Transcript Presentation

Saratov State
University
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Department of Optics &
Biophotonics
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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: [email protected]
Saratov Fall Meeting 2012
Saratov State
University
Motivation:
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Department of Optics &
Biophotonics
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
Saratov Fall Meeting 2012
Materials and Methods:
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Saratov State
University
______________________________________________
Department of Optics &
Biophotonics
 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 4-5°C. 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
20°C)
 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
Saratov State
University
______________________________________________
__________________________________________________
Department of Optics &
Biophotonics
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)
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Saratov State
University
______________________________________________
Department of Optics &
Biophotonics
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
F  a , s , g    Rdexp  Rdcalc  a , s , g    Tcexp  Tccalc  a , s , g    Tt exp  Tt calc  a , s , g  
2
2
2
with the boundary condition 0  g  0.98
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 (<0.1%). 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
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Saratov State
University
______________________________________________
Department of Optics &
Biophotonics
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.
Saratov Fall Meeting 2012
Inverse Monte Carlo
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Saratov State
University
______________________________________________
Department of Optics &
Biophotonics
The flow-chart of the inverse Monte Carlo method
Saratov Fall Meeting 2012
Saratov State
University
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Results:
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Department of Optics &
Biophotonics
1
0.1
0.01
1E-3
Rt
Tt
Tc
1E-4
0
500
1000
1500
2000
2500
Wavelength, nm
The typical spectra of sample of human colon wall. Rd is diffuse reflectance;
Tt is total transmittance and Tc is collimated transmittance
Saratov Fall Meeting 2012
Saratov State
University
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Results:
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Department of Optics &
Biophotonics
Absorption coefficient, 1/cm
60
50
40
30
20
10
0
0
500
1000
1500
2000
2500
Wavelength, nm
The absorption spectrum of the colon wall
IS, IMC, data averaged for 20 samples
Saratov Fall Meeting 2012
Saratov State
University
Results:
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Department of Optics &
Biophotonics
Reduced scattering coefficient, 1/cm
200
160
120
80
40
0
0
500
1000
1500
2000
2500
Wavelength, 1/cm
The reduced scattering coefficient spectrum of the colon wall
IS, IMC, data averaged for 20 samples
Saratov Fall Meeting 2012
Saratov State
University
Results:
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Department of Optics &
Biophotonics
Scattering coefficient, 1/cm
360
320
280
240
200
160
120
80
40
0
500
1000
1500
2000
2500
Wavelength, nm
The scattering coefficient spectrum of the colon wall
IS, IMC, data averaged for 20 samples
Saratov Fall Meeting 2012
Saratov State
University
______________________________________________
Results:
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Department of Optics &
Biophotonics
1.0
Anisotropy factor
0.8
0.6
0.4
0.2
0.0
0
500
1000
1500
2000
2500
Wavelength, nm
The wavelength dependence of scattering anisotropy factor of the colon wall
IS, IMC, data averaged for 20 samples
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Saratov State
University
Monte Carlo simulation:
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Department of Optics &
Biophotonics
The scheme of laser irradiation of polyps in human colon
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Saratov State
University
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Monte Carlo simulation:
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50
Polyp
Wall of colon
Muscle
45
Absorption coefficient, 1/cm
Department of Optics &
Biophotonics
40
35
30
25
20
15
10
5
0
Polyp
Wall of colon
Muscle
200
400
800
1200
1600
2000
Wavelength, nm
1.0
180
0.9
160
0.8
140
Anisotropy factor
Scattering coefficient, 1/cm
220
120
100
80
0.7
0.6
0.5
0.4
60
400
800
1200
1600
2000
Wavelength, nm
0.3
0.2
200
The optical parameters used in the simulation
Polyp
Wall of colon
Muscle
400
600
800
1000
1200
1400
1600
1800
2000
2200
Wavelength, nm
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University
______________________________________________
Monte Carlo simulation:
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0.9
0.8
0.9
Polyp
Wall of the colon
Muscle
0.8
0.7
Absorbed fraction
0.7
Absorbed fraction
Department of Optics &
Biophotonics
0.6
0.5
0.4
0.3
0.6
0.5
0.4
0.3
0.2
0.2
0.1
0.1
0.0
0.0
400
800
1200
1600
2000
Polyp
Wall of the colon
Muscle
400
1200
1600
2000
Wavelength, nm
Wavelength, nm
Height of the polypus is 1 mm
800
Height of the polypus is 2 mm
The light fraction absorbed in different layers of the colon
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Acknowledgement:
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Saratov State
University
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Department of Optics &
Biophotonics
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-КО 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
Saratov Fall Meeting 2012