Characterization of light penetration in rat tissues

Objective: The goal of this study is to determine the optical properties of different rat tissues with respect to spatial intensity variation and ligh t distribution. We are interested mainly in the wavelength of 630 nm. Never theless, for liver tissue we have used 514 nm and 670 nm as well. Backgroun d Data: In the past, many articles have been written about the interaction of lasers with rat tissues. However, the technique of imaging the light dis tribution allows us to obtain the spatial scattering as well as an effectiv e attenuation coefficient for the light intensity. Methods: Slices of diffe rent rat tissues were placed between two microscope slide mounts (spaced by 3 mm). A laser beam was irradiated on the sandwiched tissue. A CCD camera placed on the side, orthogonal to the beam path, recorded the intensity dis tribution of the scattered light. Analysis of this spatial intensity profil e allowed determining the variation of the intensity as the light penetrate s the tissue. Results: We have found that abdominal wall fat presents the l owest exponential decay when compared with liver, muscle, and kidney. The o btained values provided good data about the light distribution in those tis sues when irradiated with a nondiffuse laser beam. For all tissues, we obse rved a spherical light distribution and exponential decay. Cirrhotic liver shows much stronger decay than healthy liver. These results are useful for several applications of laser for biostimulation a phototherapy.