Quantification of attenuation and speckle features from endoscopic OCT images for the diagnosis of human brain glioma

Application of optical coherence tomography (OCT) in neurosurgery mostly includes the discrimination between intact and malignant tissues aimed at the detection of brain tumor margins. For particular tissue types, the existing approaches demonstrate low performance, which stimulates the further research for their improvement. The analysis of speckle patterns of brain OCT images is proposed to be taken into account for the discrimination between human brain glioma tissue and intact cortex and white matter. The speckle properties provide additional information of tissue structure, which could help to increase the efficiency of tissue differentiation. The wavelet analysis of OCT speckle patterns was applied to extract the power of local brightness fluctuations in speckle and its standard deviation. The speckle properties are analysed together with attenuation ones using a set of ex vivo brain tissue samples, including glioma of different grades. Various combinations of these features are considered to perform linear discriminant analysis for tissue differentiation. The results reveal that it is reasonable to include the local brightness fluctuations at first two wavelet decomposition levels in the analysis of OCT brain images aimed at neurosurgical diagnosis.

Influence of optical clearing agents on the scattering properties of human nail bed and blood microrheological properties: In vivo and in vitro study

Optical clearing agents (OCAs) are substances that temporarily modify tissue's optical properties, enabling better imaging and light penetration. This study aimed to assess the impact of OCAs on the nail bed and blood using in vivo and in vitro optical methods. In the in vivo part, OCAs were applied to the nail bed, and optical coherence tomography and optical digital capillaroscopy were used to evaluate their effects on optical clearing and capillary blood flow, respectively. In the in vitro part, the collected blood samples were incubated with the OCA and blood aggregation properties were estimated using diffuse light scattering techniques. The results indicate that OCAs significantly influence the optical properties of the nail bed and blood microrheology. These findings suggest that OCAs hold promise for improving optical imaging and diagnostics, particularly for nail bed applications, and can modify blood microrheology.

Optical clearing of human skin: Molecular modeling and in vivo OCT study

The results of in vivo immersion optical clearing of human skin under the action of two different optical clearing agents (OCAs), such as an aqueous sucrose solution and a radiographic contrast agent Omnipaque™ 300 (iohexol), were obtained with the use of optical coherence tomography (OCT) method. The rate of reduction of light scattering coefficient, obtained through an averaged A-scan of the OCT image in the region of dermis within the depths from 350 to 700 μm, were determined to evaluate the efficiency of optical clearing (EOC). The correlations between the EOC and the energy of intermolecular interaction of OCAs with a fragment of collagen peptide have been established as a result of molecular modeling by quantum chemistry methods HF/STO3G/DFT/B3LYP/6-311G(d) of a number of OCAs (glycerol, iohexol, sucrose, ribose, fructose, glucose) with mimetic peptide of collagen (GPH)3 .

Conditions of acceleration and deceleration of the cancer cell growth under osmotic pressure

In this paper, we study a pattern formation in the epidermal layer of skin during tumor development and appearance of a binary surface consisting of healthy and cancer cells forming Turing patterns under external osmotic pressure. The basic methodology of introducing the external influences, for example, time-targeted drug therapy or radiation exposure, influence of electromagnetic fields, laser radiation or other tumor-targeting physical influences act differently in different phases of the cell cycle. In some cases, this can lead to a slowdown in the growth of cancer cells, and sometimes vice versa. Therefore, it is of particular interest to choose the right parameters such as starting time of external pressure, its magnitude and duration depending on the cell cycle of developing cancer cells. We propose a biologically inspired model that allows us to simulate the growth of cancer cells under conditions of osmotic pressure. We divide this growth into two phases. The first is characterized by active cell division, and the second by their growth. In this article, we introduce two types of pressure: short-term and long-term, and looked at what this leads to in different phases. We have found an interesting result, that there are some resonant points in time both in the first and second phases, when the introduction of additional pressure leads to the most significant slowdown in the growth of cancer cells.

