Biomedical Imaging Technology Center
Diffusion tensor imaging (DTI) is a powerful technique that provides quantitative information about the microscopic integrity of white matter. Diffusion in biological tissues can be restricted or anisotropic (i.e. orientation dependent) due to tissue structure. Some tissues, such as white matter tracts, possess a higher degree of diffusion anisotropy than others, such as gray matter. Loss of tissue structure results in an increase in the diffusion coefficient and a reduction in anisotropy. DTI can generate maps of diffusion coefficient and diffusion anisotropy, as well as neural fiber tracts. It is thus a unique method for studying the development of white matter structure and therefore connectivity, and assessing the severity of tract disruption in disease states. For example, by identifying specific axonal pathways in the brain and determining the degree of disruption, DTI in patients with Alzheimer's disease should allow to test neuropsychological hypotheses regarding the specific pathways disrupted.
Our study are currently focusing on investigating the use of diffusion tensor imaging in studying white matter changes in the brains of patients with fetal alcohol syndrome (FAS), Alzheimer's disease (AD), Parkinson.s disease (PD), and normal aging in a high field (3T) MRI scanner.
Figure 1: DTI results from a FAS patient. From left to right: T2, ADC, FA, and Color maps. DTI images acquired with 12 directions at b=1000 mm2/s. ROI measurements in the genu and the splenium of the corpus callosum (CCg and CCs) in FAS patients showed a lower FA value and a higher ADC value compared to those in normal volunteers. Since brain regions with dense and highly orientated fiber bundles have a high anisotropy, the decrease in FA in FAS patients suggest that there is abnormal development of white matter in CC causing degradation of the corpus callosum, such that fibers are less dense or less organized and the diffusion becomes more isotropic. Also, the results from these subjects suggest that changes in FA may be proportionally related with physical dysmorphia since patients with more dysmorphia were found to have larger changes in FA and ADC values. This study indicates that anisotropy measurement with DTI can be very sensitive in examining the neurodevelopmental effects of teratogens.
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