A THEORY OF DIFFUSE LIGHT-SCATTERING BY LUNGS

A theoretical treatment of backscattered light from the interior of a lung illuminated by a thin beam of light normally incident on the pleural surface is presented. An approximate formula is developed describing how the backscattered intensity varies with distance from the point of light entry. This depends markedly on the optical mean free path and on the effective extinction coefficient. The optical mean free path was related to the mean alveolar size. This relationship depends primarly on septal reflection and refraction. Reflection is treated quantitatively. Refraction is much more difficult and may have to be approached empirically. The rudiments of a technique with implications for the possibility of dynamic stereology are presented.