Localized near–infrared spectroscopy and functional optical imaging of brain activity

Abstract

Changes in cerebral blood flow (CBF) and cerebral metabolic rates (CMRO 2 ) have been used as indices for changes in neuronal activity. Near–infrared spectroscopy (NIRS) can also measure cerebral haemodynamics and metabolic changes, enabling the possible use of multichannel recording of NIRS for functional optical imaging of human brain activity. Spatio–temporal variations of brain regions were demonstrated during various mental tasks. Non–synchronous behaviour of cerebral haemodynamics during the neuronsl activation was observed. Gender– and handedness–dependent lateralization of the function between right and left hemispheres was demonstrated by simultaneous measurement using two NIR instruments during the mirror–drawing task. A lack of interhemispheric integration was observed with schizophrenic patients. These observations suggest an application for NIRS in psychiatric disease management, as an addition to clinical monitoring at the bedside. A time–resolved 64–channel optical imaging system was constructed. This consisted of three picosecond laser diodes and 64 channels of TAC and CFD systems. Image reconstruction for phantom model systems was performed. Time–resolved quantitative optical imaging will become real in the very near future.