Reconstruction of imaginary part of refractive index spectrum of close-packed ?soft? pigment particles

Dubova, G. S.; Khairullina, A. Ya.; Shumilina, S. F.

doi:10.1007/bf00618281

Cited by 5 publications

(3 citation statements)

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“…On the other hand, measurements of D(λ) can enable various reverse problems of the optics of dispersed media, including the determination of the sizes of erythrocytes or their aggregates, to be solved. It is noteworthy that spectra of the optical density of whole blood were used to reproduce the imaginary part of the complex refractive index of disk-like erythrocytes [38,39].…”

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Localized light absorption by hemoglobins of an erythrocyte suspension

Barun

Иванов

2009

J Appl Spectrosc

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A correction factor accounting for the differences between the absorption spectra of an erythrocyte suspension and hemolyzed blood (hemoglobin solution) has been calculated. Erythrocytes and their aggregates are simulated by "soft" cylindrical (disk-shaped) particles. The anomalous diffraction approximation is used. At equal absorbing mass, the absorption coefficient of the suspension in the blue spectral region is shown to be capable of being several times lower than that of the solution due to localization of the absorber in erythrocytes.The hemoglobin localization effect is less important for λ em > 600 nm. Approximate analytical equations that are valid for cylindrical particles with a length-to-diameter ratio l/d > 3-4 are proposed for calculating the correction factor. More cumbersome formulas of anomalous diffraction must be used at smaller l/d values. It is shown that these formulas transform at the limit into the analytical equations. The spectra of the correction factor for cylindrical and spherical particles are compared. The simple approximation for spherical particles is demonstrated to work well for rather long aggregates when the cylinder volume-to-surface area ratio is the same as for a spherical particle. The results can be used to solve various problems of erythrocyte optics, e.g., to reproduce sizes of aggregates by measuring their spectral absorption.Introduction. Light of spectral range 300-1000 nm is absorbed in blood mainly by various forms of hemoglobins, e.g., oxy-, deoxy-, met-, sulf-, and carboxyhemoglobin among others. Variations of their molecular structures causes their absorption coefficients μ i (λ) (i is the hemoglobin form) to assume different properties depending on the wavelength of the light [1-4] although the absolute values are usually much greater than those of other blood chromophores (thrombocytes, plasma) [5, 6]. Therefore, blood absorption spectra μ b (λ) are often used for optical monitoring of its hemoglobin composition and the bulk concentration of derivatives [1,[7][8][9][10][11]. Multi-component analysis [1,3,10,11], least-squares methods, and other well developed mathematical procedures are used to deduce the concentration from the measured function μ b (λ) and known μ i (λ). The principal issue with experimental determination of μ b (λ) is the structure of the blood sample, namely, is the hemoglobin in solution after hemolysis of the blood or is it dispersed, concentrating on erythrocytes. Herein we propose a method for calculating the absorption coefficient of a suspension of erythrocytes and evaluate differences between the absorption spectra of hemoglobin suspension and solution.Current State of the Problem. The problem of finding the relationship between the absorption coefficient of a substance and its dispersed phase has been solved historically using two approaches. These are the theory of light scattering on individual particles (Maxwell's equations) and the theory of radiation transfer in the medium. It is well known in the theory of light scattering on...

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Localized light absorption by hemoglobins of an erythrocyte suspension

Barun

Иванов

2009

J Appl Spectrosc

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“…For example, such a solution exists in case of weakly absorbing optically thick media [7,8]. The procedure for the retrieval of the refractive index of weakly absorbing particles was proposed in [9]. The special case of densely packed large and small particles in the framework of the six-flux approximation of the radiative transfer theory was studied in [10,11].…”

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confidence: 99%

On the determination of the refractive index of strongly absorbing particles dispersed in a non-absorbing host medium

Kokhanovsky¹

1999

J. Phys. D: Appl. Phys.

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This paper is devoted to the development of a theoretical base for the retrieval of optical constants of large strongly absorbing particles dispersed in a non-absorbing host medium. Both single and multiple scattering regimes are studied. Particles can have a spherical shape or be non-spherical, but convex and randomly oriented. Analytical formulae relating Fresnel reflectivities for surfaces of particles to the intensity of the diffused reflected light are proposed. They are based on the single and quasi-single approximations of the radiative transfer theory. The geometrical optics approximation is used to find local optical characteristics (for example the phase function and the extinction coefficient) of turbid media under consideration.

