Diffusion tensor imaging in patients with primary cervical dystonia and in patients with blepharospasm

Diffusion tensor imaging (DTI) analyses the movement of water molecules within the cerebral white matter thus providing information on ultrastructural brain changes. We studied 18 patients with cervical dystonia (CD), 16 with blepharospasm (BSP) and 35 years age-matched healthy controls. DTI data were obtained with a Philips 1.5 Tesla scanner and then processed to obtain maps of fractional anisotropy (FA) and mean diffusivity (MD). Twenty-three square regions of interest of uniform size were positioned on the FA maps and then automatically transferred to the MD maps. FA and MD values in the corpus callosum, left and right putamen, right caudate, left and right pre-frontal cortical area and left supplementary motor area in CD patients differed significantly from those in healthy controls. No significant regional differences were found between patients with BSP and healthy controls. In the CD group, age, duration and severity of dystonia did not correlate with regional FA/MD values, whereas the duration of botulinum toxin treatment correlated significantly with the MD value in the right-pre-frontal cortex. The abnormal DTI findings in patients with CD suggest the presence of brain ultrastructural changes in adult-onset primary CD.     

Diffusion tensor imaging in blepharospasm and blepharospasm-oromandibular dystonia

Patterns of white matter (WM) abnormalities and correlation with clinical features in patients with blepharospasm (BSP) and patients with blepharospasm-oromandibular dystonia (BOM) remain unknown. Using voxel-based analysis, diffusion behaviors of WM including fractional anisotropy (FA), mean diffusivity (MD) and eigenvalues were compared between 20 BSP patients vs. 11 healthy controls (HCs) and 11 patients with BOM vs. 11 HCs. Correlation analyses were performed to assess possible association between diffusion behaviors of significantly different areas and clinical measures. Compared with HCs, BSP patients showed significant FA reductions in the left anterior lobe of cerebellum. Significant increases of MD and radial diffusivity (RD) were detected in right lentiform nucleus and thalamus. Significantly decreased FA in the right precuneus of parietal lobe, increased MD in the right lentiform nucleus and insula, and increased axial diffusivity in the right insula were observed in BOM patients. The FA values in the WM of left cerebellum negatively correlated with disease severity in BSP patients measured by JRS (r = ?0.655, p = 0.002). The FA values in the right parietal WM negatively correlated with disease duration in BOM patients (r = ?0.745, p = 0.008). Both BSP and BOM are related to microstructural abnormalities of WM in the basal ganglia. WM changes outside the basal ganglia may present trait features that are specific for individual dystonia phenotype. The correlation between FA abnormalities and symptom severity suggests that DTI parameters might be of clinical value in assessing and following disability in BSP patients.     

Diffusion tensor imaging of mouse brain stem and cervical spinal cord

In vivo diffusion tensor imaging measurements of the mouse brain stem and cervical spinal cord are presented. Utilizing actively decoupled transmit/receive coils, high resolution diffusion images (117 microm x 59 microm x 500 microm) were acquired at 4.7 T within an hour. Both brain stem and cervical spine displayed clear gray-white matter contrast. The cervical spinal cord white matter showed similar tissue characteristics as seen in the thoracic cord. The coherent fiber orientation in the white matter was observed in both the brain stem and the cervical spinal cord. The results may serve as a reference for future inter-lab comparison in mouse brain stem and cervical spine diffusion measurements.     

Diffusion tensor imaging in brainstem tuberculoma

Integrity of descending white matter tracts can be evaluated by diffusion tensor imaging. In rim-enhancing intraparenchymal lesions, this technique can assist in the differentiation of demyelinating disease from tumor or abscess. Diffusion tensor imaging characteristics of tuberculoma have not been previously reported to our knowledge. A patient with headaches, dizziness, and mild left-sided weakness underwent MRI with diffusion tensor imaging. A large, rim-enhancing lesion within the pons was discovered, which subsequently was diagnosed as tuberculoma. Tractography maps prepared from diffusion tensor imaging data revealed predominantly displaced descending fiber tracts in the region of the rim-enhancing lesion. A few tracts adjacent to the lesion appeared truncated, and this abnormal finding correlated to the patient’s clinical deficit. The tractography characteristics of diffusion tensor imaging in this patient potentially are distinct from those seen with demyelinating lesions, which may show more extensive tract truncation. Together with the consonance of exam findings and tract truncation seen in this patient, tractography may prove useful in the diagnosis of suspected tuberculoma.     

