within subcortical gray matter structures comprising the fronto-striato-thalamic (FST) circuit, which is implicated in the pathophysiology of Tourette syndrome (TS). We investigated the structural integrity of basal ganglia and thalamus in 23 children with TS and 35 age-matched healthy controls (NC), and examined the association of DT-MRI measures to tic severity and comorbid symptoms. We measured parallel (lambda(1)) and perpendicular (lambda(23)) diffusivity, mean diffusivity (MD), and fractional anisotropy (FA) in both hemispheres. Compared with NC, the TS group showed a significant increase in lambda(1) (P = 0.003) and MD (P = 0.027) in the bilateral putamen, an increase in lambda(23) in right thalamus (P = 0.008), and a reversed asymmetry of FA (P = 0.03) in the thalamus. There was a significant positive correlation between lambda(23) in right thalamus and tic severity. TS patients showed significantly lower left caudate volume (P = 0.011) and bilateral thalamic volumes (left, P = 0.035, right P = 0.006) compared with NC. These findings support the notion that microstructural dysfunction measured by DT-MRI in component regions of the FST circuit contribute to the pathophysiology in TS.

Regularization of DT-MR images using a successive Fermat median filtering method

Tractography using diffusion tensor magnetic resonance imaging (DT-MRI) is a method to determine the architecture of axonal fibers in the central nervous system by computing the direction of greatest diffusion in the white matter of the brain. To reduce the noise in DT-MRI measurements, a tensor-valued median filter, which is reported to be denoising and structure preserving in the tractography, is applied. In this paper, we proposed the successive Fermat (SF) method, successively using Fermat point theory for a triangle contained in the two-dimensional plane, as a median filtering method. We discussed the error analysis and numerical study about the SF method for phantom and experimental data. By considering the computing time and the image quality aspects of the numerical study simultaneously, we showed that the SF method is much more efficient than the simple median (SM) and gradient descents (GD) methods.

Diffusion anisotropy indexes are sensitive to selecting the EPI readout-encoding bandwidth at high-field MRI

Diffusion tensor magnetic resonance imaging (DT-MRI) is generally performed using an echo planar imaging (EPI) acquisition to map directional water diffusion. However, the oscillating magnetic field gradients of the EPI acquisition can result in considerable mechanical vibrations, which lead, in turn, to magnetic field fluctuations causing Nyquist ghosting in the EPI data. The objective of this study was to investigate effects of EPI readout gradient modulation frequency, which is directly associated with the EPI readout bandwidth (BW), on the accuracy of DT-MRI measurements in a high magnetic field system. A spherical water phantom was used to study the relationship between the EPI BW and the Nyquist ghost for a spin-echo EPI acquisition with a matrix size of 128x128, complemented by diffusion sensitization gradients of up to b=800 s/mm(2) along six directions for DT-MRI. Nine volunteers (four males and five females) were studied using EPI at different BW acquisitions. Analysis of variance was used to investigate the EPI BW effects. The phantom studies demonstrated a systematic relationship between BWs and the intensities of Nyquist ghosts. In the human brain studies, EPI BW variations substantially corrupted diffusion anisotropy indexes (i.e., fractional anisotropy and relative anisotropy) (F=10.5, P=.0001) but were unrelated to diffusion-encoding directions (F=0.14, P=.98). It was possible to minimize BW dependence (F=1.48, P=.25) by tuning the modulation frequency of the EPI readout gradient. In conclusion, diffusion anisotropic indexes are sensitive to the readout BW of EPI due to associated Nyquist ghosting. However, the effect can be minimized by tuning the modulation frequency of the EPI readout gradient, that is, the EPI BW, to a range outside the harmonics of mechanical gradient vibrations.

