Analysis of photon transit time for low-power fight passing into the head,
and through both skull and brain, of human subjects allowed for tomographic
imaging of cerebral hemoglobin oxygenation based on photon diffusion theor
y; In healthy adults, imaging of changes in hemoglobin saturation during ha
nd movement revealed focal, contralateral increases in motor cortex oxygena
tion with spatial agreement to activation maps determined by functional mag
netic resonance imaging; in ill neonates, imaging of hemoglobin saturation
revealed focal regions of low oxygenation after acute stroke, with spatial
overlap to injury location determined by computed tomography scan. Because
such slow optical changes occur over seconds and co-localize with magnetic
resonance imaging vascular signals whereas fast activation-related optical
changes occur over milliseconds and co-localize with EEG electrical signals
, optical methods offer a single modality for exploring the spatiotemporal
relationship between electrical and vascular responses in the brain in vivo
, as well as for mapping cortical activation and oxygenation at the bedside
in real-time for clinical monitoring.