Regional cerebral blood volume response to hypocapnia using susceptibilitycontrast MRI

We used steady-state susceptibility contrast MRT to evaluate the regional c erebral blood volume (rCBV) response to hypocapnia in anesthetised rats. Th e rCBV was determined in the dorsoparietal neocortex, the corpus striatum, the cerebellum, as well as blood volume in extracerebral tissue (group 1). In addition, we used laser-Doppler flow (LDF) measurements in the left dors oparietal neocortex (group 2), to correlate changes in CBV and in cerebral blood how. Baseline values, expressed as a percentage of blood volume in ea ch voxel, were higher in the brain regions than in extracerebral tissue. Hy pocapnia (PaCO2 approximate to 25 mmHg) resulted in a significant decrease in CBV in the cerebellum (-17 +/- 9%), in the corpus striatum (-15 +/- 6%) and in the neocortex (-12 +/- 7%), compared to the normocapnic CBV values ( group 1). These changes were in good agreement with the values obtained usi ng alternative techniques. No significant changes in blood volume were foun d in extracerebral tissue. The CBV changes were reversed during the recover y period. In the left dorsoparietal neocortex, the reduction in LDF (group 2) induced by hypocapnia (-21 +/- 8%) was in accordance with the values pre dicted by the Poiseuille's law. We conclude that rCBV changes during CO2 ma nipulation can be accurately measured by susceptibility contrast MRI. Copyr ight (C) 2000 John Wiley & Sons, Ltd.