PHYSIOLOGICAL-BASIS FOR BOLD MR SIGNAL CHANGES DUE TO NEURONAL STIMULATION - SEPARATION OF BLOOD-VOLUME AND MAGNETIC-SUSCEPTIBILITY EFFECTS

An NMR method is applied for separating blood volume and magnetic susc eptibility effects in response to neuronal stimulation in a rat model. The method uses high susceptibility contrast agents to enhance blood volume induced signal changes. In the absence of erogenous agent; the dominant source of signal change on neuronal activation is associated with the signal increase from the blood oxygen level dependent (BOLD) effect The relative negative contribution of blood volume changes to B OLD changes is maximally estimated to be 34%. The blood volume changes associated with median nerve stimulation (7 Hz) in the motor colter a re 26 +/- 7% and the corresponding blood susceptibility changes are 0. 021 +/- 0.006 ppm. These methods can be applied to enhance the sensiti vity of fMRI signal response and provide accurate quantitative measure s of blood volume response to stimulation.