How does water diffusion in human white matter change following ischemic stroke?

Area of Science:

• Neuroimaging
• Diffusion MRI
• Stroke research

Background:

• Ischemic stroke causes white matter damage.
• Water apparent diffusion coefficients (ADC) reflect tissue microstructure.
• Temporal ADC changes in white matter tracts post-stroke are not well understood.

Purpose of the Study:

• To systematically quantify the temporal evolution of ADC parallel and perpendicular to white matter tracts after ischemia.
• To investigate if these ADC changes can be explained by a model of ischemic edema.

Main Methods:

• Retrospective analysis of 53 patients with ischemic lesions in the posterior limb of the internal capsule (PLIC).
• Regions of interest placed on ADC maps to measure ADC parallel and ADC perpendicular.
• Regression analysis of lesion-to-contralateral ADC ratios against time post-stroke, fitted to a biophysical model.

Main Results:

• ADC parallel decreased over time (1-1600 hours post-stroke), with distinct phases.
• ADC perpendicular showed an increasing trend over time, also with distinct phases.
• Model fitting indicated decreasing axonal volume, increasing focal swelling volume, and stable extracellular volume.

Conclusions:

• In human PLIC, ADC parallel decreases and ADC perpendicular increases in the days following stroke.
• This temporal evolution supports the hypothesis of progressive focal cytoplasmic swelling in glial cells and axons.
• Findings are consistent with observations from animal models of ischemic white matter injury.