EFFECTS OF BIOPHYSICAL AND PHYSIOLOGICAL-PARAMETERS ON BRAIN ACTIVATION-INDUCED R(2)ASTERISK AND R(2) CHANGES - SIMULATIONS USING A DETERMINISTIC DIFFUSION-MODEL

A central issue in magnetic resonance imaging of human brain function using blood oxygenation level-dependent (BOLD) contrast is the accurat e interpretation of the signal changes that are observed. Using a meth od that incorporates repeated phase rotation and convolution with a sm oothing function to simulate spin diffusion in the presence of magneti c field perturbers, the dependencies of the absolute and relative chan ges in transverse relaxation rates (Delta R(2) and Delta R(2)) on bio physical and physiologic parameters were explored. First we introduce the modeling methodology. Then we simulate Delta R(2) and Delta R(2) as physiologic and biophysical parameters are modulated within the ran ges that they vary across subjects and voxels in the brain. The simula tions demonstrate that the Delta R(2) and Delta R(2) values that occu r with activation-induced changes in blood oxygenation depend most str ongly on the resting state blood volume and field strength. The Delta R(2)/Delta R(2) ratios depend most strongly on the vessel radius and spin diffusion coefficient. (C) 1995 John Wiley & Sons, Inc.