Optical properties of the human tissue
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Transcript Optical properties of the human tissue
Saratov State
University
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Department of Optics &
Biophotonics
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Absorption and scattering properties of
human eye sclera
Alexey N. Bashkatov, Elina A. Genina,
Vyacheslav I. Kochubey, Tatyana G. Kamenskikh,
Valery V. Tuchin
Department of Optics and Biophotonics
Saratov State University
Saratov State Medical University
e-mail: [email protected]
Saratov Fall Meeting 2011
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 of optical properties of human
eye sclera in the wavelength range 400-2000 nm
Saratov Fall Meeting 2011
Materials and Methods:
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Saratov State
University
______________________________________________
Department of Optics &
Biophotonics
For this study twenty samples of human eye sclera 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 2525 mm2. 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 PerkinElmer LAMBDA 950 in the spectral range
400-2000 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.
Saratov Fall Meeting 2011
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 2516 mm);
4 - the transmitted (or diffuse
reflected) radiation; 5 - the integrating
sphere (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.
Saratov Fall Meeting 2011
Saratov State
University
Inverse Monte Carlo
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__________________________________________________
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 (Press W.H., et al. 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.
Saratov Fall Meeting 2011
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 (Prahl S.A.,
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 (Wang L., 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 2011
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 2011
Saratov State
University
Results:
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Department of Optics &
Biophotonics
0.1
0.01
1E-3
Rd
Tt
Tc
1E-4
1E-5
400
800
1200
1600
2000
Wavelength, nm
The typical spectra of sample of human eye sclera. Rd is diffuse
reflectance; Tt is total transmittance and Tc is collimated transmittance
Saratov Fall Meeting 2011
Saratov State
University
Results:
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______________________________________________
Department of Optics &
Biophotonics
Absorption coefficient, 1/cm
70
60
50
40
30
20
10
0
400
800
1200
1600
2000
Wavelength, nm
The absorption spectrum of the scleral tissue
IS, IMC, data averaged for 20 samples
Saratov Fall Meeting 2011
Saratov State
University
Results:
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______________________________________________
Department of Optics &
Biophotonics
Reduced scattering coefficient, 1/cm
100
5
's() = 2.411*10 /
1.325
80
60
40
20
0
400
800
1200
1600
2000
Wavelength, nm
The reduced scattering coefficient spectrum of the scleral tissue
IS, IMC, data averaged for 20 samples
Saratov Fall Meeting 2011
Saratov State
University
Results:
__________________________________________________
______________________________________________
Department of Optics &
Biophotonics
Scattering coefficient, 1/cm
220
200
180
160
140
120
100
400
800
1200
1600
2000
Wavelength, nm
The scattering coefficient spectrum of the scleral tissue
IS, IMC, data averaged for 20 samples
Saratov Fall Meeting 2011
Saratov State
University
Results:
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______________________________________________
Department of Optics &
Biophotonics
1.0
Anisotropy factor
0.9
0.8
0.7
0.6
0.5
400
800
1200
1600
2000
Wavelength, nm
The wavelength dependence of scattering anisotropy factor of the scleral tissue
IS, IMC, data averaged for 20 samples
Saratov Fall Meeting 2011
Acknowledgement:
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Saratov State
University
______________________________________________
Department of Optics &
Biophotonics
Grant #224014 Network of Excellence for
Biophotonics (PHOTONICS4LIFE) of the Seventh
Framework Programme of Commission of the
European Communities
Grant # 10-02-90039 Бел_а of Russian Foundation of
Basis Research
Russian Federation governmental contacts
02.740.11.0484, 02.740.11.0770, and 02.740.11.0879
Saratov Fall Meeting 2011