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“…We used the diffusion approximation in [8] in order to calculate the absorption coefficient and transport scattering coefficient. This technique was shown to be highly effective for studying a suspension of erythrocytes from whole blood and biological tissues [9][10][11]. It has proven to be reliable for recovering the absorption spectrum and concentration of the photosensitizer chlorin e 6 in whole blood [7].…”

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Determination of photosensitizer concentration in biological tissues from diffuse reflectance and fluorescence

et al. 2009

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We present a fiber-optic device for noninvasive determination of the optical properties of biological tissues and photosensitizer concentration. The device developed can be used in two modes: the mode for detection of the spatial distribution of diffuse reflectance, and the fluorescence mode. We tested the device in vitro on specimens simulating tissue and on whole blood, and also in vivo on rats. We have shown that with additional modification and adaptation, the device can be used for in vivo monitoring of parameters important for photodynamic therapy.Introduction. Currently photodynamic therapy (PDT) is intensively used in clinics for treatment of cancer and other diseases [1]. The efficacy of PDT depends on the concentration of the photosensitizer and oxygen, their distribution in the tissue, the optical properties of the tissue, and the exposure dose. In this case, considerable attention has been focused on development and improvement of methods for monitoring these parameters during PDT [2, 3]. Methods based on measurement of the spatial distribution of diffuse reflectance and fluorescence are the simplest and the most economical [4,5]. We should point out that fluorescence spectroscopy is applied only in determination of the concentration of fluorescent materials, while from the spatial distribution of diffuse reflectance we can obtain data on the optical properties of biological tissues and also can determine the concentration of fluorescent chromophores in the tissues. Unfortunately, the theoretical approach based on the diffusion approximation that is used in this method has constraints on the optical properties of the tissues, and is not always effective for real biological specimens. Consequently, both methods have disadvantages, and so for practical application it is optimal to combine them.The aim of this work was to develop a fiber-optic device which would allow us to combine the methods based on measurement of the spatial distribution of diffuse reflectance and fluorescence for determining the photosensitizer (PS) concentration and also the optical properties of biological tissues.Materials and Methods. Figure 1 shows a block diagram of the fiber-optic system developed for noninvasive study of the optical properties of biological tissues and the photosensitizer concentration. Semiconductor laser photodiodes (λ = 650 nm and 635 nm) are used as the radiation source. Both laser diodes are used to detect diffuse reflectance. A laser photodiode with λ = 635 nm is used to excite fluorescence. In the fluorescence measurement, the diffuse reflectance signal at the excitation wavelength is attenuated by filters. During the measurement, using an optical fiber of thickness 200 μm with numerical aperture 0.22, laser radiation with λ = 650 nm and 635 nm is alternately delivered to the specimen.A characteristic feature and one of the advantages of this instrument is the signal detection system, which consists of a coherent optical fiber of width 5 mm, a modulator (which is a disk with slots of width 300 μm, rot...

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Reconstruction of imaginary part of refractive index spectrum of close-packed ?soft? pigment particles

Cited by 5 publications

References 5 publications

Localized light absorption by hemoglobins of an erythrocyte suspension

Localized light absorption by hemoglobins of an erythrocyte suspension

On the determination of the refractive index of strongly absorbing particles dispersed in a non-absorbing host medium

Determination of photosensitizer concentration in biological tissues from diffuse reflectance and fluorescence

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