皮肤组织容积脉搏波400~1000 nm光谱特性仿真研究

根据皮肤组织解剖结构特性建立了六层层状模型,并给出了皮肤组织各层的特性参数;考虑了氧合血红蛋白和还原血红蛋白的吸收特性,依据皮肤组织各层的水、血、脂肪、血氧饱和度含量以及血管大小给出了皮肤组织各层的光谱吸收系数;对不同波长散射系数做了适当简化,给出了皮肤组织各层的光谱散射系数。利用蒙特卡罗方法仿真血管组织在收缩与舒张两种状态下, 400~1 000 nm波长光在皮肤组织多层模型中的传输过程,并通过统计大量光子的分布特性,获得了皮肤组织光谱反射系数,并利用模拟所得的两种状态下的反射系数计算得到了光谱容积脉搏波幅度。仿真结果表明,当入射光强一定时,绿光的容积脉搏波幅度优于红光和蓝光。通过计算不同波长光沿皮肤组织深度方向光能流率衰减为1/e时对应的皮肤组织深度,获得了皮肤组织光谱穿透深度。结果显示,血管舒张状态下蓝光和绿光的穿透深度较小,蓝光大部分只能达到表皮层,绿光能到达微循环层,红光可直达真皮层。考虑到光在皮肤组织中传播包含了一个从收缩到舒张的动态过程,基于此,根据穿透深度定义了脉搏波信号产生深度,利用血管舒张与收缩两种不同状态下的穿透深度计算得到了光谱产生深度。结果表明,不同波长光产生深度大于其穿透深度,蓝光产生深度较浅,且其受到的血液吸收调制较小,因而其获得的脉搏信号易受噪声干扰;红光的容积脉搏波产生深度较大,但是相比于绿光其受血液吸收调制较小,且绿光产生深度足够达到真皮血管层,因而红光容积脉搏波的幅度小于绿光。上述仿真结果明确了皮肤组织部分光谱特性,为皮肤组织多光谱容积脉搏波的精确获取及其他相关研究提供了一定的理论基础。     

Absorption spectra and light penetration depth of normal and pathologically altered human skin

A three-layered skin model (stratum corneum, epidermis, and dermis) and engineering formulas for radiative transfer theory are used to study absorption spectra and light penetration depths of normal and pathologically altered skin. The formulas include small-angle and asymptotic approximations and a layer-addition method. These characteristics are calculated for wavelengths used for low-intensity laser therapy. We examined several pathologies such as vitiligo, edema, erythematosus lupus, and subcutaneous wound, for which the bulk concentrations of melanin and blood vessels or tissue structure (for subcutaneous wound) change compared with normal skin. The penetration depth spectrum is very similar to the inverted blood absorption spectrum. In other words, the depth is minimal at blood absorption maxima. The calculated absorption spectra enable the power and irradiation wavelength providing the required light effect to be selected. Relationships between the penetration depth and the diffuse reflectance coefficient of skin (unambiguously expressed through the absorption coefficient) are analyzed at different wavelengths. This makes it possible to find relationships between the light fields inside and outside the tissue. __________ Translated from Zhurnal Prikladnoi Spektroskopii Vol. 74, No. 3, pp. 387–394, May–June, 2007.     

Depth distributions of light action spectra for skin chromophores

Light action spectra over wavelengths of 300–1000 nm are calculated for components of the human cutaneous covering: melanin, basal (bloodless) tissue, and blood oxy- and deoxyhemoglobin. The transformation of the spectra with depth in biological tissue results from two factors. The first is the wavelength dependence of the absorption coefficient corresponding to a particular skin chromophore and the second is the spectral selectivity of the radiation flux in biological tissue. This factor is related to the optical properties of all chromophores. A significant change is found to take place in the spectral distribution of absorbed radiant power with increasing depth. The action spectrum of light for the molecular oxygen contained in all components of biological tissue is also studied in the 625–645 nm range. The spectra are found to change with both the volume fraction of blood vessels and the degree of oxygenation of the blood. These results are useful for analyzing processes associated with optical absorption that are possible mechanisms for the interaction of light with biological tissues: photodissociation of oxyhemoglobin and the light-oxygen effect.     

Noninvasive optical method for determining the scattering coefficients and the specific volume of blood in biological tissue <Emphasis Type="Italic">in vivo</Emphasis>

We propose a method for determining the scattering coefficients of biological tissue and changes in the relative volume of blood. The method is based on the difference of the parameters of optical radiation that has passed through a biological tissue and the radiation scattered by it in the opposite direction. The obtained correlations between the ratio of the scattered light modulation coefficients at two wavelengths and the biotissue parameters permits determination of the tissue characteristics directly in the living organism. The scattering coefficients at different wavelengths and the values of the relative volume of blood for different anatomical zones and its changes during physiological loads have been calculated.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 119–123, January–February, 2005.     

