Abstract

Changes in the optical density of the brain measured by near infrared spectroscopy (NIRS) instruments reflect blood oxygenation changes in the various blood vessels in the brain. Light propagation in a model of the head predicted by a Monte Carlo simulation has been used to estimate the contribution of blood oxygenation change in the capillary bed and in larger blood vessels in the brain to NIRS signal. Results show that the effective partial path length in the brain tissue is much longer than that in the blood vessel on the brain surface and that blood oxygenation change in the capillary bed are the major contributors to the change in the NIRS signal.

© 2000 Optical Society of America