Proceedings - Viện Vật lý

_________________________________________________________________________________Những tiến bộ trong Quang học, Quang tử, Quang phổ và Ứng dụng. 8/2006, Cần Thơ, Việt NamTHEORETICAL CALCULATION OF SCATTERING PARAMETERSOF SOME BIOLOGICAL TISSUES WHEN IRRADIATED BYLASER BEAMS OF WAVELENGTHS OF 780nm AND 940nmTrần Thị Ngọc Dung * , Trần Minh TháiDepartment of Biomedical Engineering Physics, Faculty of Applied SciencesUniversity of Technology – Ho Chi Minh City National University.268 Lý Thường Kiệt, Q10, TP Hồ Chí MinhAbstract: Laser beams of 780nm and 940nm wavelengths have been used toirradiate biological tissues in optoacupuncture and optotherapy. In tissue, atoptical window (600nm-1100nm), scattering is the principal mechanism to affectthe light propagation. When applying laser into disease treatment, the simulationof the photon propagation in tissues could help for the quantitative determinationof the distribution of photon energy in tissues, which enables us to evaluate thepropagation depth of the laser beam in tissues. To simulate the photonpropagation, we need optical parameters of tissues, including scattering crosssection,scattering coefficient, anisotropy. In this article, the scattering crosssectionsof some cell structures such as cell nucleus, mitochondria, collagenfibrils, collagen fibers, and melanosomes are calculated. And then, the scatteringcoefficients of skin, brain, gray matter and white matter are determined andcompared to the experimental values reported in Biomedical Photonics Handbook,Edit.Tuan Vo-Dinh, SPIE Press, 2002. The calculated values are appropriate tothe experimental values. The theoretical calculation of scattering parameters oftissue at a given wavelength provides us the data necessary for the simulation oflaser beam propagation in case there are no experimental data reported at thewavelength interested.Keywords: scattering, scattering cross-section, anisotropy, scattering coefficient.1. IntroductionAs an electromagnetic (EM) wave encounters a tissue, the electrons inmolecules constituting the tissue will be perturbed with the same frequency of theincident wave and form induced dipole moments. The induced dipoles generate EMwaves and so create a scattered field.Scattered processes have an important role in medical diagnostics andtreatment. Light scattering by spherical object absorbing or non absorbing isdescribed by Mie scattering theory, which is proved applicable to all size ofscatteres. When the size of scatterers is small compared to the wavelength of thelight, the scattering is in Rayleigh scattering limit. When the size of scatterer is*E-mail: pfiev@hcmut.edu.vn; ttndung@hcmut.edu.vn248