STUDY ON BRAIN HEMODYNAMICS BY SIMULTANEOUS MEASUREMENT OF FUNCTIONAL MRI AND NEAR-INFRARED SPECTROSCOPY

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The purpose of this study was to understand brain hemodynamics in response to neuronal activation using simultaneous measurement of functional MRI (fMRI) and near-infrared spectroscopy (NIRS). Firstly, to improve detection of areas reflecting hemodynamic changes, artifacts in fMRI were analyzed. Secondly, probes of MRS were implemented into MRI bore for simultaneous measurements of MRI and NIRS during finger tapping tasks. Based on the observed results of two different techniques, the brain hemodynamics was explained.(1) We introduced a new analysis of artifacts in fMRI based on thermal noise intensity to quantitatively evaluate the efficacy of countermeasures against artifacts. It was demonstrated that both the task-related motion and the major influence of respiration are global head motion, which can be corrected by the motion correction software (SPM), having their own properties of time-intensity changes in pixels of the artifacts. True reduction of the influence of pulsation is essential for artifact-free fMRI.The efficacy of the motion correction of 8PM was also evaluated quantitatively. A pitfall dependent on image-spatial resolution was revealed. One-mm spatial resolution is necessary for the sufficient motion correction.(2) The simultaneous measurement of fMRI and NIRS showed that depicted areas reflecting BOLD type changes in fMRI were explained by changes of deoxygenated hemoglobin (deoxyHb) derived from NIRS.Probe positions observing dominant changes of oxygenated hemoglobin and deoxyHb were displaced slightly, indicating the variety of vascularity. Since NIRS results by a single probe suffer from spatial ambiguity of measurements, it is sometimes hard to derive a hemodynamic model. Improvement of spatial resolution in NIRS is necessary for further investigation of brain hemodynamics in response to neuronal activation.