Calibration of the amplitude of fMRI contrast (β) using fractional volume of gray matter: the spatial and inter-subject β calibrations

Introduction Blood oxygenation level dependent (BOLD) contrast has been widely used in fMRI study to investigate neuronal functionality. While the amplitude of BOLD contrast during the brain activation (commonly called β) is widely used to monitor neuronal activity in group analyses, β usually varies over subjects because BOLD contrast depends on a number of physiological and biophysical parameters [1]. These inter-subject β variations have been studied recently and several approaches have been proposed to calibrate these variations [2-4]. However, the calibrated fMRI is still in challenge. In this study, we propose a calibrated fMRI method based on fractional volume of gray matter (GM) measurement using FRASIER method [5], in which the spatial β variations and the inter-subject β variations are calibrated to improve sensitivity in detecting brain activation.