Quantitative polarization-sensitive super-resolution solid immersion microscopy reveals biological tissues' birefringence in the terahertz range

Terahertz (THz) technology offers a variety of applications in label-free medical diagnosis and therapy, majority of which rely on the effective medium theory that assumes biological tissues to be optically isotropic and homogeneous at the scale posed by the THz wavelengths. Meanwhile, most recent research discovered mesoscale ([Formula: see text]) heterogeneities of tissues; [Formula: see text] is a wavelength. This posed a problem of studying the related scattering and polarization effects of THz-wave-tissue interactions, while there is still a lack of appropriate tools and instruments for such studies. To address this challenge, in this paper, quantitative polarization-sensitive reflection-mode THz solid immersion (SI) microscope is developed, that comprises a silicon hemisphere-based SI lens, metal-wire-grid polarizer and analyzer, a continuous-wave 0.6 THz ([Formula: see text] µm) backward-wave oscillator (BWO), and a Golay detector. It makes possible the study of local polarization-dependent THz response of mesoscale tissue elements with the resolution as high as [Formula: see text]. It is applied to retrieve the refractive index distributions over the freshly-excised rat brain for the two orthogonal linear polarizations of the THz beam, aimed at uncovering the THz birefringence (structural optical anisotropy) of tissues. The most pronounced birefringence is observed for the Corpus callosum, formed by well-oriented and densely-packed axons bridging the cerebral hemispheres. The observed results are verified by the THz pulsed spectroscopy of the porcine brain, which confirms higher refractive index of the Corpus callosum when the THz beam is polarized along axons. Our findings highlight a potential of the quantitative polarization THz microscopy in biophotonics and medical imaging.

Optical Properties and Fluence Distribution in Rabbit Head Tissues at Selected Laser Wavelengths

The accurate estimation of skin and skull optical properties over a wide wavelength range of laser radiation has great importance in optogenetics and other related applications. In the present work, using the Kubelka-Munk model, finite-element solution of the diffusion equation, inverse adding-doubling (IAD), and Monte-Carlo simulation, we estimated the refractive index, absorption and scattering coefficients, penetration depth, and the optical fluence distribution in rabbit head tissues ex vivo, after dividing the heads into three types of tissues with an average thickness of skin of 1.1 mm, skull of 1 mm, and brain of 3 mm. The total diffuse reflectance and transmittance were measured using a single integrating sphere optical setup for laser radiation of 532, 660, 785, and 980 nm. The calculated optical properties were then applied to the diffusion equation to compute the optical fluence rate distribution at the boundary of the samples using the finite element method. Monte-Carlo simulation was implemented for estimating the optical fluence distribution through a model containing the three tissue layers. The scattering coefficient decreased at longer wavelengths, leading to an increase in optical fluence inside the tissue samples, indicating a higher penetration depth, especially at 980 nm. In general, the obtained results show good agreement with relevant literature.

Terahertz dielectric spectroscopy and solid immersion microscopy of ex vivo glioma model 101.8: brain tissue heterogeneity

Terahertz (THz) technology holds strong potential for the intraoperative label-free diagnosis of brain gliomas, aimed at ensuring their gross-total resection. Nevertheless, it is still far from clinical applications due to the limited knowledge about the THz-wave-brain tissue interactions. In this work, rat glioma model 101.8 was studied ex vivo using both the THz pulsed spectroscopy and the 0.15λ-resolution THz solid immersion microscopy (λ is a free-space wavelength). The considered homograft model mimics glioblastoma, possesses heterogeneous character, unclear margins, and microvascularity. Using the THz spectroscopy, effective THz optical properties of brain tissues were studied, as averaged within the diffraction-limited beam spot. Thus measured THz optical properties revealed a persistent difference between intact tissues and a tumor, along with fluctuations of the tissue response over the rat brain. The observed THz microscopic images showed heterogeneous character of brain tissues at the scale posed by the THz wavelengths, which is due to the distinct response of white and gray matters, the presence of different neurovascular structures, as well as due to the necrotic debris and hemorrhage in a tumor. Such heterogeneities might significantly complicate delineation of tumor margins during the intraoperative THz neurodiagnosis. The presented results for the first time pose the problem of studying the inhomogeneity of brain tissues that causes scattering of THz waves, as well as the urgent need to use the radiation transfer theory for describing the THz-wave - tissue interactions.

