We use heterodyne detection to characterize the Wigner phase space distribution W(x,p) of an optical field in position x and momentum p. Using a low coherence source, this method is used to obtain optical phase space distributions for various photon path lengths in a multiple scattering medium. These techniques may find important applications in analyzing and enhancing images obtained in coherence tomography as well as in characterizing low coherence sources.

The angle biased Monte Carlo technique is applied to simulate the OCT signal from homogeneous turbid medium. The OCT signal is divided into two categories: one is from a specific imaging target layer in the turbid medium; the other is from the other background medium. The Class II signal has wider spatial and angular distribution than the Class I signal. And it experiences more scattering events. The multiple scattered photons will decrease the contrast of the OCT image and their contributions become dominant at larger depths. The average number of scattering events increases with the probing depth for both Class I and II lights. Experimental study is conducted by measuring the depth-resolved degree of polarization (DOP) of the back- scattered signal from the turbid media. The DOP is derived form the Stokes vector measurements. The incident light is linear polarized and could be depolarize by the multiple scattering. The DOP decreases to 0.5 when Class I signal is equal to the Class II signal. Experiments in the intralipid solution with different scattering coefficient show the imaging depth is limited to 3-4 optical depths.

Optical coherence tomography (OCT) is a new noninvasive tomographic imaging techniques with resolution of micron scale. It has high potential for the application in many fields such as medicine, biology, material and so no. In this paper, our OCT system is shown to be successful in the study of both botanic and creatural tissue imaging. Furthermore we also use the Monte-Carlo simulation method to analyze 2D OCT image. The differences between single scattered light and multiply scattered light and also its influence on the quality of OCT image are discussed. To show an example, a conduit immersing in a high scattering medium as the model of blood vessel is simulated and the theoretical result is directly shown in the form of image. The conduit immersing in the high scattering medium can be clearly seen in the imags. Comparing with the experimental image they are basically accordant. Some results helpful for experimental research area draw through the simulation. To further enhance the resolution of OCT imaging, computer processing and image deconvolution are introduced. The depth resolution is improved by more than one order for the sample image and thus enables intracellular imaging.

Optical coherence tomography (OCT) affords diffraction- limited resolution to a depth of several hundred micrometers is tissue while diffuse optical tomography (DOT) offers few millimeter resolution through several centimeters of tissue. OCT typically works with singly scattered light while DOT uses diffuse light. To the best of our knowledge, no imaging technique uses light that has scattered multiple times, but is not yet diffuse. We believe that such a technique can offer hundred micron resolution for image depths up to a centimeter in tissue, thus filling the void between OCT and DOT. We demonstrate how OCT and DOT can be extended to the few scattering regime. We present experimental measurements of the broadening of the OCT point spread function as the imaging volume is moved to greater optical depth sin a highly scattering medium. Comparisons to Monte Carlo simulations are made in our other manuscript in this proceedings.

Optical coherence tomography (OCT) systems normally operate in regions of the near-IR spectrum in which absorption losses are small compared to scattering losses. We have been exploring the concept of absorption imaging with OCT using a pair of sources that emit on either side of an edge of a strong absorption band of water. In this report a method is introduced for measurement of differential absorption that is based on Fourier transformation of partially coherent interference signals. In experiments designed to test the feasibility of the method, we measured local water concentrations in tissue phantoms and the hydrated epidermis of living skin using a specially configured interferometer illuminated by LEDs that emit in bands centered on 1310 nm and 1460 nm. The results show that absorption losses can be measured in spite of inherent noise form backscattering variations and speckle, but the need for signal averaging places a lower limit on the sampling volume. New inversion algorithms for true tomographic imaging are under development that take advantage of the multiple projections of a scanned conical beam.

