Diffusion-weighted arterial spin labeling MRI to investigate mannitol-induced blood brain barrier disruption.

PURPOSE: Diffusion-weighted arterial spin labeling (DW-ASL) MRI has been proposed to determine the rate of water exchange (Kw) across the blood brain barrier (BBB). This study aims to further evaluate Kw MRI by comparing it with standard dynamic contrast-enhanced (DCE) MRI and histology in association with mannitol-induced disruption of the BBB.

METHODS

DW-ASL was measured using a multiple b-value MRI protocol in normal rats at three post-labeling delays (N = 19), before and after intra-carotid injection of mannitol to disrupt BBB in one hemisphere (N = 13). An approach using only two b-values to detect mannitol-induced changes was also tested. DCE MRI and Evans blue histology were performed on the same animals. Quantitative analysis and pixel-by-pixel correlation were performed amongst Kw, DCE MRI and Evans blue histology.

RESULTS

Kw in the grey matter in the normal rat brain was 252 ± 38 min-1 (±standard error of the mean). The two b-value approach provided reasonable approximation of multiple-b DW-ASL parameters, reducing acquisition time. Kw is sensitive to mannitol-induced changes in BBB permeability and was reduced to 89 ± 17 min-1 in the affected hemisphere compared to 191 ± 22 min-1 in the unaffected hemisphere (P < 0.05). Regions with abnormality in Kw maps were in general agreement with DCE and Evans blue maps, although there are some distinct differences in location and the change in values.

CONCLUSION

Kw is sensitive to mannitol-induced changes in the BBB, with BBB disruption confirmed by DCE MRI and Evans blue histology.