Terahertz dielectric spectroscopy of human brain gliomas and intact tissues ex vivo: double-Debye and double-overdamped-oscillator models of dielectric response

Terahertz (THz) technology offers novel opportunities in the intraoperative neurodiagnosis. Recently, the significant progress was achieved in the study of brain gliomas and intact tissues, highlighting a potential for THz technology in the intraoperative delineation of tumor margins. However, a lack of physical models describing the THz dielectric permittivity of healthy and pathological brain tissues restrains the further progress in this field. In the present work, the ex vivo THz dielectric response of human brain tissues was analyzed using relaxation models of complex dielectric permittivity. Dielectric response of tissues was parametrized by a pair of the Debye relaxators and a pair of the overdamped-oscillators - namely, the double-Debye (DD) and double-overdamped-oscillator (DO) models. Both models accurately reproduce the experimental curves for the intact tissues and the WHO Grades I-IV gliomas. While the DD model is more common for THz biophotonics, the DO model is more physically rigorous, since it satisfies the sum rule. In this way, the DO model and the sum rule were, then, applied to estimate the content of water in intact tissues and gliomas ex vivo. The observed results agreed well with the earlier-reported data, justifying water as a main endogenous label of brain tumors in the THz range. The developed models can be used to describe completely the THz-wave - human brain tissues interactions in the frameworks of classical electrodynamics, being quite important for further research and developments in THz neurodiagnosis of tumors.

Methods for Optical Skin Clearing in Molecular Optical Imaging in Dermatology

This short review describes recent progress in using optical clearing (OC) technique in skin studies. Optical clearing is an efficient tool for enhancing the probing depth and data quality in multiphoton microscopy and Raman spectroscopy. Here, we discuss the main mechanisms of OC, its safety, advantages, and limitations. The data on the OC effect on the skin water content are presented. It was demonstrated that 70% glycerol and 100% Omnipaque^TM 300 reduce the water content in the skin. Both OC agents (OCAs) significantly affect the strongly bound and weakly bound water. However, Omnipaque^TM 300 causes considerably less skin dehydration than glycerol. In addition, the results of examination of the OC effect on autofluorescence in two-photon excitation and background fluorescence in Raman scattering at different skin depths are presented. It is shown that Omnipaque^TM 300 is a promising OCA due to its ability to reduce background fluorescence in the upper skin layers. The possibility of multimodal imaging combining optical methods and OC technique is discussed.

Multimodal Optical Diagnostics of Glycated Biological Tissues

Diabetes mellitus is a metabolic disorder characterized by chronic hyperglycemia accompanied by the disruption of carbohydrate, lipid, and proteins metabolism and development of long-term microvascular, macrovascular, and neuropathic changes. This review presents the results of spectroscopic studies on the glycation of tissues and cell proteins in organisms with naturally developing and model diabetes and in vitro glycated samples in a wide range of electromagnetic waves, from visible light to terahertz radiation. Experiments on the refractometric measurements of glycated and oxygenated hemoglobin in broad wavelength and temperature ranges using digital holographic microscopy and diffraction tomography are discussed, as well as possible application of these methods in the diabetes diagnostics. It is shown that the development and implementation of multimodal approaches based on a combination of phase diagnostics with other methods is another promising direction in the diabetes diagnostics. The possibilities of using optical clearing agents for monitoring the diffusion of substances in the glycated tissues and blood flow dynamics in the pancreas of animals with induced diabetes have also been analyzed.

Recent progress in tissue optical clearing for spectroscopic application

This paper aims to review recent progress in optical clearing of the skin and over naturally turbid biological tissues and blood using this technique in vivo and in vitro with multiphoton microscopy, confocal Raman microscopy, confocal microscopy, NIR spectroscopy, optical coherence tomography, and laser speckle contrast imaging. Basic principles of the technique, its safety, advantages and limitations are discussed. The application of optical clearing agent on a tissue allows for controlling the optical properties of tissue. Optical clearing-induced reduction of tissue scattering significantly facilitates the observation of deep-located tissue regions, at the same time improving the resolution and image contrast for a variety of optical imaging methods suitable for clinical applications, such as diagnostics and laser treatment of skin diseases, mucosal tumor imaging, laser disruption of pathological abnormalities, etc.