The goal of OCT elastography is to quantify microscope strain induced inside a tissue by stress applied externally. Images of internal strain or displacement may provide valuable information about pathological processes such as edema and fibrosis which are known to alter the mechanical properties of tissue.In this sty we developed experimental methods for measuring internal deformation in highly scattering tissue with OCT and applied them to tissue phantoms and living tissue. Piezoelectric actuators were configured to compress the samples in steps of 5-10 micrometers as images were captured synchronously using either a frame or a line-by-line acquisition mode. The displacements of structures inside the samples were quantified using speckle- tracking algorithms based on cross correlation or optical flow of selected features. Displacements as small as a few micrometers were measurable in heterogeneous gelatin phantoms containing scattering particles and living skin. The rules suggest that the composition of tissue layers whose elasticities differ greatly can be deduced visually from image sequences without the need for complicated image processing. However, better models are needed to transform the displacement images into quantitative maps of subtle regional variations of the elastic modulus.

We present an all-fiber, compact device for optical frequency-domain reflectometry. The device combines a Michelson interferometer with a fiber Fabry-Perot tunable filter for rapid wavelength scanning. The free spectral range of the filter is 32 nm and scans may be complete in less than 2.5 ms. Images of the surface geometry of the material under study can be reconstructed at scan rates up to 400 Hz with an axial resolution of 20 micrometers .

Different compatibility criteria are discussed for the simultaneous presentation of OCT transversal and confocal images from the retina, in a stand-alone OCT/confocal imaging system.

Burn depth assessment is a key step guiding the treatment plan in patients who have sustained thermal injuries. We have developed a technique, polarization sensitive optical coherence tomography (PS-OCT), to provide the physician with a quantitative estimate of actual burn depth. We generated burns of various depths by contacting rates with a brass rod preheated to 75 degrees for 5, 15, or 30 seconds. PS-OCT imags birefringence in biological tissue, through the depth resolved changes in the polarization state of light propagated and reflected from the sample. Preliminary result are presented that show a correlation between the loss of birefringence due to thermal injury and the actual burn depth determined by histological analysis. PS-OCT is a noninvasive technique which potentially can give physicians the accuracy to formulate the best treatment plan for burn patients.

A technology capable of imaging tissue, at or near the cellular level, could lead to the detection of neoplasias at earlier stages than currently possible. This could significantly improve patient outcomes, since once cancer becomes metastatic, cure is difficult. Optical coherence tomography (OCT), a recently developed imaging technology, has ben shown to achieve resolution in the cellular and subcellular range, and it could improve the diagnostic range of clinical imaging procedures. To assess the clinical applicability of OCT, neoplastic specimens from the urinary, gastrointestinal and female reproductive tract were imaged. Sharp differentiation of structures included the mucosa/submucosal/muscularis boundaries, epithelium, glands, supportive tissue, and intramural cysts. The ability of optical coherence tomography to image tissue microstructure at or near the cellular level make it a potentially powerful technology for minimally invasive assessment of tissue microstructure. The resolution of optical coherence tomography, which is greater than any current clinical imaging modality, make it particularly attractive for the assessment of early neoplastic changes.

Based on results of clinical examination of about 200 patients we discuss capabilities of the optical coherence tomography (OCT) in monitoring and diagnosing of various pathophysiological processes. Performed in several clinical areas including dermatology, urology, laryngology, gynecology, and dentistry, our study shows the existence of common optical features in manifestation of a pathophysiological process in different organs. In this paper we focus at such universal tomographic optical signs for processes of inflammation, necrosis and tumor growth. We also present data on dynamical OCT monitoring of evolution of pathophysiological processes, both at the stage of disease development and following-up results of different treatments such as drug application, radiation therapy, cryodestruction, and laser vaporization. The discovered peculiarities of OCT images for structural and functional imaging of biological tissues can be put as a basis for application of this method for diagnosing of pathology, guidance of treatment, estimation of its adequacy and assessing of the healing process.

