Predicting BOLD signal changes as a function of blood volume fraction and resolution.

The appropriate choice of resolution in fMRI remains an open question. To address this issue, we simulate the signal change between activated and resting states as a function of blood volume fraction (lambda). From these results, the relative contrast-to-noise ratio (CNR) from the resting to the activated state can be calculated as a function of resolution. We consider different vessel orientations and note that, in most cases, the most efficient scanning procedure is for low resolution imaging. To overcome this limitation, a T(1) enhancing contrast agent is proposed to increase the signal from the blood and, hence, the intravascular contribution to the BOLD effect. We show that this effect dramatically increases both the signal changes and the efficiency of high-resolution imaging and should lead to much better visualization and localization of parenchymal changes. Copyright 2001 John Wiley & Sons, Ltd.