Normal-appearing white and grey matter damage in MS

The aims of this study were to improve, using a 3.0 Tesla (T) scanner and diffusion tensor (DT) magnetic resonance imaging (MRI) with sensitivity encoding, our understanding of: 1) the possible pathological substrates of normal-appearing white matter (NAWM) and grey matter (GM) damage in multiple sclerosis (MS) and 2) the factors associated to WM and GM atrophy in this condition. Conventional and DT MRI of the brain were acquired from 32 relapsing-remitting (RR) MS patients and 16 controls. Lesion load, WM (WMV), overall GM (GMV), and neocortical GM (NCV) volumes were measured. NAWM mean diffusivity (MD) and fractional anisotropy (FA), and GM MD were calculated. GMV and NCV were lower (p < or = 0.001) in MS patients than controls, whereas WMV did not differ significantly. MS patients had higher NAWM and GM average MD and lower NAWM average FA (p < or = 0.001) than controls. Moderate correlations were found between intrinsic lesion and tissue damage with both GM volumetric and diffusivity changes (-0.41 < or = r < or = 0.42, p < or = 0.04). DT MRI and volumetry measurements at 3.0 T confirm the presence of NAWM and GM abnormalities in RRMS patients. Although histopathology was not available, axonal and neuronal damage and consequent reactive glial proliferation are the most likely substrates of the changes observed.

Diffusion tensor imaging in presymptomatic and early Huntington's disease: Selective white matter pathology and its relationship to clinical measures

Atrophy of cortical and subcortical gray matter is apparent in Huntington's disease (HD) before symptoms manifest. We hypothesized that the white matter (WM) connecting cortical and subcortical regions must also be affected early and that select clinical symptoms were related to systems degeneration. We used diffusion tensor magnetic resonance imaging (DTI) to examine the regional nature of WM abnormalities in early HD, including the preclinical period, and to determine whether regional changes correlated with clinical features. We studied individuals in early stages (HD), presymptomatic individuals known to carry the genetic mutation that causes HD (Pre-HD), and matched healthy controls. DTI indices of tissue integrity were obtained from several regions of interest, including the corpus callosum (CC), internal capsule (IC), and basal ganglia, were compared across groups by t tests, and were correlated to cognitive and clinical measures. WM alterations were found throughout the CC, in the anterior and posterior limbs of the IC, and in frontal subcortical WM in HD subjects, supporting the selective involvement of the pyramidal tracts in HD; a similar distribution of changes was seen in Pre-HD subjects, supporting presymptomatic alterations. There was a significant relationship between select DTI measures and cognitive performance. Alterations in diffusion indices were also seen in the striatum that were independent of atrophy. Our findings support that WM alterations occur very early in HD. The distribution of the changes suggests that these changes contribute to the disruption of pyramidal and extrapyramidal circuits and also support a role of compromised cortical circuitry in early cognitive and subtle motor impairment during the preclinical stages of HD.

Optic nerve diffusion tensor imaging in optic neuritis

Diffusion tensor magnetic resonance imaging (DT-MRI) provides in vivo information about the pathology of multiple sclerosis lesions. Increases in mean diffusivity (MD) and reductions in fractional anisotropy (FA) have been found and may represent axonal disruption. The optic nerve is an ideal structure for study by DT-MRI but previous clinical studies did not obtain the full diffusion tensor necessary to calculate MD and FA. In this study, a technique that was specifically developed to achieve full diffusion tensor measurements from the optic nerve (zonal oblique multislice (ZOOM) echoplanar imaging) was applied to 25 patients with a single unilateral episode of optic neuritis at least one year previously, and 15 controls. The intraorbital nerves were segmented on non-diffusion-weighted images and the regions of interest transferred to MD, FA, and eigenvalue maps to obtain quantitative data. Quantitative visual testing and electrophysiology were also performed. In affected nerves, mean MD and mean orthogonal eigenvalue λ ⊥ were elevated, and mean FA reduced compared with clinically unaffected contralateral nerves ( P < 0.001) and control nerves ( P < 0.001). The mean principal eigenvalue λ \\\\ was significantly increased in affected nerves compared to contralateral unaffected nerves ( P = 0.04) but not compared to control nerves ( P = 0.13). There was no association of clinical measures of visual function in affected eyes with the DT-MRI parameters but there was a significant correlation of the whole field visual evoked potential (VEP) amplitude with MD ( r = −0.57, P = 0.006) and λ ⊥ ( r = −0.56, P = 0.007). These findings suggest that optic nerve DT-MRI measures provide an indication of the structural integrity of axons.

