Empirical Estimation of the Grubb Exponent Using Simultaneously Acquired CBF and Static Magnetisation Changes

Kevin Murphy¹, Ashley D. Harris¹, Richard G. Wise¹

The Grubb exponent, α, describes the non-linear relationship between CBV and CBF changes and is usually assumed to be 0.38. Increases in CBV are reflected in the static magnetisation (M0) changes of the BOLD signal. This study proposes a model to use simultaneously acquired static magnetisation and CBF measurements to determine α. A previous model by Woolrich et al., neglected M0 effects caused by extravascular spins after CBV increases. This new model accounts for both blood and non-blood effects on M0 and removes the need to assume a baseline CBV value when estimating the Grubb exponent.