Abstract

A number of recent studies have focused on the possibility of using the NIR techniques to monitor a change of glucose concentration in tissue [1,2]. The basis of the method rests on the fact that a change of refractive index in the extracellular fluid due to the presence of additional glucose causes a small change in the overall scattering property of the tissue that could be detected by the NIR techniques. Chance et al [ 3] show that in lipid and yeast cell suspensions, an increase in concentration of a general solute, such as sugars and electrolytes, gives rise to a decrease in scattering factor of the suspension. These results are in good agreement with those given in Refs. 1 and 2. However, in the tissue measurement performed on a perfused rat liver, the results obtained by adding mannitol (or glucose) to the perfusate of the perfused liver displayed a behavior in contrast to those in the lipid suspensions [3] and can not be well explained by the change of only refractive index. In order to employ the NIR techniques for a broad use in noninvasive physiological monitoring, we wish to show in this paper the solute-induced correlation between optical properties in tissue and its refractive index as well as its osmolarity.

© 1996 Optical Society of America