Establishment of the Measurement lhchnique for Cerebral Blood Flow and Metabolism during Brain Activation using MRI and Nearinfrared Spectroscopy.

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We have developed a simultaneous measurement system using functional magnetic resonance imaging (fMRI) and near-infrared spectroscopy (NIRS) technique. Twenty-two normal volunteers aged 21 to 43 were studied with a 3T MRI system (GEYMS Signa Horizon LX) and an optical imaging system (Hitachi ETG-100). Optical cable-bundle was extended to the MR head-coil to set up the simultaneous acquisition system. Various photic patterns and durations were used for the visual activations. The temporal characteristics of blood oxygenation level-dependent (BOLD) responses to brief visual stimulation of the human primary visual cortex (V1) were investigated using an event-related functional magnetic resonance imaging (ER-fMRI) technique. The magnitude and extent of the BOLD response were examined by changing the stimulus duration of a reversing checkerboard between 1 to 6 secs. In addition, the relationship between measured and predicted BOLD responses was evaluated. Results show that the peak height and the area above the baseline increased linearly as a function of stimulus duration. Retinotopic and event-related studies showed that the localization and linearity of the responses with these two systems were nearly identical. The fMRI contrast (BOLD) uses deoxyhemoglobin information, and NIRS uses both oxyhemoglobin and deoxyhemoglobin dynamics (the sum of these are named total hemoglobin, related to cerebral blood volume). Simultaneous measurement system provides and integrates the spatial and temporal dynamics with respect to the brain physiological parameters (e.g., CBF, CBV, and CMRO2).