Optical properties of human colon in the spectral range from 350 to 2500 nm

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Optical properties of human colon in the spectral
range from 350 to 2500 nm
Alexey N. Bashkatov, Vladimir S.
Rubtsov, Ekaterina A. Kolesnikova, Elina A.
Genina, Vyacheslav I. Kochubey, Sergey V.
Kapralov, Yuri V. Chalyk, Valery V. Tuchin
Saratov State University Saratov State
Medical University e-mail a.n.bashkatov_at_mail.ru
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Motivation
Development of optical method in modern medicine
in the areas of diagnostics, therapy and surgery
has stimulated the investigation of optical
properties of various biological tissues, since
the efficacy of laser treatment depends on the
photon propagation and fluence rate distribution
within irradiated tissues 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. 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 Goal of the
study is to investigate the optical properties of
human colon in the wavelength range 350-2500 nm
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Materials and Methods

• For this study twenty samples of human colon wall
  have been used. The samples keep in saline during
  2-4 hour until spectrophotometric measurements at
  temperature 4-5C. All the tissue samples has
  been cut into pieces with the area about 25?25
  mm. For mechanical support, the tissue samples
  have been sandwiched between two glass slides
• Measurement of the diffuse reflectance, total and
  collimated transmittance have been performed
  using a commercially available spectrophotometer
  LAMBDA 950 (PerkinElmer, USA) in the spectral
  range 350-2500 nm All measurements were
  performed at room temperature (about 20C)
• For estimation of absorption and scattering
  coefficients, and anisotropy factor of the tissue
  the inverse Monte Carlo method was used

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Experimental setup
The geometry of the measurements in A)
transmittance mode, B) reflectance mode. 1 - the
incident beam (diameter 1-10 mm) 2 - the tissue
sample 3 - the entrance port (square 25?16 mm)
4 - the transmitted (or diffuse reflected)
radiation 5 - the integrating sphere (IS) (inner
diameter is 150 mm) 6 - the exit port (diameter
28 mm)
The geometry of the collimated transmittance
measurements. Diameter of the incident beam is 2
mm
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Inverse Monte Carlo (IMC)
The computer program package for determination of
absorption and scattering tissue properties has
been developed. This inverse Monte Carlo method
based on the solution of direct problem by Monte
Carlo simulation and minimization of the target
function
with the boundary condition
To minimize the target function the Simplex
method described in detail by Press et al in
Numerical recipes in C the art of scientific
computing (Cambridge Cambridge University
Press, 1992) has been used. Iteration procedure
repeats until experimental and calculated data
are matched within a defined error limit (lt0.1).
Here Rdexp, Ttexp, Tcexp, Rdcalc, Ttcalc, Tccalc
are measured and calculated values of diffuse
reflectance and total and collimated
transmittance, respectively

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Inverse Monte Carlo
This method includes inverse adding-doubling
(IAD) method developed by Prahl et al (Appl.
Opt., 1993, Vol. 32(4), P. 559-568) and inverse
Monte Carlo simulations. The IAD method is widely
used in tissue optics for processing the
experimental data of spectrophotometry with
integrating spheres. This method allows one to
determine the absorption and the reduced
scattering coefficients of a turbid media from
the measured values of the total transmittance
and the diffuse reflectance. In these
calculations the anisotropy factor can be fixed
as 0.9, since this value is typical for tissues
in the visible and NIR spectral ranges. Based on
the obtained values of the tissue absorption and
reduced scattering coefficients the inverse Monte
Carlo calculations have been performed. The
inverse method includes direct problem, i.e.
Monte Carlo simulation, which takes into account
the geometric and optical conditions (sample
geometry, sphere parameters, refractive index
mismatch, etc.), and solution of inverse problem,
i.e. minimization of target function by an
iteration method. In this study, we used Monte
Carlo algorithm developed by L. Wang et al
(Computer Methods and Programs in Biomedicine,
Vol. 47, P. 131-146, 1995). The stochastic
numerical MC method is widely used to model
optical radiation propagation in complex randomly
inhomogeneous highly scattering and absorbing
media such as biological tissues. Usually the
inverse Monte Carlo technique requires very
extensive calculations since all sample optical
parameters (absorption and scattering
coefficients and anisotropy factor) unknown. To
avoid the long time calculations as a guest
values we used values of absorption and reduced
scattering coefficients obtained from
calculations performed by IAD method. For final
determination of the tissue absorption and
scattering coefficients, and the tissue
anisotropy factor minimization of the target
function has been performed.

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Inverse Monte Carlo
The flow-chart of the inverse Monte Carlo method
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Results
The typical spectra of sample of human colon
wall. Rd is diffuse reflectance Tt is total
transmittance and Tc is collimated transmittance
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Results
The absorption spectrum of the colon wall IS,
IMC, data averaged for 20 samples
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Results
The reduced scattering coefficient spectrum of
the colon wall IS, IMC, data averaged for 20
samples
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Results
The scattering coefficient spectrum of the colon
wall IS, IMC, data averaged for 20 samples
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Results
The wavelength dependence of scattering
anisotropy factor of the colon wall IS, IMC, data
averaged for 20 samples
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Monte Carlo simulation
The scheme of laser irradiation of polyps in
human colon
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Monte Carlo simulation
The optical parameters used in the simulation
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Monte Carlo simulation
Height of the polypus is 1 mm
Height of the polypus is 2 mm
The light fraction absorbed in different layers
of the colon
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Acknowledgement
Grant 224014 Network of Excellence for
Biophotonics (PHOTONICS4LIFE) of the Seventh
Framework Programme of Commission of the European
Communities
Grants 11-02-00560 and 12-02-92610-?? of
Russian Foundation of Basis Research Russian
Federation governmental contacts 02.740.11.0770,
02.740.11.0879, 11.519.11.2035, and 14.B37.21.0728