Red laser attenuation in biological tissues: study of the inflammatory process and pigmentation influence Caetano P. Sabino; Daiane T. Meneguzzo; Endi Benetti, Ilka T. Kato; Renato A. Prates; Martha S. Ribeiro Centro de Lasers e Aplicações, IPEN-CNEN/SP, Brazil ABSTRACT Several studies indicate that low level laser therapy (LLLT) accelerates the healing process, however, for a determined pathology, dosimetry remains difficult to be established. To understand the tissue optical properties under different conditions is extremely relevant since the dose delivered to the target tissue is known to be critical. The skin pigmentation influence on the laser attenuation is not yet well established on different mice lineages or human ethnical groups, making the dose problematic. Along the same line, inflammatory processes may cause similar problems since the tissues in this condition change their optical properties due to inflammatory cell accumulation. This work evaluated the attenuation pattern of a HeNe laser (λ=632.8 nm) using ex vivo skin samples from Balb/C and C57BL/6 mice under inflammatory stages induced in their paw by local carrageenan inoculation. The samples were placed between two microscope slides, and a CCD camera was placed orthogonal to the beam path. The intensity distribution of the scattered light was photographed in grayscale and analyzed by ImageJ software. Our findings suggest that even slight differences of the epithelial pigmentation could result in a relevant dose loss delivered to the deeper tissues. The increase of the inflammatory cell density in the connective tissue indicated a highly scattering area also resulting in a dose loss for the deeper tissues when compared to control group. Keywords: light attenuation; red laser; inflammation; oedema; skin pigmentation 1. INTRODUCTION Low level laser therapy (LLLT) was introduced as therapeutic modality due to the required low energy densities and to the high penetration of red and infrared lasers in biological tissue. The positive clinical results of LLLT are attributed to a sequence of cellular and molecular events. The determinant factors in photochemical, photophysical or photobiological response are the wavelength, energy density, power density, chromophore concentration and the optical properties of the treated tissue (mainly absorption and scattering), as well as its physiologic state. The primary mechanisms are explained by absorption of respiratory chain’s components of light quantum, signaling a cascade of events, which leads to the final effect 1 , for example, to wound healing 2 and prevent surgical complications 3,4 reducing the hospital stay needed also reducing the chances of opportunistic infirmary infections. Although several studies have been published, light dosimetry is not largely explored in literature. In fact, a few studies report optical properties of pathological tissues 5-7 . This study was developed to determine the relative attenuation coefficient of the light intensity in skin of black and albino mice as well as we measured light attenuation following inflammatory process. The technique of imaging the light distribution allows us to obtain a qualitative attenuation pattern for the light intensity that, once known, allows the understanding of several effects of light tissue interaction and consequently, the possibility of optimization of light parameters for LLLT. Mechanisms for Low-Light Therapy VII, edited by Michael R. Hamblin, Juanita Anders, James D. Carroll, Proc. of SPIE Vol. 8211, 821105 · © 2012 SPIE · CCC code: 1605-7422/12/$18 · doi: 10.1117/12.907400 Proc. of SPIE Vol. 8211 821105-1 Downloaded from SPIE Digital Library on 28 Mar 2012 to 200.136.52.139. Terms of Use: http://spiedl.org/terms