Glycerol dehydration of native and diabetic animal tissues studied by THz-TDS and NMR methods

The optical clearing method has been widely used for different spectral ranges where it provides tissue transparency. In this work, we observed the enhanced penetration of the terahertz waves inside biological samples (skin, kidney, and cornea) treated with glycerol solutions inducing changes of optical and dielectric properties. It was supported by the observed trend of free-to-bound water ratio measured by the nuclear magnetic resonance (NMR) method. The terahertz clearing efficiency was found to be less for diabetic samples than for normal ones. Results of the numerical simulation proved that pulse deformation is due to bigger penetration depth caused by the reduction of absorption and refraction at optical clearing.

Multiresolution analysis of pathological changes in cerebral venous dynamics in newborn mice with intracranial hemorrhage: adrenorelated vasorelaxation

Intracranial hemorrhage (ICH) is the major problem of modern neonatal intensive care. Abnormalities of cerebral venous blood flow (CVBF) can play a crucial role in the development of ICH in infants. The mechanisms underlying these pathological processes remain unclear; however it has been established that the activation of the adrenorelated vasorelaxation can be an important reason. Aiming to reach a better understanding of how the adrenodependent relaxation of cerebral veins contributes to the development of ICH in newborns, we study here the effects of pharmacological stimulation of adrenorelated dilation of the sagittal sinus by isoproterenol on the cerebral venous hemodynamics. Our study is performed in newborn mice at different stages of ICH using the laser speckle contrast imaging and wavelet analysis of the vascular dynamics of CVBF. We show that the dilation of the sagittal sinus with the decreased velocity of blood flow presides to the stress-induced ICH in newborn mice. These morphofunctional vascular changes are accompanied by an increased variance of the wavelet-coefficients in the areas of endothelial and non-endothelial (KATP-channels activity of vascular muscle) sympathetic components of the CVBF variability. Changes in the cerebral venous hemodynamics at the latent stage of ICH are associated with a high responsiveness of the sagittal sinus to isoproterenol quantifying by wavelet-coefficients related to a very slow region of the frequency domain. The obtained results certify that a high activation of the adrenergic-related vasodilatory responses to severe stress in newborn mice can be one of the important mechanisms underlying the development of ICH. Thus, the venous insufficiency with the decreased blood outflow from the brain associated with changes in the endothelial and the sympathetic components of CVBF-variability can be treated as prognostic criteria for the risk of ICH during the first days after birth.

[Kinetics of changes in the coefficient of transmission of the adipose tissue in vitro as a result of photodynamic action]

Changes in the light transmission coefficient of human adipose cells as a result of photodynamic action have been detected and investigated. Based on the statistical processing of digital micrographs of thin tissue slices, the kinetics of processes occurring in the adipose tissue has been quantitatively estimated. It has been suggested that the effects observed are brought about through the lipolysis of adipose cells with the retention of their structure.

[Photodynamic effect on cells of human adipose tissue in vitro]

Changes in optical properties of human adipose tissue cells after photodynamic exposure in vitro were found and investigated. Analysis of the kinetics of the process was realized by means of photomicrography of the object investigated. The statistical computer processing of digital photos obtained gave us an opportunity to estimate quantitatively the kinetics of photodynamic effect upon the tissue. Optical interpretation of the photos obtained indicates that the observed phenomenon corresponds to the partial lysis of adipose tissue cells without their complete destruction.

[Diffusion of methylene blue in the human maxillary sinus mucosa]

The coefficient of diffusion of methylene blue in pathologically changed human maxillary sinus mucosa in vitro has been estimated for the first time. The mean value of the diffusion coefficient is (4.8 +/- 2.9) x 10(-7) cm2/s. The method is based on the registration of the dynamics of reflectance of tissue samples under the action of the dye. The diffusion coefficient has been estimated by approximation of experimental data in the framework of the model presented.

[Plasma dehydratation self-organization in patients with coronary heart]

The functional morphology of biological fluids is a basically new branch of science, which is based on the study of a result of phase change processes in the substrate under study. The paper shows the specific features of plasma spatial organization in patients with chronic and acute coronary heart disease (CHD). The findings may be used as an additional criterion for the differential diagnosis of the above forms of CHD and open up a new line in the diagnosis and risk stratification in CHD patients.

