Monte-Carlo Simulations of BOLD Background Gradient Contributions in Diffusion-Weighted FMRI Comparison of Spin Echo and Twice-Refocused Echo Sequences

Andre Pampel¹, Thies H. Jochimsen, ¹, Harald E. Moeller, ¹

The interaction (cross-terms) between diffusion-weighting gradients and susceptibility-induced background gradient fields around vessels has an impact on ADC measurements using spin echoes. Monte-Carlo (MC) simulations integrating the Bloch equations numerically for a large number of random walks in a vascular network were used to investigate to what extent such interactions could influence the extravascular signal change observed in diffusion-weighted fMRI experiments. It is shown, that the Twice Refocused Echo sequence permits sufficient suppression of such contribution under experimentally relevant conditions.