Modeling of optimal conditions for oxyhemoglobin photodissociation in laser-irradiated biotissue

Based on the theory of radiation transfer and a model that describes the structure and optical properties of biotissues, we have found spectral conditions of irradiation of the skin surface that ensure efficient generation of molecular oxygen O₂ in the dermis due to the photodissociation of blood oxyhemoglobin. We show that, for maximal local O₂ formation at depths z ≤ 0.2 mm, 0.2 mm < z ≤ 0.9 mm, 0.9 mm < z ≤ 2.5 mm, and z > 2.5 mm, it is more effective to use wavelengths in the intervals 418 ± 5, 575 ± 5, 585 ± 5, and 600 ± 5 nm, respectively. Physical reasons for the shift of optimal wavelengths toward the red range of the spectrum are described. We show that they are based on the selectivity of optical properties of the skin biotissue, which acts as of a kind of spectral filter the transmission curve of which depends on the depth. It is found that irradiation at a wavelength near 575 nm is optimal for the generation of a maximal amount of O₂ in the intire bulk of the dermis.     

Influence of photon energy on the efficiency of photochemotherapy

It is found that when indotricarbocyanine dye in HeLa cells is exposed to photons with different energies the efficiency of cell damage is wavelength independent provided the photosensitizer absorbs the same number of photons per unit time. In vivo animal experiments with two strains of tumor show that when the wavelength of the irradiating light is increased (668, 740, and 780 nm) and the number of photons absorbed per unit time per unit volume of the tumors is held constant, the damage depth increases by a factor of 1.5 and 3, respectively. The observed changes are related both to differences in the in vivo tissue optical transmission with increasing wavelength and an increased local concentration of oxygen owing to photodissociation of oxyhemoglobin.     

Laser-induced photodissociation of carboxyhemoglobin: An optical method for eliminating the toxic effect of carbon monoxide

We propose and examine an optical method for eliminating the toxic effect of carbon monoxide. The developed method is based on laser-induced photodissociation of carboxyhemoglobin in blood vessels and capillaries. By numerical simulation of the interaction of laser radiation with tissue, we calculate the spectra of the action of carboxyhemoglobin and oxyhemoglobin in cutaneous blood vessels. We show that, despite the sufficiently strong overlap of the action spectra of carboxyhemoglobin and oxyhemoglobin, the substantial difference in the quantum yield values makes it possible to develop an optical method for eliminating the toxic effect of carbon monoxide. We determine the criteria for the efficiency of laser-induced photodissociation of carboxyhemoglobin under direct action on lung alveoli through the skin tissue and intravenously.     

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.     

Laser-induced photodissociation of oxyhemoglobin: Optical method of elimination of hypoxia (oxygen deficiency in biotissue)

We consider the effect of laser-induced in vivo photodissociation of blood oxyhemoglobin on gas exchange in biological tissues. An optical method of laser-induced oxygenation of biotissues is developed and proposed. We show that, in the region of the action of the laser radiation, the degree of oxygenation of a tissue increases. We experimentally confirm that the phenomenon of laser-induced in vivo photodissociation of oxyhemoglobin opens up a new possibility of controlling the local concentration of free molecular oxygen in tissues, eliminating tissue hypoxia, and stimulating aerobic metabolism of cells. We show that the efficiency of the proposed method of laser-induced oxygenation of biotissues proves to be comparable with the efficiency of the hyperbaric oxygenation, but has the advantage of the locality of the action. The proposed optical method of local oxygenation of biotissues will make it possible to eliminate the problem of hypoxia in cancerous tumor tissue and to considerably increase the efficiency of photodynamic, radiation, and chemotherapy in modern oncology.     

A numerical study of radiofrequency deposition in a spherical phantom using surface coils

The electromagnetic fields induced by a surface coil in a spherical phantom, having a wide range of electrical properties, is studied using numerical methods of calculation. The specific absorption rate (SAR), radiofrequency magnetic field (B₁), magnetic field energy within the phantom (E_B), and the volume-averaged SAR (<SAR>) are calculated at 10, 63, and 200 MHz. They are analyzed with respect to dielectric constant, wavelength, and skin depth effects, which become increasingly important in high field magnetic resonance imaging (MRI) where safety and field homogeneity issues need further study. Particular attention is given to solutions representing neural tissue at each frequency. In general, the <SAR> data at high field strengths have local maxima, with a quasi-harmonic behavior, when the following two resonant conditions are satisfied: 1) skin depth becomes comparable to, or larger than, the sample diameter Ds; and 2) Ds is near an integral multiple of the wavelength. These are also the solutions with maximum E_B values and the least homogeneous B₁. Samples undergoing resonance at 200 MHz are shown to have important off-axis B₁ maxima (affecting field homogeneity) and large <SAR> values. Some non-resonating 200-MHz phantoms, including simulations consistent with neural tissue, contain larger SAR maxima than the resonating samples, posing safety concerns in high field imaging of biologic tissue.     

