title: Characterization of light penetration in rat tissues.
abstract: OBJECTIVE
  The goal of this study is to determine the optical properties of different rat tissues with respect to spatial intensity variation and light distribution. We are interested mainly in the wavelength of 630 nm. Nevertheless, for liver tissue we have used 514 nm and 670 nm as well.
  
  
  BACKGROUND
  In the past, many articles have been written about the interaction of lasers with rat tissues. However, the technique of imaging the light distribution allows us to obtain the spatial scattering as well as an effective attenuation coefficient for the light intensity.
  
  
  METHODS
  Slices of different 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 distribution of the scattered light. Analysis of this spatial intensity profile allowed determining the variation of the intensity as the light penetrates the tissue.
  
  
  RESULTS
  We have found that abdominal wall fat presents the lowest exponential decay when compared with liver, muscle, and kidney. The obtained values provided good data about the light distribution in those tissues when irradiated with a nondiffuse laser beam. For all tissues, we observed 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.
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo, Brasil.
authors.forename: C A
authors.initials: CA
authors.lastname: Melo
authors.forename: A L
authors.initials: AL
authors.lastname: Lima
authors.forename: I R
authors.initials: IR
authors.lastname: Brasil
authors.forename: O
authors.initials: O
authors.lastname: Castro e Silva
authors.forename: D V
authors.initials: DV
authors.lastname: Magalhães
authors.forename: L G
authors.initials: LG
authors.lastname: Marcassa
authors.forename: V S
authors.initials: VS
authors.lastname: Bagnato
mesh_terms: D000042:Absorption; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D003116:Color; D053685:Laser Therapy; D007834:Lasers; D051381:Rats