Spatial and temporal hemodynamic study of human primary visual cortex using simultaneous functional MRI and diffuse optical tomography.

Blood oxygenation level dependent (BOLD) functional MRI and near infrared optical tomography have been widely used to investigate hemodynamic responses to functional stimulation in the human brain. In this paper, we present a complete methodology for integrating the two imaging modalities to study the underlying physiological mechanism of the hemodynamic response in primary visual cortex. Using a specially designed MRI-compatible optical probe, optical imaging was conducted using a frequency-domain near infrared spectrometer. Three-dimensional optical image reconstruction was based on diffuse optical tomography (DOT) using a perturbative approach. The sensitivity function of the forward problem was obtained using Monte Carlo simulations. From preliminary results, the spatial activation pattern of changes in deoxyhemoglobin concentration is consistent with the BOLD signal map. The patterns of oxy- and deoxyhemoglobin changes are also very similar to one another. The temporal hemodynamic response shows an increased total hemoglobin concentration, which indicates an increased cerebral blood volume (CBV) during physiological activation.