http://www.paper.edu.cn
-1-
Theoretical study light scattering and absorption by
fractal-like tissue
1
Zhifang Li, Hui Li
*
, Shulian Wu
Key Laboratory of Optoelectronic Science and Technology for Medicine, Ministry of Education,
Fujian Provincial Key Laboratory of Photonic Technology, School of Physics and OptoElectronics
Technology, Fujian Normal University, Fuzhou, Fujian, China (350007)
E-mail:hli@fjnu.edu.cn
Abstract
An analytical theory integrating the Rayleigh-Debye-Gans theory with fractal aggregate theory
(RDG-FA) for a better understanding of the optical properties of fractal-like tissue at a
high-resolution scale is present. The calculated optical properties of tissue are consistent with the
reported values. And the optical properties are related to the fractal dimension and the correlation
length. In addition, the exponents of the inverse power law spectral dependence of scattering
coefficient and reduced scattering coefficient are piecewise linearly depending on the fractal
dimension, indicating that the exponents can serve as a tools for distinguishing the different tissue.
Keywords: Rayleigh-Debye-Gans theory, fractal, optical properties
1 Introduction
Biological tissue [1], cell [2], nucleus [3], and gene [4] are composed of grain microstructure. The
microstructure can consist of different types of particles, ranging from big molecules 6.4—100nm
[4, 26], organelles 0.2-0.5um to the nuclei 3-10um in diameter [16]. Using conventional, diffraction
limited light microscopy such as confocal laser scanning microscopy, the optical resolution is
limited to ~200nm in the lateral direction and to several times worse in the axial direction [5]. The
resolution volume contains several microstructures. Each pixel in the optical image is made up of
their scattering information. Recently, a considerable amount of research has indicated that many
biological tissues are not random and have fractal-like organization [1-4,6-7]. However, a less
common perspective has gone toward understanding the physical and optical properties of
fractal-like tissue, although it is well known to be so in other areas of fractal-like aggregates [8-11].
Quantifying the optical properties of the complex fractal-like biological tissue has been actively
studied [12-18]. To our knowledge, there are two kinds of fractal models to study the optical
properties of the fractal structure of tissue. One is combining Mie theory with the fractal size
distribution of particle [12-15]. However, the approach is not available for the resolution scale
smaller than the size of the particle [17]. The other is fractal distribution of refractive-index
correlation function [16-18], which can estimate the reduced scattering coefficient, mean cosine of
the scattering angle and the phase function. A major drawback of this method is that it is impossible
to evaluate a complete set of optical properties including absorption coefficient, scattering
coefficient, reduced scattering coefficient, phase function, mean cosine of the scattering angle.
The purpose of this paper is to demonstrate that the optical properties of fractal-like tissue at a
high-resolution scale can be quantified by combining the Rayleigh-Debye-Gans scattering theory
with fractal aggregate theory (RDG-FA). In the fractal-like tissues, the optical properties depend on
the fractal dimension
f
and the correlation length
of the density correlation function. In the
section 2, the expressions linking RDG-FA to optical properties including absorption coefficient,
scattering coefficient, reduced scattering coefficient, the phase function, and mean cosine of the
1
Support by
in part by the Research Fund for the Doctoral Program of Higher Education under No.
200803940001, in part by the National Natural Science Foundation of China under Grant No.
60578056, in part by the Program for Excellent Talents in University and in part by the program for
New Century Excellent Talents in University under Grant No.NCET-04-0615 by the Ministry of
Education of China.