Polarization and correlation techniques of tissue structure visualization as well as 'direct' imaging by means of analysis of spatial distributions of the scattered light intensity are discussed by using the concept of statistics of effective optical paths. Monte Carlo simulation has allowed us to study the quality of the reconstructed imags for different schemes of image reconstruction. Absorbing half-plane embedded in the isotropic scattering slab has been used as a model inhomogeneity. Potentialities of relatively simple imaging techniques based on the application of continuous-wave laser sources are discussed.

The refractive index matching of components of highly scattering tissue has a strong influence on its transmittance and reflectance what can be considered as a new tool for imaging within relatively thick tissues. We present experimental data on various solutions, gels and oils influence on optical properties of in vivo human eye and in vivo human skin. The dynamics of tissue optical properties depending on matter diffusion rate within tissue is studied. The possible application of refractive index matching effect for diffusing-photon imaging is discussed.

Changes in the ultrastructure of vascular tissue due to pathologies such as atherosclerosis may be manifested as subtle changes in the mechanical properties of the arterial wall. The ability to detect these changes is considered to be important in the early diagnosis of atherosclerosis. In order to evaluate the subtle viscoelastic properties of the arterial wall, a highly sensitive means of evaluating mechanical strain in the tissue is required. Herein we will present a novel laser speckle strain gauge for evaluating mechanical microstrains in perfused and superfused vessel segments. The strain gauge relies upon 2D frequency transforms of stacked speckle histories, which are time sequences of one dimensional views of the backscattered light stacked into a 2D array such that time is along the vertical axis and space is along the horizontal axis. The gauge can be made sensitive only to in-plane strains. Sensitivity of the gauge is on the order of single microstrain. By mechanically straining the vessel segments in a custom microtensile testing machine fitted with a high sensitivity load cell, mechanical constants of the vessel wall can be derived and changes in the mechanical behavior due to disease can be evaluated.

Optical tomography for biomedical target is an evolving research area with emerging potential applications. In transillumination optical tomography, the filtered back projection (FBP) method is generally used for image reconstruction and the images represent a distribution of the optical attenuation coefficient. However, in practical optical imaging systems, refractive index mismatch at boundaries, such as the tissue surface, strongly affects optical attenuation. The surface effects are not constant even at the same part of the sample at different incident angles. Therefore, the surface effects introduce artifacts that obscure the internal structure and functional information in the laser CT images reconstructed by the FBP method. In this paper, we propose a simple correction method that could minimize the surface effects in laser CT images. The experiments were performed with the coherent detection imaging system based on the optical heterodyne detection technique. Experimentally determined attenuation coefficient corresponding to different incident angles was used to correct the surface effects. Improved target structures were demonstrated in the reconstructed laser CT images. Our correction method for laser CT image reconstruction is quite effective for visualizing internal structures with small variations in attenuation coefficients that would otherwise be masked by the dominant surface attenuation.

Polarization sensitive optical coherence tomography (PS-OCT) was used to determine the depth resolved Stokes parameters of light backscattered from highly scattering biological samples. Through simultaneous detection of the amplitude and relative phase of signal fringes in orthogonal polarization states formed by interference of light backscattered from turbid media and a mirror in the reference arm of a Michelson interferometer, changes in the Stokes parameters due to the optical phase delay between light propagating along the fast and slow axes of birefringent media were measured. Inasmuch as fibrous structures in many biological tissues influence the polarization state of light backscattered, PS-OCT is a potentially useful technique to image the structural properties of turbid biological materials. The method can also be applied to the investigation of birefringent properties in highly scattering materials such as ceramics and crystals.

In the past ten years, partial coherence interferometry has been developed and applied to high precision measurements of various biological and technical materials. This technique was extended to a high resolution, non contact imaging technique: optical coherence tomography (OCT). Recently, OCT was extended to perform polarization sensitive measurements and imaging. In this case, small phase variations caused by birefringence are measured and imaged. Small phase differences between adjacent beams can also be caused by other circumstances, e.g. by slight variations of geometric path length or refractive index. We present a method to measure these phase differences as a function of longitudinal and lateral position in the object. This method allows to determine the path length gradient with a resolution on the order of 10^-5. Furthermore, we report first results obtained in simple test objects and present first differential phase contrast OCT tomograms.