Diffusion Tensor Magnetic Resonance Imaging in Multiple Sclerosis

Multiple sclerosis (MS), a demyelinating disease, occurs principally in the white matter (WM) of the central nervous system. Conventional magnetic resonance imaging (MRI) is sensitive to some, but not all, brain changes associated with MS. Diffusion-weighted imaging (DWI) provides information about water diffusion in tissue and diffusion tensor MRI (DT-MRI) about fiber direction, allowing for the identification of WM abnormalities that are not apparent on conventional MRI images. These techniques can quantitatively characterize the local microstructure of tissues. MS-associated disease processes lead to regions characterized by an increased amount of water diffusion and a decrease in the anisotropy of diffusion direction. These changes have been found to produce different patterns in MS patients presenting different courses of the disease. Changes in water diffusion may allow examination of the type, appearance, enhancement, and location of lesions not readily visible by other means. Ongoing studies of MS are integrating conventional MRI and DT-MRI measures with connectivity-based regional assessment, aiming to provide a better understanding of the nature and the location of WM lesions. This integration and the development of novel image-processing and visualization techniques may improve the understanding of WM architecture and its disruption in MS. This article presents a brief history of DWI, its basic principles and applications in the study of MS, a review of the properties and applications of DT-MRI, and their use in the study of MS. In addition, this article illustrates the methodology for the analysis of DT-MRI in ongoing studies of MS.

A method for obtaining tract-specific diffusion tensor MRI measurements in the presence of disease: application to patients with clinically isolated syndromes suggestive of multiple sclerosis

The aim of this study was to investigate whether neurological symptoms related to a specific axonal fiber tract in brain white matter were associated with a higher degree of tissue damage in that region, in patients at presentation with clinically isolated syndromes (CIS) suggestive of multiple sclerosis. To this end, a magnetic resonance imaging (MRI) method to segment and evaluate the fiber bundle of interest was implemented, taking care to circumvent the problems caused by pathology. Diffusion tensor (DT) MRI tractography was used to construct, from healthy volunteer data, a probability map for the pyramidal tract (PYT), and this map was applied to patients to calculate DT-derived metrics inside the PYT. In CIS patients with clinical symptoms related to motor function, the DT-derived mean diffusivity and the lesion volume in the PYT were found to be increased, while the fractional anisotropy was no different, when compared to those patients without motor symptoms. These results may be explained by several microstructural changes in the damaged tissue, such as changes in the permeability of axonal cell membranes, decreases of axonal density and edema. The approach taken to analyze a specific fiber tract was possible because the axons in the tract have a high orientational coherence, allowing tissue structure changes to be isolated from the tissue architecture. Its extension to other white matter fiber bundles is therefore limited to bundles with high orientational coherence.

Diffusion tensor MRI correlates with executive dysfunction in patients with ischaemic leukoaraiosis

Background: Cerebral small vessel disease is a common cause of vascular dementia. Both discrete lacunar infarcts and more diffuse ischaemic changes, seen as confluent high signal (leukoaraiosis) on T2 weighted...

Computation of the fractional anisotropy and mean diffusivity maps without tensor decoding and diagonalization: Theoretical analysis and validation.

Diffusion tensor MRI (DT-MRI) is a promising modality for in vivo mapping of the organization of deep tissues. The most commonly used DT-MRI invariant maps are the mean diffusivity, mu(D), relative anisotropy (RA), and fractional anisotropy (FA). Because of the computational burden, anisotropy maps are generally computed offline. The availability of a simple procedure to compute RA, FA, and mu(D) online would make DT-MRI more useful in clinical applications that require immediate feedback. In this study, analytical expressions that relate the commonly used tensor anisotropy measures obtained from the decoded and diagonalized DT with those obtained from the first and second moments of the measured diffusion-weighted (DW) data are derived. Specifically, it is shown that for the principal icosahedron encoding scheme, RA is related to the mean and standard deviation (SD) of the DW measurements that can be computed online. Since FA is commonly used as an anisotropy measure, an analytical expression relating RA and FA was derived from the tensor invariants. These results were validated using both Monte Carlo simulations and high-resolution, normal whole-brain DT-MRI measurements acquired with different b-factors, encoding schemes, and signal-to-noise ratio (SNR) levels. The bias introduced by the rotationally variant encoding schemes into the diffusion measures is also investigated.