Photodynamic therapy (PDT) efficacy depends on the amount of light distribution within the tissue. However, conventional PDT does not consider the laser irradiation dose during PDT. The optical properties of biological tissues (absorption coefficient μa, reduced scattering coefficient μ′s, anisotropy factor g, refractive index, etc.) help us to recognize light propagation through the tissue. The goal of this paper is to acquire the knowledge of the light propagation within tissue during and after PDT with the optical property of PDT-performed mouse tumor tissue. The optical properties of mouse tumor tissues were evaluated using a double integrating sphere setup and the algorithm based on the inverse Monte Carlo method in the wavelength range from 350 to 1000 nm. During PDT, the μa and μ′s were not changed after 1 and 5 min of irradiation. After PDT, the μ′s in the wavelength range from 600 to 1000 nm increased with the passage of time. For seven days after PDT, the μ′s increased by 1.7 to 2.0 times, which results in the optical penetration depth decreased by 1.4 to 1.8 times. To ensure an effective procedure, the adjustment of laser parameters for the decreasing penetration depth is recommended for the re-irradiation of PDT.
To estimate the error of scattering coefficient spectrum determined by using double-integrating sphere system and
inverse Monte Carlo method, optical properties of tissue phantom were measured. The tissue phantom was composed of
hemoglobin, intralipid and gelatin. The thickness of samples
(0.1-1.0 mm) and hemoglobin concentration (0.5-4.0
mg/ml) were changed and the effects of optical properties spectra were investigated. As the results, when the value of μa
was large, μ's spectrum was not consistent with scattering theory. The higher hemoglobin concentration of samples was
the lager the errors of μ's spectra were. The thinner the sample was, the smaller the errors were. However μa spectrum
was not accurate when the sample was thin. It was predicted that when the sample thickness was 0.1 mm μ's spectrum
was accurate. And when the sample thickness was 1.0 mm, μa spectrum was accurate.
The clinical outcome of photodynamic therapy (PDT) may be improved by the accurate knowledge about the light
distribution within the tissue. Optical properties [absorption coefficient (μa), scattering coefficient (μs), anisotropy factor
(g), refractive index, etc.] of tissues help us realizing a light propagation through the tissue. The aim of this study is
acquisition of the knowledge of light propagation within tissue with the optical property of mouse tumor tissue
performed PDT. We evaluated the optical property of mouse tumor tissue before and after PDT using the double
integrating sphere setup and algorithms based on the inverse Monte Carlo method in the wavelength range from 350 to
1000 nm. During PDT, the reduced scattering coefficient spectra were decreased entirely after 5 and 10 min irradiation.
1, 2, 7 days after PDT, the absorption coefficient was increased in the wavelength range from 400 to 660 nm. And, the
reduced scattering coefficient at the wavelength of 664 nm was increased with the passage of time. These results are used
for medical diagnostic applications for the quantitative assessment of the PDT effect. 7 days after PDT, the reduced
scattering coefficient at the wavelength of 664 nm was increased significantly from 0.64 mm-1 to 1.24 mm-1, which
results in the optical penetration depth decreased from 1.49 mm to 0.84 mm, respectively. To ensure the effective
procedure, an adjustment of the laser parameter for the decreasing penetration depth is recommended for a second PDT.
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