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.     

Effect of temperature on the quantum yield of laser-induced photodissociation of oxyhemoglobin in vivo

We have studied the effect of temperature on laser-induced photodissociation of oxyhemoglobin in vivo by recording the change in the oxygen saturation of arterial blood. We have established that on exposure to low-intensity laser radiation, the local concentration of free oxygen in tissue significantly increases for a body temperature above 40°C, compared with the normal temperature. We demonstrate a unique option for selectively and locally increasing the concentration of free molecular oxygen in tissue, which promotes enhancement of cell metabolism. We consider the possibilities for biomedical use of this phenomenon. The results obtained show that the temperature dependence of the quantum yield for photodissociation of oxyhemoglobin should be considered in development of new therapeutic methods for laser medicine. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 90–93, January–February, 2006.     

Kinetics of oxygenation of skin tissue exposed to low-intensity laser radiation

We present the results of modeling the action spectrum and an experimental investigation of the effect of laser-induced photodissociation of oxyhemoglobin in vivo on the increase in the degree of oxygenation of skin tissue in the exposed area. We have shown that controlling the local concentration of free molecular oxygen in biological tissues together with the possibility of eliminating tissue hypoxia using laser radiation makes it possible to stimulate aerobic cell metabolism and to achieve the needed therapeutic effect. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 120–125, January–February, 2007.     

深度分辨漫反射测量光纤探头设计及特性

漫反射光谱人体成分检测研究中,光纤探头接收漫反射光子穿透深度及传输路径对检测效率及灵敏度影响较大,而传统的检测光纤探头无法实现对特定深度漫反射光子选择性接收。针对人体成分检测需要,提出了采用一定入射-接收角度及半球透镜耦合的漫反射测量光纤探头结构。在三层皮肤模型基础上,结合光纤探头形式改进Monte Carlo程序,计算光纤探头接收漫反射光子穿透深度,有效光子比例,有效信息载荷以及真皮层检测灵敏度。结果表明,设计的光纤探头可实现真皮层漫反射光子选择性接收,检测效率以及测量光谱受非目标层组织结构及光学参数影响较小,可有效提高人体成分无创检测灵敏度。     

Spectrum of the effect of laser radiation on hemoglobin of the blood vessels of skin

We suggested and consider the primary mechanism of biostimulation and of the therapeutic effect of low-level laser radiation caused by a local increase in the effectiveness of oxygen transfer by oxyhemoglobin of the blood vessels of skin. The spectra of the effect of laser radiation on oxyhemoglobin and hemoglobin of the blood vessels of skin are presented which were obtained using a method of numerical simulation with allowance for the optical characteristics of skin and for the depth of penetration into it of radiation of different wavelengths. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 877–860, November–December, 1998.     

The biomedical effect of laser-induced photodissociation of oxyhemoglobin in vivo

It is demonstrated that the photodissociation of oxyhemoglobin in cutaneous blood vessels and capillaries allows additional extraction of molecular oxygen, prevents hypoxia, and stimulates aerobic metabolism of cells. On the basis of the studied phenomena, a new optical technology of local oxygenation of tissue directly in the zone of laser irradiation has been developed. It is shown that the efficiency of the proposed method for laser-induced oxygenation of biotissues is comparable with the efficiency of hyperbaric oxygenation, with local action being an additional advantage. Various aspects of the applications of the new technology in modern medicine in which the elimination of local hypoxia is needed are discussed. The proposed optical method for local oxygenation of biotissues makes it possible to solve the hypoxia problem in malignant tissue and substantially increase the efficiency of photodynamic, radiation, and chemical therapy in modern oncology.     