Diffusion tensor imaging in radiosurgical callosotomy

Callosotomy by radioneurosurgery induces slow and progressive axonal degeneration of white matter fibers, a key consequence of neuronal or axonal injury (radionecrosis). However, the acute effects are not apparent when using conventional MRI techniques. Diffusion tensor imaging (DTI) during the first week following radioneurosurgical callosotomy allowed evaluation of these microstructural changes. The present report details that the use of sequential DTI to evaluate axonal degeneration following radioneurosurgical callosotomy in a patient normalized with the data of six healthy subjects. We describe a 25-year old woman with symptomatic generalized epilepsy who underwent a radioneurosurgical callosotomy using LINAC (Novalis^® BrainLAB). DTI was acquired at the baseline, 3 and 9 months and showed a progressive decrease of the fractional anisotropy values in the irradiated areas compared to the controls that could be interpreted as a progressive disconnection of callosal fibers related to the outcome.     

Diffusion tensor imaging in schizophrenia.

Diffusion tensor imaging (DTI) is a magnetic resonance imaging technique that is increasingly being used for the non-invasive evaluation of brain white matter abnormalities. In this review, we discuss the basic principles of DTI, its roots and the contribution of European centres in its development, and we review the findings from DTI studies in schizophrenia. We searched EMBASE, PubMed, PsychInfo, and Medline from February 1998 to December 2006 using as keywords 'schizophrenia', 'diffusion', 'tensor', and 'DTI'. Forty studies fulfilling the inclusion criteria of this review were included and systematically reviewed. White matter abnormalities in many diverse brain regions were identified in schizophrenia. Although the findings are not completely consistent, frontal and temporal white matter seems to be more commonly affected. Limitations and future directions of this method are discussed.     

Diffusion tensor imaging in metachromatic leukodystrophy

Journal of Neurology - We aimed to gain more insight into the pathomechanisms of metachromatic leukodystrophy (MLD), by comparing magnitude and direction of diffusion between patients and controls...     

Diffusion tensor imaging in schizophrenia.

BACKGROUND: Diffusion tensor imaging (DTI) is a relatively new neuroimaging technique that can be used to examine the microstructure of white matter in vivo. A systematic review of DTI studies in schizophrenia was undertaken to test the hypothesis that DTI can detect white matter differences between schizophrenia patients and normal control subjects. METHODS: EMBASE, PubMed, Medline, and PsychInfo were searched online and key journals were searched manually for studies comparing anisotropy (a measure of white matter integrity) between patients and control subjects. Nineteen articles were systematically reviewed. RESULTS: Though 16 studies found differences, methodological and data differences prevented a meta-analysis. Fourteen studies found reduced anisotropy in patients; two studies found only a loss of normal asymmetry. The region of investigation varied across studies, however, and when the same region (for example, the cingulum) was examined in different studies, as many failed to find a difference as found one. These inconsistencies may be the result of small sample sizes and differences in methodology. CONCLUSIONS: Diffusion tensor imaging has yet to provide consistent findings of white matter abnormalities in schizophrenia. Its potential as a means of examining anatomical connectivity may be realized with the study of larger, more homogenous groups of subjects and with ongoing improvements in image analysis.     

Diffusion tensor imaging in schizophrenia.

BACKGROUND: Alignment of white matter axons as inferred from diffusion tensor imaging has indicated changes in schizophrenia in frontal and frontotemporal white matter. METHODS: Diffusion tensor anisotropy and anatomical magnetic resonance images were acquired in 64 patients with schizophrenia and 55 normal volunteers. Anatomical images were acquired with a magnetization prepared rapid gradient echo sequence, and diffusion tensor images used a pulsed gradient spin-echo acquisition. Images were aligned and warped to a standard brain, and anisotropy in normal volunteers and patients was compared using significance probability mapping. RESULTS: Patients showed widespread areas of reduced anisotropy, including the frontal white matter, the corpus callosum, and the frontal longitudinal fasciculus. CONCLUSIONS: These findings, which are consistent with earlier reports of frontal decreases in anisotropy, demonstrate that the effects are most prominent in frontal and callosal areas and are particularly widespread in frontal white matter regions.     