This work demonstrates the feasibility of OCT for identifying early osteoarthritic pathology. In addition to structural abnormalities, changes in collagen fiber organization, an indicator of very early osteoarthritis, were assessed with a polarization sensitive OCT system. A portable, real time, modular OCT system, suitable for both laboratory and clinical settings, has been developed. Preliminary in vivo imaging results obtained during partial knee replacement surgery are discussed.

Polarimetry, which is a comparison of the polarization state of light before and after it has interacted with a material, can be used to discriminate unscattered and weakly scattered photons from multiply scattered photons. Weakly scattered photons tend to retain their incident polarization state whereas highly scattered photons become depolarized; thus, polarization-based discrimination techniques can be used to image through tissue with decreased noise and increased contrast. Many previous studies investigating polarization- based discrimination have been conducted on tissue phantoms, with the ultimate goal being noninvasive imaging of breast tumors. We demonstrate here that linearly and circularly polarized light propagate differently in common tissue phantoms than in two independent techniques on tissue phantoms consisting of polystyrene and Intralipid microsphere suspensions, and on porcine adipose tissue and porcine myocardium. We show that contrary to expectations made from studies in the phantoms, linearly polarized light survives through more scattering events than circularly polarized light in both adipose tissue, which contains quasi-spherical scatterers, ad myocardium, which contains quasi-spherical and cylindrical scatterers. Differences between spherical and biological scatterers are discussed, along with the impact of tissue birefringence on degree of polarization measurements.

Color Doppler optical coherence tomography (CDOCT) is a functional extension of optical coherence tomography that can image flow in turbid media. We have developed a CDOCT system capable of imaging flow in real time. Doppler processing of the analog signal is accomplished in hardware in the time domain using a novel autocorrelation technique. This Doppler processing method was implemented arm of the interferometer. Image data was acquired, processed, and displayed in real time. We have demonstrated, for the first time, imaging of bi-directional flow with CDOCT in real time in a tissue-simulating phantom consisting of intralipid solution flowing in a glass capillaries submerged in intralipid solution. Issues of velocity resolution, imaging speed, and range of velocity measurement are discussed, as well as potential applications of real-time CDOCT.

Quantification of retinal blood flow may lead to a better understanding of the progression and treatment of several ocular disorders, including diabetic retinopathy, age- related macular degeneration, and glaucoma. Current techniques, such as fluorescein angiography and laser Doppler velocimetry are limited, failing to provide sufficient information to the clinician. Color Doppler optical coherence tomography (CDOCT) is a novel technique using coherent heterodyne detection for simultaneous cross- sectional imaging of tissue microstructure and blood flow. This technique is capable of high spatial and velocity resolution imaging in highly scattering media. We implemented CDOCT for retinal blood flow mapping in human subjects. No dilation of the pupil was necessary. CDOCT is demonstrated for determining bidirectional flow in sub- 100micrometers diameter vessels in the retina. Additionally, we calculated Doppler broadening using the variance of depth- resolved spectra to identify regions with large velocity gradients within the Xenopus heart. This technique may be useful in quantifying local tissue perfusion in highly vascular retinal tissue.

The effects of cooling, laser irradiation, and laser irradiation with cooling on blood vessels were investigated with Color Doppler Optical Coherence Tomography (CDOCT). CDOCT may contribute to an understanding of the dynamics of laser-blood vessel interactions and aid in better optimization of laser parameters to be used. In this study, hamster dorsal skin flap window vessels were irradiated with a KTP laser operating at 532 nm. Irradiation sites were imaged with CDOCT prior to, during, immediately after, and several days after irradiation. KTP laser parameters were: radiant exposures in the range of 7-14 J/cm², 3 mm spot size, and 10 ms pulse duration. Magnitude and color Doppler images provided information such as vessel size, depth, and changes in blood flow velocity. Vessel constriction, temporary occlusion, and changes in flow were frequent results of laser irradiation visualized with CDOCT. In addition, the effects of cooling alone were imaged with CDOCT and its effects on blood vessel flow and morphology were investigated before and after laser irradiation.

