Optical properties of parietal peritoneum in the spectral range 3502500 nm Marina D. Kozintsevaa*, Alexey N. Bashkatova, Vyacheslav I. Kochubeya, Elina A. Geninaa, Sergey Yu. Gorodkovb, Dmitry A. Morozovc, Valery V. Tuchina a
Department of Optics and Biophotonics of N.G. Chernyshevsky Saratov State University, Saratov, Russia, b Saratov State Medical University named after V.I. Razumovsky, c Moscow State ScientificResearch Institute of Pediatrics and Children Surgery ABSTRACT The wide application of optical methods in the areas of diagnostics, therapy and surgery of modern medicine has stimulated the investigation of optical properties of various biological tissues. Numerous investigations related to determination of tissue optical properties are available; however, the optical properties of many tissues have not been studied in a wide wavelength range. In this work the optical properties of parietal peritoneum in the wavelength range 350-2500 nm were measured. Measurement of the diffuse reflectance, total and collimated transmittance were performed using LAMBDA 950 (Perkin Elmer, USA) spectrophotometer with an integrating sphere, and values of absorption and scattering coefficients, and the scattering anisotropy factor were calculated by inverse Monte Carlo Method. Keywords: parietal peritoneum, optical properties of biological tissues, integrating sphere technique, inverse Monte Carlo method
1. INTRODUCTION The surgical intervention into human body is inevitable method of treatment in the case of many diseases. However, on the early stage of many diseases, it’s possible to develop new methods of diagnostics and treatments without surgery. The knowledge of tissue optical properties is necessary for the development of the novel optical technologies of photodynamic and photothermal therapy, optical tomography, optical biopsy, and etc., and this is the one of the key moments for creation of the mathematical models that adequately describe the propagation of light in biological tissues that is very important part of the development of new optical methods that could be used in various fields of biology and medicine1,2. There is significant number of papers dealed with the determination of optical parameters of biological tissues3,4-7, however, the optical properties of many tissues have not been studied in a wide wavelength range. The goal of this study is to determine the scattering and absorption properties of the parietal peritoneum tissue in the spectral range of 350-2500 nm, because it has a fundamental importance for the development of optical diagnostics, photodynamic and photothermal therapy of various diseases.
2. MATERIAS AND METHODS 2.1. Materials The experiments were performed on male outbred white laboratory rats; the weight was on average 200-300 g. For the study 13 samples of the parietal peritoneum mucous membrane, 10 samples of the parietal peritoneum muscle membrane and 14 samples of the whole parietal peritoneum tissue (mucous membrane + muscle membrane) were used. The samples kept in saline during 3-4 hours until spectrophotometric measurements at temperature 4-5°C. All the tissue samples were cut into pieces with the area about 8 ± 1 cm2. For mechanical support, the tissue samples were sandwiched *
*
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Saratov Fall Meeting 2013: Optical Technologies in Biophysics and Medicine XV; and Laser Physics and Photonics XV, edited by Elina A. Genina, Vladimir L. Derbov, Igor Meglinski, Valery V. Tuchin, Proc. of SPIE Vol. 9031, 90310E © 2014 SPIE · CCC code: 1605-7422/14/$18 · doi: 10.1117/12.2051685 Proc. of SPIE Vol. 9031 90310E-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/09/2014 Terms of Use: http://spiedl.org/terms
between two glass slides. The accuracy of each measurement was ± 50 μm. The average thickness of the samples was 0.79 ± 0.2 mm for parietal peritoneum mucous membrane, 2.42 ± 0.35 mm for parietal peritoneum muscle membrane and 3.81 ± 0.2 mm for entire parietal peritoneum tissue (mucous membrane + muscle membrane). 2.2. Methods Measurements of the diffuse reflectance, total and collimated transmittance were performed using a commercially available spectrophotometer LAMBDA 950 (PerkinElmer, USA) with an integrating sphere (Figure 1) in the spectral range 350-2500 nm. All measurements were performed at room temperature (about 20 °C). The sizes of the incident light beam on the sample were: for the total transmittance measurement - 2×4 mm, for the diffuse reflection measurement - 2×2 mm, for the collimated transmittance measurement - 2×4 мм. The scanning rate was 5 nm/sec. Experiments were provided with tissue samples that were fixed between two glass slides (Figure 2). A specially designed accessory was used for measuring of the collimated transmittance that consists of a holder, where the sample tissue was fixed in, and of a system of four diaphragms.
Figure 1. A general view of the spectrophotometer LAMBDA 950.
Figure 2. Samples of the whole parietal peritoneum (mucous membrane + muscle membrane), parietal peritoneum mucous membrane and parietal peritoneum muscle membrane sandwiched between two glass slides.
For estimation of absorption ( μ a ), and scattering coefficients ( μ s ), and anisotropy factor (g) of the tissue the inverse Monte Carlo method was used. Flow-chart of the inverse Monte Carlo method is presented in Figure 3.
Proc. of SPIE Vol. 9031 90310E-2 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/09/2014 Terms of Use: http://spiedl.org/terms
Inverse adding – doubling (IAD) method μa, μs, g
Start parameters
Monte – Carlo simulation; Sample and beam geometry
Variation μa, μs, g with Simplex method
Rd, Tt, Tc
Measurement Rd, Tt, Tc
no
Difference smaller error threshold? yes
Accept μa, μs, g Figure 3. The flow-chart of the inverse Monte Carlo method.
2.3. Inverse Monte Carlo method (IMC) The computer program was developed for determination of absorption and scattering tissue properties. This inverse Monte Carlo method based on the solution of direct problem by Monte Carlo simulation and minimization of the target function
(
F ( μ a , μ s , g ) = Rd − Rd exp
calc
(μ
a
, μs , g )
) + (T 2
c
exp
− Tc
calc
(μ
a
, μs , g )
) + (T 2
t
exp
− Tt
calc
(μ
a
)
, μs , g ) , 2
(1)
with the boundary condition 0 ≤ g ≤ 0.99 . To minimize the target function the Simplex method described in detail by Press et al.8 was used. Iteration procedure repeated until experimental and calculated data were matched within a predefined calculation accuracy (
