Dynamic changes in cerebral blood flow and angiogenesis after transient focal cerebral ischemia in rats. Evaluation with serial magnetic resonance imaging.

Background and Purpose: Angiogenesis occurs after cerebral ischemia, but the relationship between angiogenesis and cerebral hemodynamic change is unknown. The aim of the present study was to investigate the relationship between ischemia-induced angiogenesis and hemodynamics in a well-defined 3-vessel occlusion model of the rat by using diffusion- (DWI), perfusion-, and T2-weighted MRI (T2WI).
Methods: Rats were subjected to 60 minutes of transient middle cerebral artery occlusion or sham operation. DWI and T2WI were used to characterize the extent of the ischemic lesion from 4.5 hours to 14 days after reperfusion. A flow-sensitive alternating inversion recovery method and dynamic susceptibility contrast MRI were used to evaluate the temporal changes in relative cerebral blood flow (CBF) and cerebral blood volume (CBV), respectively. Rats were randomly selected and killed at each time point for investigation of vascular density and for hematoxylin-eosin staining.
Results: Ischemic lesions developed in the ipsilateral cortex, as demonstrated by DWI and T2WI. CBF was significantly increased in the ipsilateral cortex, especially in the cortical outer layer from day 1 to day 14, and peaked on day 7 (P<0.05), while CBV was significantly increased on day 7 (P<0.01). The vascular density on the ipsilateral brain surface was gradually increased from day 1 to day 5, peaked on day 7, and then decreased on day 14. Histology study showed pannecrosis in the cortex from day 1 to day 5 and partial liquefaction of the necrotic tissues on days 7 and 14.
Conclusions: A delayed increase in both CBF and CBV is documented in the ipsilateral cortex after transient focal brain ischemia, and such an increase may be associated with angiogenesis.