Optical monitoring of microlymphatic disturbances during experimental lymphedema

BACKGROUND

Rat mesentery has been widely used to study microvascular functions. The goal of this work is to extend this animal model to monitor blood and lymph microvessel function during lymphedema.

METHODS AND RESULTS

Lymphedema is created by microsurgical removal of regional lymph nodes (lymphadenectomy) or ligation of the collecting vein. Water volume in mesenteric tissue, microvessel diameters, phasic contraction, valve function, lymph flow velocity, and cell migration were analyzed during lymphedema development. Dynamic observation of water amount after lymphadenectomy revealed increasing edema from 30 min to 1 week; greatest degree of edema at one week, and gradual decrease in edema from 1 to 11 weeks. These effects were accompanied by acute constriction of lymph vessels and slowing of lymph flow velocity, switching to dilation and appearance of new blood capillaries at week 1, progressing to dilation and degenerative changes of the microlymphatic wall at week 4, and, finally, leading to lymphatic fibrosis and lymphangiogenesis at week 11. Acute venous insufficiency (30 min after vein ligation) led to significant edema, decreasing blood flow velocity to stasis, and output of erythrocytes from venules to interstitium, with further movement to microlymphatics and regional lymph nodes.

CONCLUSIONS

Rat mesentery as an animal model in combination with an advanced optical imaging system is valuable in studying microlymphatic disturbances in mesentery during the development of experimental lymphedema from latent period to chronic stages, including monitoring of individual cell dislocation with high resolution optical imaging.

[Role of the carbohydrate-binding center of bacterial lectin in the effect on adipocytes under the influence of increased temperature]

The effect of temperature and lectin from bacteria of the genues Azospirillum with blocked activity on human adipose tissue cells has been studied. The temperature used was 43.5 +/- 0.5 degrees C. Comparative results are given for the effect of lectin with the blocked and active carbohydrate-binding centers on adipocytes during heating, and the time course of the structural changes of adipocytes is described. When lectin with the active carbohydrate-binding centers was used for treatment, the heat-treated cells of a healthy obesity-prone subject died on the average in 55 +/- 5 min, whereas cells treated with lectin with the L-fucose-blocked carbohydrate-binding centers died in 80 +/- 5 min. The heat-treated cells of a diabetic obesity-prone patient died in 150 +/- 10 min on average when exposed to both active and inactive lectin. Consequently, when the lectin center is blocked with L-fucose, the effectiveness of lectin action on adipose cells of healthy obesity-prone persons decreases.

Optical clearing of skin using flashlamp-induced enhancement of epidermal permeability

BACKGROUND AND OBJECTIVES

Strong light scattering in skin prevents precise targeting of optical energy in therapeutic and diagnostic applications. Optical immersion based on matching refractive index of scattering centers with that of surrounding matter through introduction of an exogenous index-matching agent can alleviate the problem. However, slow diffusion of the index-matching agent through skin barrier makes practical implementation of this approach difficult. We propose a method of accelerating penetration of the index-matching compounds by enhancing skin permeability through creating a lattice of micro-zones (islets) of limited thermal damage in the stratum corneum (SC).

STUDY DESIGN/MATERIALS AND METHODS

A flash lamp (intense pulsed light) system and an island mask with a pattern of absorbing centers (center size approximately 75-120 microm, lattice pitch approximately 450-500 microm) were used to create the lattice of islets of damage (LID). Index-matching agents, such as glucose solution, propylene glycol solution, and glycerol solution, were applied.