Estimate of the Contribution of Localized Light Absorption by Blood Vessels to the Optical Properties of Biological tissue

A simple analytical procedure of considering localized light absorption by blood vessels and its effect on the absorption characteristics of multicomponent biological tissue is proposed. The final results are presented in the form of a single integral of elementary functions. A comparison of the estimates obtained with data in the literature shows their good agreement. The limiting cases of random and ordered arrangement of vessels are considered. It was shown that, in the blue spectral range, the absorption coefficient of biological tissues can reach saturation when it ceases to be dependent on the optical characteristics of blood and is determined only by the diameter of vessels and their volume concentration. The depth of light penetration into tissue and the reflection coefficient of tissue are estimated for both a localized and a homogeneously distributed absorber. Possible biomedical applications of the results obtained are illustrated.     

Estimation of the Effective Measuring Volume of Single-Fibre Reflection Probes for solid volume concentration measurements

The working principle of the single-fibre reflection (SFR) probe is that light emitted by a laser diode is guided into the measuring volume by the same fibre which receives the proportion of light reflected by the particles in the vicinity of the probe tip and transmits it back to a photosensitive element. In contrast to other configurations of fibre optical probes, the SFR probe is characterized by an unambiguous calibration graph over the entire range of solid volume concentration values. SFR probes have been successfully applied to different kinds of multiphase flow systems, e.g. fluidized beds, pneumatic conveying lines, elutriators and thickeners. A particular question for the interpretation of measurements has always been the effective size of the measuring volume, which is mainly determined by the solid volume concentration. In this paper a simplified mathematical model of the signal generation by backscattering of the emitted light at the particle surfaces is given. The theory takes into account the average optical properties of the solids and their particle size distributions. The particle properties are determined on the basis of this model, which finally delivers the shape, size and depth of the effective measuring volume. For particle sizes between 30 and 120 μm the depth of the measuring volume of a 600-μm fibre probe is between 0.2 mm for solid concentrations near the fixed-bed state and approximately 4 mm for solid volume concentrations as low as 0.1 vol.-%.     

Analysis of Light Propagation in a Realistic Head Model by a Hybrid Method for Optical Brain Function Measurement

Near infrared spectroscopy (NIRS) is used to measure the change in blood volume and oxygenation in the brain cortex induced by functional brain activation. The development of an adequate model to calculate light propagation in the head is very important because the light is strongly scattered in the tissue and this causes ambiguity in the volume of tissue interrogated with a source–detector pair of the NIRS instrument. In this study, a two-dimensional realistic head model is generated from a MRI scan of a human adult head. The light propagation in the head model is calculated by the hybrid Monte Carlo–diffusion method to obtain the change in detected intensity caused by a focal absorption change in the grey matter or in the white matter to discuss the relationship between the depth of the activated region and the sensitivity of the NIRS signal. The sensitivity to the activated region in the white matter steeply decreases with an increase of the depth of the activated region because the spatial sensitivity profile is mainly confined to the grey matter. The contribution of the focal brain activity to the NIRS signal is determined by not only the depth of the activated region from the head surface but also the depth of the activated region from the brain surface.     

Depth visualization of a local blood region in skin tissue by use of diffuse reflectance images

A simple method is proposed for visualizing the depth distribution of a local blood region in skin tissue by using diffuse reflectance images at two isosbestic wavelengths of hemoglobin, 420 and 585 nm. Monte Carlo simulation of light transport specifies a relation between optical densities and the depth of the region under given concentrations of melanin in the epidermis and blood in the dermis. Phantom and in vivo experiments were performed to show the usefulness of the method.     

基于反射法的光纤位移 振动传感器优化设计

采用非相干光作为光源,以平面镜为反射面,对光纤位移 振动传感器的性能进行研究。推导出光纤输出功率与测量距离的解析表达式,并详细探讨了不同光纤半径、光纤数值孔径、发射光纤和接收光纤间距、发射光纤和接收光纤轴线夹角下输出功率比与测量距离之间的内禀关系。仿真结果表明:光纤半径越小,光纤间距越大,可以测试的距离范围越小;光纤数值孔径、光纤轴线夹角越小,可以测试的距离范围越小。通过分析不同情况下,输出功率比随测量距离变化的关系,可以在实际工程应用中根据测量需要选择设计合适的传感器。此外,还对测量误差进行了分析,得到光纤轴线夹角越小,测量距离的范围越大,误差率越小,当光纤轴线夹角为0.25时,误差率约为1%。     

