Laser scattering by Transcranial rat brain illumination Marcelo V. P. Sousa *a , Renato Prates b , Ilka T Kato b , Caetano P. Sabino b , Luis C. Suzuki b , Martha S. Ribeiro b , Elisabeth M. Yoshimura a . a Institute of Physics, University of São Paulo, São Paulo, Brazil; b Center for Laser and Applications, IPEN-CNEN/SP, Brazil ABSTRACT Due to the great number of applications of Low-Level-Laser-Therapy (LLLT) in Central Nervous System (CNS), the study of light penetration through skull and distribution in the brain becomes extremely important. The aim is to analyze the possibility of precise illumination of deep regions of the rat brain, measure the penetration and distribution of red (λ = 660 nm) and Near Infra-Red (NIR) (λ = 808 nm) diode laser light and compare optical properties of brain structures. The head of the animal (Rattus Novergicus) was epilated and divided by a sagittal cut, 2.3 mm away from mid plane. This section of rat’s head was illuminated with red and NIR lasers in points above three anatomical structures: hippocampus, cerebellum and frontal cortex. A high resolution camera, perpendicularly positioned, was used to obtain images of the brain structures. Profiles of scattered intensities in the laser direction were obtained from the images. There is a peak in the scattered light profile corresponding to the skin layer. The bone layer gives rise to a valley in the profile indicating low scattering coefficient, or frontal scattering. Another peak in the region related to the brain is an indication of high scattering coefficient (  s ) for this tissue. This work corroborates the use of transcranial LLLT in studies with rats which are subjected to models of CNS diseases. The outcomes of this study point to the possibility of transcranial LLLT in humans for a large number of diseases. Keywords: LLLT dosimetry, rat brain illumination, Nervous System, Biophotonics, Near Infra-Red laser, Transcranial Illumination, Hippocampus, Neurology, LLLT animal model, Neurophotonics. 1. INTRODUCTION Just few years after Theodore Maiman [1] developed the first laser in 1960, it was used by Mester [2] to promote wound healing, and this is probably the first Low Level Laser Therapy (LLLT). The mechanisms of LLLT is based in photon absorption by molecules, it was first explained by Karu [3]. Laser illumination promotes DNA and RNA synthesis [4], lead protein production and increase mitochondrial production of ATP accelerating cell metabolism [5]. Nowadays LLLT is being used in branches of medicine that require reduction of inflammation, pain relief, healing, tissue regeneration or prevention of tissue death [6]. Recently remarkable results have been found in Neurology, using Transcranial LLLT, a noninvasive treatment for serious brain diseases or injuries. Transcranial LLLT improves motor recovery after strokes in rats [7] and in humans [8]; reduces significantly the recovery time in Traumatic Brain Injury (TBI) [9] with little evidence of side effects [10]. Encouraging results were obtainded for some degenerative CNS diseases as familial amyotrophic lateral sclerosis [11], Parkinson disease [12], Alzheimer disease [13] with this technique. Additionally, single neuron light stimulation [14] is connected to pain relief. Light crossing the interior of biological tissue interacts, basically, in two ways: absorption and scattering [15]. The absorption occurs when a photon interacts with an atom or molecule and the entire energy of the photon is transferred to the atom or molecule. Absorption is quantified by the absorption coefficient ( a ), which is related to the probability of this interaction in a unit of length. The scattering interactions can change both direction and energy of photons (inelastic), or only the direction (elastic scattering). Visible and near IR light interacting with biological tissue give rise mainly to elastic scattering. The scattering depends on size, shape and refraction index of the scattering center and on the wavelength of the incident light. To quantify elastic scattering two parameters are necessary: the scattering coefficient ( s ), which express the probability that scattering occurs, and the anisotropy factor (g), which is defined as the average cosine of the scattering angle. The total attenuation coefficient is  t =  a +  s . Knowledge of the penetration and distribution of light inside biological tissues is a hard problem because absorption and scattering depend on wavelength, tissue biochemistry and anatomy [16]. Numerical methods as Monte Carlo simulation [17] can be used to calculate light distribution inside tissues. Due to inhomogeneity of biological tissues, transport theory, a heuristic approach based on energy conservation, is more useful than Maxwell equations to analyze light distribution inside biological medium [16]. The amount of photons in a position  propagating in a given direction  is described by the radiative transport equation: Biophotonics: Photonic Solutions for Better Health Care III, edited by Jürgen Popp, Wolfgang Drexler, Valery V. Tuchin, Dennis L. Matthews, Proc. of SPIE Vol. 8427, 842728 © 2012 SPIE · CCC code: 1605-7422/12/$18 · doi: 10.1117/12.912616 Proc. of SPIE Vol. 8427 842728-1 Downloaded from SPIE Digital Library on 28 May 2012 to 200.136.52.139. Terms of Use: http://spiedl.org/terms