الفهرس 
Anatomy of Brain White Matter TractsOnly 14 pages are availabe for public view
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Abstract
Alzheimer disease (AD) is the most common cause of dementia in the elderly. The disease usually becomes clinically apparent as insidious impairment of higher intellectual function, with alterations in mood and behavior. Later, progressive disorientation, memory loss, and aphasia become manifest, indicating severe cortical dysfunction.
While pathologic examination of brain tissue remains necessary for the definitive diagnosis of Alzheimer disease, the combination of clinical assessment and modern radiologic methods allows accurate diagnosis in 80% to 90% of cases of AD.
AD is characterized by cortical brain atrophy, mainly involving the temporal and parietal regions with disproportionate hippocampal volume loss. This brain atrophy may be assessed in vivo using conventional CT and MRI volumetry. However, neuroanatomical changes over time may be too mild, diffuse, or topographically complex to be detected by simple visual inspection or even with manually traced measurements of regions of interest.
Recent evidence suggests that an understanding of brain aging and the aging-related processes of myelin production and subsequent breakdown may be relevant to creating a useful conceptual model aimed at understanding aging, AD, and possibly other age-related neurodegenerative disorders. This model suggests that because of the unique vulnerability of late-developing oligodendrocytes, myelin breakdown is at the core of the earliest changes involved in both brain aging and AD.
DTI is an MRI scanning technique that allows for the examination of white matter microstructural integrity based on the directionality of diffusion in the brain. DTI indices of cerebral damage are commonly found in AD. The majority of DTI changes appear to be in more posterior regions compared to frontal regional changes that are more common in healthy aging. The most commonly reported regions of DTI alterations are the temporal lobes, with particular emphasis on the parahippocampal white matter, and the posterior cingulum. Both of these regions are strongly implicated in memory function.
It is important to note that there are many conflicting reports on regional disruption of DTI measures in AD compared to healthy controls. Indeed, there are a few studies that do not find any significant differences in DTI measures between memory-impaired subjects and controls. The reasons for these conflicting reports are not clear.
Techniques such as tract-based analysis of white matter pathways and individually traced ROIs, along with advances in DTI pulse sequences, hold promise for providing additional information on the status of white matter in AD.
Conclusion:
While not without drawbacks, DTI is proving to be a very valuable neuroradiological tool for the early diagnosis of AD through detecting the integrity of white matter tracts involved in the early stages of the disease process.