RESULTS

Experimental results of optical clearing ex vivo rat and pig skin, and ex vivo and in vivo human skin are presented. Optical transmission spectra of the skin samples with LID were measured during some 2 hours after application of index-matching chemical agents. In order to assess and compare the clearing rate under different treatment and clearing agents we calculated the quantity that we call "relative transmittance": T(rel) = I(t)(lambda)/I(0)(lambda), were I(t)(lambda) is the intensity measured at elapsed time t. The dynamics of relative transmittance of skin samples at 470 and 650 nm shows that the implementation of limited thermal damage technique leads to a 3-10-fold increase of optical clearing (rise of transmittance) rate compared to the results obtained when the samples were treated with high-intensity light pulses but without the use of island damage mask (IDM). It was observed from the plotted spectra of relative transmittance that the maximum increase of transmitted light intensity has been obtained with glucose solution as a clearing agent. Noteworthy is the difference in the trend of spectral curves: relative transmittance spectrum for glycerol reveals, on the whole, a greater slope which may be indicative of higher extent of index matching between the scattering centers and base material for this index-matching agent. Under the transillumination of the skin sample by the wide flat beam the more effective clearing (the increase of transmitted intensity) is attained within the hemoglobin absorption bands; with the narrow quasi-collimated beam the higher relative transmittance was observed over the intervals of minimum absorption.

CONCLUSIONS

The use of specially designed island mask combined with non-laser intensive pulse irradiation produces a lattice of islands of limited thermal damage in SC that substantially enhances the penetration rate of topically applied index-matching agents. The suggested technique gave comparable magnitudes of clearing dynamics enhancement for glucose solution, glycerol solution, and propylene glycol solution applied to mammalian skin.

Design and evaluation of a novel portable erythema-melanin-meter

BACKGROUND AND OBJECTIVES

Objective evaluation of the pigmentation index (PI) and the eythema index (EI) of human skin is a prerequisite for successful optimization of laser- and intense-pulsed-light (IPL)-based treatment modalities in dermatology.

STUDY DESIGN/MATERIALS AND METHODS

We describe a three-wavelength technique for determining PI and EI as well as its particular implementation using LEDs operating at wavelengths of 560, 650, and 710 nm and a large-area photodiode. The instrument has been evaluated both in vitro and in vivo.

RESULTS

In vitro, good correlation between the measured indices and results obtained with commercially available techniques has been observed. In addition, linearity of the PI with melanin concentration in the phantom medium up to 7 x 10(-3) nm(-1) (defined as a slope of the optical density spectrum) has been established. In vivo, feasibility of using the technique for predicting the minimal erythema dose (MED), minimal phototoxic dose (MPD), and the threshold of epidermal damage in a photothermal treatment has been demonstrated.

CONCLUSIONS

The data suggest that the technique has a substantial potential as a method of pre-treatment diagnostics for photochemical and photothermal procedures.

[Effect of high concentrations of glucose on physiological parameters of platelets in patients with ischemic heart disease.]

Analysis of functional state of the erythrocyte system was carried out in 45 patients with stable class II and III angina including those with concomitant non insulin dependent diabetes and in 15 practically healthy subjects. The analysis was made in the process of upsetting the balance of the erythrocyte system by incubation with high concentrations of glucose in vitro. Functional state of erythrocytes was assessed by construction of fragments of a phase portrait on a plane representing relationship between dimensions of erythrocytes, glucose concentration and rate of the above mentioned process.

[Determination of glucose diffusion coefficient in the human eye sclera]

The diffusion coefficients of aqueous glucose solutions in human sclera in vitro were estimated. The method is based on measurements of time-dependence of collimated transmittance of scleral samples under the action of biocompatible immersion liquids. It was shown that changes in collimated transmittance are connected with the matching between the indices of refraction of scleral scatterers and interstitial fluid. The dynamics of interstitial fluid replacement was registered by recording successively the collimated transmittance spectra in the range of 400-800 nm. For a quantitative description of the replacement process, a diffusion model was proposed, which assumes that the diffusion coefficient is constant throughout the volume of the scleral sample. Experimental results for glucose solutions of concentrations 0.18, 0.3, and 0.4 g/ml are presented. The diffusion coefficients were estimated by approximating the experimental data in the framework of the proposed model.

Investigation of blood flow microcirculation by diffusing wave spectroscopy

This article presents a technique and a setup for noninvasive in vivo studies of cutaneous microcirculation. The technique is based on the analysis of intensity fluctuations of scattered coherent light. The analysis is made in terms of diffusing wave spectroscopy. The developed technique can be used in clinical practice to determine the motion pattern of scattering particles (such as red blood cells) in randomly inhomogeneous media (such as biological tissues). The average size of scattering particles can be comparable to the wavelength of scattered radiation.

