DYNAMIC FUNCTIONAL IMAGING OF RELATIVE CEREBRAL BLOOD-VOLUME DURING RAT FOREPAW STIMULATION

Dynamic measurements of regional changes in cerebral blood volume (CBV ) were performed in rat models of hypercarbia and focal neuronal activ ation using T-2-weighted imaging after injection of an intravascular c ontrast agent with a very long blood half-life. Calculated percent CBV change during hypercarbia was consistent with literature results from other noninvasive modalities. Equivalent percent CBV increases were f ound using spin-and gradient-echo images, suggesting proportional chan ges in blood volume for capillaries and small veins. During electrical stimulation of rat forepaw, focal CBV response to stimulation (24 +/- 4%) was significantly delayed relative to blood oxygen level dependen t (BOLD) signal after both onset and cessation of stimulation. Poststi mulus CBV decay was temporally consistent with the BOLD poststimulus u ndershoot. The use of exogenous agent increased the functional contras t-to-noise ratio relative to BOLD imaging by 5.7 +/- 1.3 at a magnetic field strength of 2 Tesla and 1.5 +/- 0.2 at 4.7 Tesla.