Diffusion tensor imaging and aging

Magnetic resonance diffusion tensor imaging (DTI) is a non-invasive in vivo method for characterizing the integrity of anatomical connections and white matter circuitry and provides a quantitative assessment of the brain's white matter microstructure. DTI studies reveal age-related declines in white matter fractional ansiotropy (FA) in normal healthy adults in whom volume declines are not necessarily detectable. The decline is equivalent in men and women, is linear from about age 20 years onwards, and has a frontal distribution. Studies combining regional DTI metrics and tests of specific cognitive and motor functions have shown that age-related declines in white matter integrity are associated with similar declines in interhemispheric transfer, especially dependent on frontal systems. Emerging from recent DTI findings and conceptualizations of neural causes of cognitive decline in aging, we propose three white matter-mediated neural system hypotheses of aging brain structure and function: (1) the anteroposterior gradient, (2) bilateral recruitment of brain systems via the corpus callosum for frontally based task execution, and (3) frontocerebellar synergism. These hypotheses are not mutually exclusive but establish a basis for posing testable questions about brain systems recruited when those used in youth are altered by aging.     

Diffusion tensor imaging in frontal lobe epilepsy

We report a 13-year-old female with refractory frontal lobe epilepsy in whom diffusion tensor imaging was useful for exploring subtle cortical malformation. She had frequent simple partial seizures characterized by clonic movement of the right upper extremity. Conventional magnetic resonance imaging was not conclusive. A diffusion tensor imaging revealed an increased apparent diffusion coefficient and reduced anisotropy in the left frontal lobe. Positron emission tomography disclosed hypermetabolism in the adjacent area. We could identify the relatively thick cortex with an indistinct gray-white matter junction in a thin-slice T(1)-weighted image.     

Diffusion tensor imaging in early Alzheimer's disease

Our aim was to investigate the extent of white matter tissue damage in patients with early Alzheimer disease (AD) using diffusion tensor magnetic resonance imaging (DTI). Although AD pathology mainly affects cortical grey matter, previous magnetic resonance imaging (MRI) studies showed that changes also exist in the white matter (WM). However, the nature of AD-associated WM damage is still unclear. Conventional and DTI examinations (b=1000 s/mm(2), 25 directions) were obtained from 12 patients with early AD (Mini Mental State Examination [MMSE] score=27, Grober and Buschke test score=33.2, digit span score=5.6) and 12 sex- and age-matched volunteers. The right and left mean diffusivity (MD) and fractional anisotropy (FA) of several WM regions were pooled in each patient and control, and compared between the two groups. Volumes of the whole brain and degree of atrophy of the temporal lobe were compared between the two groups. In AD, MD was increased in the splenium of the corpus callosum and in the WM in the frontal and parietal lobes. FA was bilaterally decreased in the WM of the temporal lobe, the frontal lobe and the splenium compared with corresponding regions in controls. Values in other areas (occipital area, superior temporal area, cingulum, internal capsule, and genu of the corpus callosum) were not different between patients and controls. No correlations were found between the MMSE score and the anisotropy indices. Findings of DTI reveal abnormalities in the frontal and temporal WM in early AD patients. These changes are compatible with early temporal-to-frontal disconnections.     

Diffusion tensor imaging in temporal lobe epilepsy

Although mesial temporal sclerosis (MTS) has long been recognized in association with temporal lobe epilepsy (TLE), there is a growing body of literature suggesting structural abnormalities extending beyond the temporal lobe in patients with TLE. Diffusion tensor imaging (DTI) is a novel imaging technique that provides insight into the structural integrity of cerebral white matter. DTI studies have demonstrated extensive bilateral white matter abnormalities in TLE that extend far beyond the temporal lobe, even in patients with unilateral MTS. The relationship between white matter abnormalities, seizures, and comorbidity in TLE remains unclear.     

Diffusion tensor imaging in late posttraumatic epilepsy

PURPOSE: The main objective of this study was to use diffusion tensor imaging (DTI) to search and quantify the extent of abnormality beyond the obvious lesions seen on the T2 and fluid-attenuation inversion recovery (FLAIR) magnetic resonance images in patients with chronic traumatic brain injury (TBI) with and without epilepsy. METHODS: DTI was performed on 23 chronic TBI patients (with late posttraumatic epilepsy, n=14; without epilepsy, n=9) and 11 age-matched controls. The ratios of fractional anisotropy (FA) and mean diffusivity (MD) between the regions of interest beyond the T2/FLAIR-visualized abnormality and the corresponding contralateral normal-appearing region were calculated. FA and MD ratios were compared for relative changes in these parameters among the TBI subjects with and without epilepsy and controls. Tissue volumes exhibiting abnormalities on DTI also were measured in these patients. RESULTS: The mean regional FA ratio was significantly lower, whereas the mean regional MD value was higher in patients with TBI compared with controls. The mean regional FA ratio was significantly lower in TBI patients with epilepsy (0.57+/-0.059) than in those without epilepsy (0.68+/-0.039). Although the regional MD ratio was higher in TBI patients with epilepsy (1.15+/-0.140) relative to those without epilepsy (1.09+/-0.141), the difference did not reach statistical significance. The tissue volume with low FA value also was found to be higher in TBI patients with epilepsy than without. CONCLUSIONS: Severity of injury as predicted by the DTI-derived increased volume of microstructure damage is associated with delayed posttraumatic epilepsy in TBI patients. These findings could be valuable in predicting epileptogenesis in patients with chronic TBI.     

