RELATIONSHIP BETWEEN TIME-RESOLVED AND NON-TIME-RESOLVED BEER-LAMBERT-LAW IN TURBID MEDIA

The time-resolved Beer-Lambert law proposed for oxygen monitoring usin g pulsed light was extended to the non-time-resolved case in a scatter ed medium such as living tissues with continuous illumination. The tim e-resolved Beer-Lambert law was valid for the phantom model and living tissues in the visible and near-infrared regions. The absolute concen tration and oxygen saturation of haemoglobin in rat brain and thigh mu scle could be determined. The temporal profile of rat brain was reprod uced by Monte Carlo simulation. When the temporal profiles of rat brai n under different oxygenation states were integrated with time, the ab sorbance difference was linearly related to changes in the absorption coefficient. When the simulated profiles were integrated, there was a linear relationship within the absorption coefficient which was predic ted for fractional inspiratory oxygen concentration from 10 to 100% an d, in the case beyond the range of the absorption coefficient, the dev iation from linearity was slight. We concluded that an optical pathlen gth which is independent of changes in the absorption coefficient is a good approximation for near-infrared oxygen monitoring.