Effects of biophysical and physiologic parameters on brain activation‐induced R2* and R2 changes: Simulations using a deterministic diffusion model

Abstract

AbstractA central issue in magnetic resonance imaging of human brain function using blood oxygenation level‐dependent (BOLD) contrast is the accurate interpretation of the signal changes that are observed. Using a method that incorporates repeated phase rotation and convolution with a smoothing function to simulate spin diffusion in the presence of magnetic field perturbers, the dependencies of the absolute and relative changes in transverse relaxation rates (δR2* and δR2) on biophysical and physiologic parameters were explored. First we introduce the modeling methodology. Then we simulate δR2* and δR2 as physiologic and biophysical parameters are modulated within the ranges that they vary across subjects and voxels in the brain. The simulations demonstrate that the δR2* and δR2 values that occur with activation‐induced changes in blood oxygenation depend most strongly on the resting state blood volume and field strength. The δR2*/δR2 ratios depend most strongly on the vessel radius and spin diffusion coefficient.