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Temporal evolution of water diffusion parameters is different in grey and white matter in human ischaemic stroke

¹ Medical and Radiological Sciences (Medical Physics), University of Edinburgh, Edinburgh, UK
² Clinical Neurosciences, University of Edinburgh, Edinburgh, UK

Correspondence to:
Correspondence to:
Dr M Bastin
Medical and Radiological Sciences (Medical Physics), University of Edinburgh, Western General Hospital, Crewe Road, Edinburgh, EH4 2XU; meb{at}skull.dcn.ed.ac.uk

Objectives: Our purpose was to investigate whether differences exist in the values and temporal evolution of mean diffusivity (<D>) and fractional anisotropy (FA) of grey and white matter after human ischaemic stroke.

Methods: Thirty two patients with lesions affecting both grey and white matter underwent serial diffusion tensor magnetic resonance imaging (DT-MRI) within 24 hours, and at 4–7 days, 10–14 days, 1 month, and 3 months after stroke. Multiple small circular regions of interest (ROI) were placed in the grey and white matter within the lesion and in the contralateral hemisphere. Values of <D>{grey}, <D>{white}, FA{grey} and FA{white} were measured in these ROI at each time point and the ratios of ischaemic to normal contralateral values (<D>_R and FA_R) calculated.

Results: <D> and FA showed different patterns of evolution after stroke. After an initial decline, the rate of increase of <D>{grey} was faster than <D>{white} from 4–7 to 10–14 days. FA{white} decreased more rapidly than FA{grey} during the first week, thereafter for both tissue types the FA decreased gradually. However, FA{white} was still higher than FA{grey} at three months indicating that some organised axonal structure remained. This effect was more marked in some patients than in others. <D>_R{grey} was significantly higher than <D>_R{white} within 24 hours and at 10–14 days (p<0.05), and FA_R{white} was significantly more reduced than FA_R{grey} at all time points (p<0.001).

Conclusions: The values and temporal evolution of <D> and FA are different for grey and white matter after human ischaemic stroke. The observation that there is patient-to-patient variability in the degree of white matter structure remaining within the infarct at three months may have implications for predicting patient outcome.

Abbreviations: ADC, apparent diffusion coefficient; CT, computed tomography; <D>, mean diffusivity; DT-MRI, diffusion tensor magnetic resonance imaging; DW-MRI, diffusion-weighted MRI; EP, echo planar; FA, fractional anisotropy; ROI, regions of interest

Keywords: ischaemic stroke; grey and white matter; magnetic resonance imaging; diffusion tensor

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