Diffusion tensor imaging of the brain

Diffusion tensor imaging (DTI) is a promising method for characterizing microstructural changes or differences with neuropathology and treatment. The diffusion tensor may be used to characterize the magnitude, the degree of anisotropy, and the orientation of directional diffusion. This review addresses the biological mechanisms, acquisition, and analysis of DTI measurements. The relationships between DTI measures and white matter pathologic features (e.g., ischemia, myelination, axonal damage, inflammation, and edema) are summarized. Applications of DTI to tissue characterization in neurotherapeutic applications are reviewed. The interpretations of common DTI measures (mean diffusivity, MD; fractional anisotropy, FA; radial diffusivity, D _r; and axial diffusivity, D _a) are discussed. In particular, FA is highly sensitive to microstructural changes, but not very specific to the type of changes (e.g., radial or axial). To maximize the specificity and better characterize the tissue microstructure, future studies should use multiple diffusion tensor measures (e.g., MD and FA, or D _a and D _r).     

Diffusion tensor magnetic resonance imaging.

Molecular diffusion plays an important role in many biologic phenomena. The ability to study diffusion, therefore, is extremely useful in physiology and medicine. MRI offers a non-invasive window to diffusion, particularly water self-diffusion. MRI techniques, which provide diffusion sensitivity or quantitation (diffusion tensor MRI [DTI]), have found widespread application in neuroscience and medicine, including the evaluation of stroke, brain development, tumor imaging, and demyelinating disorders. We discuss the tensor nature of diffusion and provide an overview of how DTI offers unique information on tissue organization, water mobility, and disease states, particularly those of neuro-ophthalmologic interest.     

Diffusion tensor brain imaging and tractography

Diffusion-tensor MR imaging is a promising tool to evaluate white-matter integrity by quantitative and graphic maps including neural fiber tractogram. Current challenges afoot are to obtain higher quality diffusion-weighted MR images (high SNR, isotropic voxel, and high spatial resolution), to create a robust mathematical framework to process the data, to construct a user-friendly computer-based algorithm, to reveal determinants of diffusion process, and to establish analytical methodology.     

Diffusion tensor imaging of cocaine-treated rodents

Studies in cocaine-dependent human subjects have shown differences in white matter on diffusion tensor imaging (DTI) compared with non-drug-using controls. It is not known whether the differences in fractional anisotropy (FA) seen on DTI in white matter regions of cocaine-dependent humans result from a pre-existing predilection for drug use or purely from cocaine abuse. To study the effect of cocaine on brain white matter, DTI was performed on 24 rats after continuous infusion of cocaine or saline for 4 weeks, followed by brain histology. Voxel-based morphometry analysis showed an 18% FA decrease in the splenium of the corpus callosum (CC) in cocaine-treated animals relative to saline controls. On histology, significant increase in neurofilament expression (125%) and decrease in myelin basic protein (40%) were observed in the same region in cocaine-treated animals. This study supports the hypothesis that chronic cocaine use alters white matter integrity in human CC. Unlike humans, where the FA in the genu differed between cocaine users and non-users, the splenium was affected in rats. These differences between rodent and human findings could be due to several factors that include differences in the brain structure and function between species and/or the dose, timing, and duration of cocaine administration.     

Diffusion tensor imaging of subependymal heterotopia

A magnetic resonance (MR) diffusion tensor imaging (DTI) study was performed in a newborn with bilateral subependymal heterotopia (SE). White matter fractional anisotropy (FA), axial diffusivity (AD) and radial diffusivity (RD) were compared to values obtained in four newborns with moderate perinatal asphyxia and normal MRI findings. The reduction of FA and increase of AD and RD in the newborn with SE were the in vivo late expression of alterations in the intermediate zone, with an underlying arrest of neuronal migration.