In vitro double-integrating-sphere optical properties of tissues between 630 and 1064 nm.

The optical properties (absorption and scattering coefficients and the scattering anisotropy factor) were measured in vitro for cartilage, liver, lung, muscle, myocardium, skin, and tumour (colon adenocarcinoma CC 531) at 630, 632.8, 790, 850 and 1064 nm. Rabbits, rats, piglets, goats, and dogs were used to obtain the tissues. A double-integrating-sphere setup with an intervening sample was used to determine the reflectance, and the diffuse and collimated transmittances of the sample. The inverse adding-doubling algorithm was used to determine the optical properties from the measurements. The overall results were comparable to those available in the literature, although only limited data are available at 790-850 nm. The results were reproducible for a specific sample at a specific wavelength. However, when comparing the results of different samples of the same tissue or different lasers with approximately the same wavelength (e.g. argon dye laser at 630 nm and HeNe laser at 632.8 nm) variations are large. We believe these variations in optical properties should be explained by biological variations of the tissues. In conclusion, we report on an extensive set of in vitro absorption and scattering properties of tissues measured with the same equipment and software, and by the same group. Although the accuracy of the method requires further improvement, it is highly likely that the other existing data in the literature have a similar level of accuracy.