Experimental evaluation on the transmission optical microscopy for the diagnosis of lymphedema

The mechanisms of disturbance of lymph microcirculation during development postmastectomy lymphedema (PML) are little known. The study of these mechanisms on human subjects has many difficulties: time of clinical onset of PML is indefinite and unpredictable and the methods for imaging of microlymphatics are limited. The advantages of the optical methods, especially, light microscopy are the high quality of lymphocytes dynamic imaging, possibility of the determination of absolute lymph flow velocity in a wide range, capability for simultaneous registration of blood microvessel function around lymphatics. The experimental lymphedema is created on rat mesentery by ligation of the collecting vein. It was found that after such ligation edema was clearly developed, and microcirculation was significantly disturbed including reduction of lymph flow velocity, constriction of lymphatics, inhibition of phasic activity on the background of pathological increasing of blood vessels permeability and stasis of blood flow.

Enhance light penetration in tissue for high resolution optical imaging techniques by the use of biocompatible chemical agents

The highly scattering nature of human tissue limits light penetration depth in the near infrared range, which prevents the deeper microstructures from imaging. In order to enhance the imaging depth for the current high resolution optical imaging techniques, the light scattering in tissue must be reduced. This paper demonstrates that the light scattering of tissue can be effectively reduced by the topical applications of the biocompatible chemical agents. In this study the propylene glycol and glucose solutions were chosen for the demonstrations through topical applications and intra-dermis injection, respectively. The experiments were performed in vitro and in vivo by the use of the optical coherence tomography system. The results clearly show that the OCT imaging depth and contrast are dramatically improved after the topical applications of propylene glycol solution. Such improvement was discussed on the basis of refractive index matching environment created by the chemical agents, which effectively reduces the light scattering of tissue. Rayleigh-Gans approximation of light scattering was also used to show theoretically how the increase of refractive index of background medium would have effect on the reduced scattering coefficient of tissue. The theoretical and experimental results were qualitatively consistent.

[Functional organization of lymphatic microvessels of the rat mesentery]

Lymph flow as measured with biomicroscopic and speckle-interferometrical techniques was very unstable and its rate did not depend on lymphangion diameter in the rat mesentery. A correlation was found between amount of cells in the lymph flow and other indices of lymphangion functions. All microvessels with phasic contractions and/or working valve were revealed as having a lymph flow. The phasic activity and the valve work correlated with each other. The higher the amplitude and frequency of the phasic activity and the longer the contraction cycle, the higher was the rate of the valve work.

Use of low-coherence speckled speckles for bioflow measurements

Formation of speckled speckles in the case of biflow perfusion by partially coherent light was considered. Dependencies of statistical characteristics of low-coherence biospeckles with a small number of scatterers on the scattering properties of the flow and on the coherence length of incident light were analyzed. It was shown that the value of the Doppler bandwidth in the scattered light essentially depends on the ratio between the coherence length and the average size of the flow's inhomogeneities. A procedure for reconstructing velocity distribution in a single blood vessel was suggested.

Coherent optical techniques for the analysis of tissue structure and dynamics

This paper summarizes the description of the speckle-correlation, speckle-interferometric, and polarimetric methods and instruments designed for various tissue structure imaging and their optical and dynamical parameter monitoring. © 1999 Society of Photo-Optical Instrumentation Engineers.

Guest editorial: special section on coherence domain optical methods in biomedical science and clinics

This Special Section Guest Editorial provides an overview of the topical area and an introduction to the articles featured in the special section.

Characteristic scales of optical field depolarization and decorrelation for multiple scattering media and tissues

Decorrelation and depolarization properties of multiply scattering media and tissues in the case of propagation of coherent probe beams are analyzed in terms of photon path distribution. A specific correlation time determining the relationship between correlation and polarization states of scattered optical fields is introduced. Results of correlation and polarization experiments with phantom scatterers (such as water suspensions of polystyrene spheres) and tissues with controlled optical properties (such as the human sclera) are presented. © 1999 Society of Photo-Optical Instrumentation Engineers.

