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Diffusion-weighted MR imaging of the hippocampus and temporal white matter in Alzheimer's disease
Abstract:
We investigated the changes in water diffusion in the hippocampus and the temporal white matter (the temporal stem) in eight patients with possible Alzheimer's disease (AD), 10 patients with probable AD, and 10 age-matched controls, using coronal diffusion-weighted magnetic resonance (MR) imaging. Apparent diffusion coefficients (ADCs) were derived for the three orthogonal axes and an index of diffusion anisotropy (IDA = ADC(max-min)/ADC(mean)) was then calculated. Although no significant differences were found in ADC and IDA values in the hippocampal body between controls and patients, vertical (superior-inferior) ADC values and ADC(mean) values in the temporal stem of patients with AD were significantly higher than those in controls, and IDA values were therefore significantly lower in patients with possible or probable AD than those in controls. Moreover, IDA values in the temporal stem were significantly correlated with the clinical severity. These results suggest that decreased fiber density, such as the disruption and loss of axonal membranes or myelin, occur early in the temporal stem, probably due to secondary degeneration related to grey matter pathology including the medial temporal lobe.
Insights
Alzheimer's disease (AD) is linked to altered water diffusion in the brain's temporal stem. Diffusion changes in the temporal stem correlate with AD severity, suggesting early fiber degeneration.
Area of Science:
- Neuroimaging
- Neurology
- Biomedical Engineering
Background:
- Alzheimer's disease (AD) is a progressive neurodegenerative disorder.
- Early detection of AD pathology is crucial for timely intervention.
- Water diffusion Magnetic Resonance (MR) imaging offers insights into brain tissue microstructure.
Purpose of the Study:
- To investigate alterations in water diffusion within the hippocampus and temporal stem in patients with possible or probable Alzheimer's disease (AD).
- To correlate diffusion parameters with the clinical severity of AD.
Main Methods:
- Coronal diffusion-weighted MR imaging was employed.
- Apparent diffusion coefficients (ADCs) and an index of diffusion anisotropy (IDA) were calculated for the hippocampus and temporal stem.
- Data from patients with possible AD, probable AD, and age-matched controls were analyzed.
Main Results:
- No significant differences in ADC or IDA were observed in the hippocampal body.
- Significantly higher vertical ADC and ADC(mean) values were found in the temporal stem of AD patients compared to controls.
- Significantly lower IDA values were observed in the temporal stem of AD patients, correlating with clinical severity.
Conclusions:
- Water diffusion changes, specifically increased ADC and decreased IDA, in the temporal stem are indicative of early neurodegeneration in AD.
- These findings suggest early disruption of fiber density in the temporal stem, likely due to secondary degeneration related to medial temporal lobe pathology.