哺乳动物五种离体组织光学特性的测量

光在哺乳动物组织中的传输依赖于组织体的光学特性,组织的光学特性是由吸收系数、散射系数和散射相位函数决定的。我们设计并实现了哺乳动物5种离休组织光学特性的测量。对实验方法和技术作了较大的改进,联合组织体漫反射特性和光能流率的测定,获得了满意的结果:光穿透深度δ=1.1～5.06mm,吸收系数μ_a=0.4～1.6cm^-1.有效散射系数μ_s(1-g)=2.7～17.7cm^-1.这种测量方法可用于人体组织光学特性的测量。     

Adaptive exponential approximation of optical density ratio using third-order regression equations for depth profiling of a blood inclusion in a skin tissue model

We propose the use of the third-order multiple regression equations in approximating an optical density ratio with an adaptive exponential function for measuring depth and thickness of a blood inclusion embedded in a skin tissue model. To ensure accuracy of the exponential approximation, we investigated numerically various relations of optical density ratios versus depth and thickness, on the basis of Monte Carlo simulations for a layered skin tissue model. The third-order multiple regression analysis based on the relations above was used to derive regression equations for the determination of depth and thickness. Experiments with skin tissue phantoms were used to assess this approach.     

Estimation of the spectral absorption of light by components of human skin

The spectra of the absorption coefficients of external radiation by basic chromophores of human skin, such as melanin, basic tissue, and blood (including oxy- and deoxyhemoglobin), are studied in the wavelength range of 300–1000 nm. For estimates, analytical methods of the theory of light transfer are used, which take into account the multilayer structure of a biological tissue, multiple light scattering in a medium, and multiple rereflections of radiation between layers. The calculated spectra are compared with the wavelength dependences of the absorption indices of these components available from the literature. It is shown that the spectral behaviors of the coefficients and indices of absorption strongly differ, which is related to the selectivity of the optical properties of a biological tissue. The possibilities of predicting the absorption coefficients of the skin components from the absorption coefficient of the entire skin measured under conditions of variation of its biophysical parameters (the volume concentrations of melanin and blood vessels) over a wide range are evaluated.     

Fluorescence Studies of Melanin by Stepwise Two-Photon Femtosecond Laser Excitation

Fluorescence of synthetic melanin in the solvents H₂O, KOH, ethylene glycol monomethyl ether, and dimethyl sulfoxide has been excited by two-photon absorption at 800 nm, using 120-fs pulses with photon flux densities of 10²⁷ cm^–2.S^–1. Compared to the one-photon (400-nm)-induced fluorescence of melanin, the overall spectral shape is red-shifted and shows a strong environment sensitivity. The decay of the two-photon-induced fluorescence (TPF) of melanin is three-exponential, with a shortest main component of about 200 ps. The results of the TPF studies in line with the unique light absorption property of melanin of a monotonously decreasing absorption spectrum between the near UV-region and the near infrared region indicate that the TPF is realized via stepwise absorption of two 800-nm photons. In comparison to the simultaneous absorption of two photons, the stepwise process needs lower photon flux densities to get a sufficient population of the fluorescent level. This stepwise process offers new possibilities of selective excitation of melanin in skin tissue in a spectral region where there is no overlap with any absorption of another fluorescent tissue component. The first results with different samples of excised human skin tissue (healthy, nevus cell nevi, malignant melanoma) suggest that fluorescence excited in this way yields information on malignant transformation.     

Noninvasive determination of spectral depth of light penetration into skin

A noninvasive method for determining the spectral depth of light penetration into the skin has been developed. It is based on measuring fluxes of radiation reflected from the skin in N _Λ ≥ 3 narrow or wide spectral parts and spectral analysis thereof using the regression approach to solving ill-posed inverse problems. The possibility of estimating the spectral depth of light penetration into skin by skin images in three wide spectral parts (red, green, and blue) is demonstrated. Errors of the method are estimated under conditions of general variability of structural-morphological skin parameters, and its resistance to errors of optical measurements is analyzed.     

血液可见吸收光谱与血氧参数神经网络估算法

总血红蛋白浓度和血氧饱和度是两个基本的血氧参数。文章提出了利用内置双光纤微创探头在位测量大鼠脑组织血氧参数的新方法。首先,利用悬乳液(Intralipid)和全血配置不同总血红蛋白浓度的混合溶液,模拟生物组织模型,用光纤光谱仪测试系统测量组织模型在加氧和去氧时的实时吸收光谱,同时用血氧分析仪(OXI meter)对血氧参数定标,建立测试光谱和定标数据样本集。然后,利用人工神经网络建立血液吸收光谱与血氧参数的神经网络模型,训练后的网络模型能根据吸收光谱输出生物组织的血氧参数值,总血红蛋白浓度和血氧饱和度的平均输出误差分别为±4μmol·L-1和±5%。最后,利用神经网络模型对大鼠脑组织血氧参数进行了在位测试实验,测得脑灰质的血氧饱和度为0.60~0.70,脑白质血氧饱和度为0.45~0.55;总血红蛋白浓度在脑皮层(深度1mm)附近最高,平均110μmol·L-1,其余深度脑组织的总血红蛋白浓度为70~90μmol·L-1。这种方法对脑外科微创手术中实时在位测试脑组织血氧参数具有重要的参考意义。     