Guest Editorial: Special Section on Interferometry in Biomedicine, Part II

This Special Section Guest Editorial provides an overview of the topical area and an introduction to the articles featured in the special section.

Guest editorial: special section on interferometry in biomedicine, part I

This Special Section Guest Editorial provides an overview of the topical area and an introduction to the articles featured in the special section.

[Water exchange in human crystalline lens studied by combined dispersion confocal microspectroscopy]

We have employed the technique of the confocal Raman microspectroscopy to monitor water exchange in human eye lens in vitro. Heavy water (D2O) was used as a marker of the exchange. Raman spectra in the high frequency range (2200-3500 cm-1) were successively recorded at several locations inside the lens in order to register dynamics of the replacement of H2O by D2O. The intensities of the Raman peaks at 2450 cm-1 (OD stretch) and 3390 cm-1 (OH stretch) were used as indicators of H2O/D2O exchange, whereas the Raman peak at 2935 cm-1 (CH stretch of protein) served as an internal standard. The ratios of the Raman intensities I2450/I2935 and I3390/I2935 determined the relative concentrations of D2O and H2O, respectively. For the quantitative description of the exchange, we proposed a diffusion model assuming a constant diffusion coefficient over the volume of the lens. We report the results of experiments performed on four fresh and one fixed lenses. The diffusion coefficient of D2O in the human eye lens was estimated using the least-squares fit of the experimental data.

Effect of the scattering delay on time-dependent photon migration in turbid media

We modified the diffusion approximation of the time-dependent radiative transfer equation to account for a finite scattering delay time. Under the usual assumptions of the diffusion approximation, the effect of the scattering delay leads to a simple renormalization of the light velocity that appears in the diffusion equation. Accuracy of the model was evaluated by comparison with Monte Carlo simulations in the frequency domain for a semi-infinite geometry. A good agreement is demonstrated for both matched and mismatched boundary conditions when the distance from the source is sufficiently large. The modified diffusion model predicts that the neglect of the scattering delay when the optical properties of the turbid material are derived from normalized frequency- or time-domain measurements should result in an underestimation of the absorption coefficient and an overestimation of the transport coefficient. These observations are consistent with the published experimental data.

Spatial speckle correlometry in applications to tissue structure monitoring

Asymptotic behavior of temporal autocorrelation functions of speckle intensity fluctuations induced by tissue scanning with a focused probe beam is experimentally studied for the transition from a single-scattering to a multiple-scattering mode. Such parameters as the exponential factor (or the Hurst coefficient) and the Hausdo dimension are proposed for the characterization and the visualization of the variations of the studied tissues' optical properties in generalized form. We studied reversible transition between various scattering modes stimulated by the application of certain chemical agents to the human sclera samples using speckle intensity correlation analysis; corresponding results are presented. The possibilities of the scattering structures imaging with local estimations of the exponential factor of speckle intensity fluctuations are shown in in vitro experiments with samples of human skin epidermis.

Fractality of speckle intensity fluctuations

Coherent-light diffraction on random phase screens with fractal properties leads to the formation of speckle patterns with peculiarities in correlation characteristics in the small-scale region. Such peculiarities are manifested in asymptotic behavior in intensity autocorrelation and structure functions in the vicinity of the zero values of their arguments. Intensity fluctuations in the far and the near diffraction zones are also characterized by values of fractal (Hausdorff-Besicovitch) dimensions D(HB), differing from the corresponding Euclidean dimension. Relationships between the exponential factors of the structure functions of boundary field phase and scattered-light intensity fluctuations as well as between values of D(HB) have been obtained as a result of speckle-formation analysis for different conditions. Their dependencies on the illumination and observation conditions obtained in experiments with fractallike scatterers (rough glass plates) are in satisfactory agreement with theoretical results.

Laser light scattering in biomedical diagnostics and therapy

The description of special features of laser light interaction with biotissues, such as the skin, eye and dental tissues etc., with respect to laser diagnostics and therapy methods development is done. Optical models of transparent and turbid biotissues are analyzed. The role of static and dynamic light scattering in the light dosimetry, tissue heating, and receiving information of biotissue optical parameters, its structure, movements, and vibrations is considered.