The dependence of the macrovascular transverse R2’ relaxation and resultant BOLD fMRI signal on vascular position: A simulation study

The R2’ effect is the foundation of BOLD fMRI contrast. R2’ is disproportionately sensitive to the presence of macrovasculature, which disrupts the homogeneity of the main magnetic field (B0), resulting in BOLD signal intensities that may heavily depend on macrovascular orientation and volume but also on vascular position. We simulate the BOLD signal strength in a voxel containing macrovasculature at various vascular positions within the voxel. This simulation highlights an additional source of variability in the macrovascular contributions to R2’-weighted MRI.