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。     

Numerical analysis of SOA performance over a wide optical bandwidth in a CO-OFDM transmission system

We present a numerical analysis of the impact of the optical amplification by semiconductor optical amplifiers (SOAs) in a Coherent Optical-Orthogonal Frequency Division Multiplexing transmission link at 100 Gb/s. The numerical modeling of SOA is developed to be able to simulate all of nonlinear effects of the SOA, particularly four-wave mixing effect. This model is integrated into a co-simulation platform to perform a simulation at a system level. Error Vector Magnitude (EVM) measurement is given with respect to the number of subcarriers and phase-amplitude coupling. We show also the dependence of the EVM at the signal wavelength by performing our simulations on a wide optical bandwidth, taking into account the main parameters of the SOA—such as the phase-amplitude coupling factor, the saturation power and the noise figure—that influence the non-linear effects.

     

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.     

Imaging of subcutaneous blood vessels and flow velocity profiles by optical coherence tomography

We have applied a compact low power rapid scanning Doppler Optical Coherence Tomography system to monitor multi-dimensional velocity profiles within the complex vessels and simultaneous real-time non-invasive imaging of skin tissues morphology in vivo, in the wavelength range of 1.3–1.5 nm. Optical clearing of skin tissues has been utilized to achieve depth of OCT images up to 1.7 mm. Current approach enables applying low-power (0.4–0.5 mW) and low-noise broadband near-infrared light sources and obtaining OCT images with down to 12 μm spatial resolution. Two-dimensional time-domain OCT images of complex flow velocity profiles in blood vessel phantom and in vivo subcutaneous human skin tissues are presented. The effect of optical clearing on in vivo images is demonstrated and discussed.     

Ultraviolet Photodissociation of Peptides: New Insight on the Mobile Proton Model

In this work, we study the mechanism of peptide photodissociation by ultraviolet irradiation at 193 nm wavelength and discuss the role of ionization proton in this process. We found that substituting the ionization proton for the alkali metal cations (sodium) in the peptide ions results in significant changes of the photodissociation spectra. The experimental data obtained in this work revealed that the photodissociation process can be described using the mobile proton model introduced earlier for peptide collision dissociation. The results can be used in proteomics research for optimization of mass spectrometer’s parameters to increase the efficiency of peptide dissociation and in developing sequence-specific models for peptide fragmentation prediction.     

Cesium vapor laser with transverse pumping by multiple laser diode arrays

We have demonstrated a Cs vapor laser that utilizes fifteen laser diode arrays for transverse pumping of the gain medium. A maximum output power of 28 W was achieved with a total optical to optical efficiency of 14% and a slope efficiency of 15%. Transverse pumping allows scaling of such a laser system to a higher power level by simple increasing of the gain medium volume and the number of pump sources.     

Non-descanned versus descanned epifluorescence collection in two-photon microscopy: Experiments and Monte Carlo simulations

We report on the design, test and Monte Carlo simulations of a non-descanned (NDS) collection port that we compare to a descanned (DS) port implemented on the same confocal microscope to carry out two-photon excitation fluorescence (TPEF) imaging. Our optical concept provides compactness, a wide field of view to the NDS port and allows the usage of small-area photosensors. The collection efficiency of the NDS port was measured with respect to those of the DS port as function of the imaging depth within a tissue-like optical phantom, for two high numerical aperture objectives. A NDS-to-DS collection ratio as high as about 30 was found for an imaging depth of 500 μm, corresponding to four mean scattering paths of the collected photons within the turbid medium. Measurements were fully interpreted by Monte Carlo simulations of light scattering through the turbid medium and collection by the spatio-angular apertured DS and NDS ports. Comparison of XZ cross-sectional views of mice liver samples imaged with the two ports emphasized the advantage of our NDS device for imaging deeply inside biological samples using TPEF microscopy.     

Soliton pulses generation and filtering using micro-ring resonators for DWDM-based soliton communication

We propose a new optical system that can be used to form the multi-soliton pulses within the micro-ring resonators. The system consists of two micro-ring resonators and an add/drop multiplexer that can be integrated into a single system. The large bandwidth signal is generated by using a soliton pulse propagating in a Kerr-type nonlinear medium. The tuned soliton pulses in either spatial or temporal modes are obtained by using the add/drop multiplexer. Results obtained have shown that the multi-soliton pulses can be localized coherently within the micro-ring waveguide. This is shown that the generation of the multi-soliton pulses within the micro-ring resonator is achieved, which is available for long-distance communication with dense wavelength division multiplexing (DWDM). The significant increase in channel number and spacing are obtained, whereas the large free spectrum range (FSR) of 600 pm is achieved.