A method for the evaluation of the grating envelope in volume holographic media

A novel method for measuring the three-dimensional spatial distribution of gratings in a volume holographic medium is described. In this method, the diffraction of a uniform probe light wave is measured as a function of the deviation (either in angle or wavelength) from the Bragg condition. The envelope function of the grating is obtained by solving the coupled wave equations inversely. Not only the amplitude but also the phase of the envelope function is obtained. This method allows for the depletion of the probe light wave in the hologram and is applicable to both dielectric (refractive index) and absorption gratings. The resolution and the maximum measurable depth in this method are discussed.     

Efficient transfer of light energy to a nanoparticle by means of a resonance atomic lens

A cascade transfer of light energy to a resonance atom situated near a spherical nanoparticle and then, by a nonradiative mechanism, to the nanoparticle itself is considered. It is established that the efficiency of the cascade transfer essentially depends on the frequency and polarization of light, on the distance between the atom and the particle, on the optical properties of the particle, and on the time conditions of radiation. The rate of light absorption by a metal nanoparticle via cascade energy transfer may be 10⁴–10⁵ times higher than the direct absorption of light by a nanoparticle. For a fixed frequency of light, the cascade transfer of energy is a sharply selective function of the distance between the atom and the particle (the resonance width is about 10^?2 of the particle radius). Atomic fluorescence exhibits similar behavior. This feature can form the basis for a new method of optical scanning microscopy and location and localization of atoms near the surface of a particle.     

Light and thermal fields in multilayer skin tissue exposed to laser irradiation

A simple model for calculating the light fields created by a laser beam in a multilayer biological tissue is proposed. On the basis of this model, the coefficient of diffuse reflection of skin and the penetration depth of light are found for the wavelength range 400–850 nm and for a wide range of variation in the structural and optical characteristics of the medium. The effect of localized light absorption by blood vessels is taken into account. The results obtained are shown to agree reasonably with published theoretical and experimental data. Using the found depth distributions of the absorbed energy as source functions for the thermal problem, the analytical solution for the spatiotemporal structure of the temperature field in the cutaneous covering irradiated by a laser beam was obtained. The thermal fields determined in terms of single-and two-layer models are compared, and the corresponding differences are discussed. Examples of the temperature depth profiles obtained at different instants after the beginning of irradiation are presented. The results obtained in terms of the analytical method proposed are demonstrated to agree satisfactorily with those yielded by the numerical finite difference scheme of the solution of the system of heat conduction equations.     

生物组织单光程光谱技术的理论研究

高灵敏度光谱检测技术在临床诊疗和组织光学参数测量中具有极其重要的意义。文章提出了一种差分调制激光光谱技术,将经过生物组织后的散射光与参考光的光程差转换为光谱信号的频率特征,通过相敏检测技术将不同频率的信号进行分离,从而实现生物组织散射光的光程分离。文章分析了差分调制激光光谱的机理及信号的谱特征,并基于文献中的生物组织散射光的光程分布,从理论上讨论了差拍信号的谱特征,即光源调制速率一定时,光谱信号中的主频成分位置只与散射光和参考光的光程差有关;生物组织对光信号的衰减系数会影响光谱信号中频率成分的能量强度分布。分析结果表明,差分调制激光光谱能对生物组织的光谱信号进行光程分离,从而实现生物组织的单光程光谱检测。     

Surface and volume contributions to real and imaginary parts of the heavy-ion optical potential

Starting from the Feshbach expression for the optical potential, explicit formulae for the real and the imaginary parts of the optical potential between two heavy ions (HI's) are obtained. They are each composed of a volume and a surface term. The contributions to the volume term are calculated in two nuclear Fermi liquids which flow through each other starting from the realistic Reid soft core nucleon-nucleon (NN) interaction. Since the Fermi surface is formed by two spheres one obtains a complex Brueckner reaction matrix which is approximated by a complex, effective local interaction. It is used in a fully antisymmetrized double folding procedure to obtain the volume terms of the optical potential between the two HI's. The surface contributions are directly calculated in the collision of the two finite HI's. The collective surface vibrations (3^? octupole state and 2⁺, 4⁺ (T = 0) giant resonances for the ¹⁶O?¹⁶O collision) are included as intermediate states. This yields especially an imaginary contribution at the surface which reduces the transparency found with the volume terms alone. The method is applied to ¹⁶O?¹⁶O scattering at 83 and 332 MeV laboratory energy. The local approximations to the real and imaginary parts obtained in this way agree well with phenomenological fits. The surface terms improve the agreement of the differential cross section at 80 MeV where experimental data are available.