Photon tracking in a multilayer tissue model.

A multilayer tissue description was employed in a Monte Carlo simulation of light-tissue interaction to study photon travel through skin. Paths of photons returning to the tissue surface at a certain range from the point of entry (emitter-detector spacing) were collected. The simulation demonstrates that highly absorptive discrete layers (e.g., containing melanin or blood) tend to channel photons away. As a result, the dependence of mean depth of photon penetration on wavelength is quite different from the predictions of a homogeneous tissue model. The impact upon our understanding of pulse oximetry is discussed.