The arterial pulse profile registration method using an optical coherent photodetection in a diode laser is presented. An experimental device with pigtail laser diode has been developed. This device is able to detect pulsation profiles of major arteries with potentially useful information including pulse wave velocity and profile of pulse pressure. The basis of the registration is the self- mixing that occurs in the diode laser cavity when the radiation, scattered back by the skin into the laser, interferes with the field inside it and causes the changes of the laser pump current. These changes are being registered in two different ways simultaneously; with using a photodiode accommodated in the rear facet of the diode laser package and with a help of small resistance resistor from the chain of laser pump current. The delay of pulse wave in different regions of human body is measured relatively to ECG signal. Registered signals are sorted after digitalization and pre-processed using LabView for Windows environment.

We have developed a full field optical coherence microscopy (OCM) system operating at several frames per second. Depth ranging capability is compared between OCM and scanning confocal microscopy by imaging a test chart imbedded in 10 percent intralipid and imaging an onion. For sufficiently dense scattering, OCM was able to resolve test chart features and onion structures which were not detectable using confocal imaging alone.

Elastic light scattering is one of the most often used optical methods to analyze the cells agglutination reaction - the base of a great number of medical diagnostic test and biomedical investigations. The increase of the resolution of methods and apparatus towards the induced cells aggregation - the foundation of the reaction of agglutination, is quite an actual problem. The solution of this problem increases the reliability of the diagnostic test and gives an opportunity to achieve the diagnostic information in the cases when the traditional approaches do not lead to the diagnostic results. The attempt to increase the resolution of the immune reaction analyzer by means of ultrasonic waves action on the reagent mixture in vitro is taken in this paper. The RBC agglutination reaction which is usually used for the blood group type examination is chosen as an example of an object of the investigation. Different laser optical trains of the devices based on the turbidimetric and nephelometric methods and their combination are analyzed here. The influence of the ultrasonic wave time interval action and of the features of the sample preparation procedure on the resolution towards the agglutination process was investigated in this work. It is shown that the ultrasonic wave action on the reagent mixture leads to a large gain in the resolution of the device towards the RBC agglutination process. The experiments showed that the resolution of the device was enough to register the agglutination process even for the erythrocytes with weak agglutination ability when the reaction was invisible without ultrasonic action. It occurred that the diagnostic test time was more than by an order shortened due to the ultrasonic wave action. The optimal ultrasonic time interval action, the sample preparation technology and experimental technique were defined. The principle of the ultrasonic wave action on the cells agglutination process suggested here can be spread out on the immune molecular media. The results may be useful to develop new apparatus and methods for the aims of medical laboratory diagnostics.

In this research, we propose an algebraic reconstruction method suitable for the coherent detection imaging (CDI) based transillumination laser CT. When imaging highly scattering media such as tissues, the laser CT does not obey a simple absorption model, i.e., the Radon transform, because of the surface effects that arise due to refractive index mismatch at the object boundary. The surface effects degrade the reconstructed images quality. To compensate for the surface effects. However, a stable solution can not be obtained from the expression, since the equation system is always an underdetermined one. The constraint from the quantitative relationship between projections is considered to obtain the stable solution. The constraint ins based on the properties of CT and Gaussian beam. Accordingly, our reconstruction results in a least squares problem with a constraint. The problem is solved via the conjugate gradient method, whose convergence rate is relatively high. We demonstrate the effectiveness by applying the proposed method to experimental data acquired from a physical phantom.

The inclusion of radiation polarization considerably extends the sensitivity and the potentials of optical coherence tomography. The recorded signals are however skewed by using wide-band light sources and polarization sensitive elements, as well as by frequency dispersion of the objects under study. It is essential for such layered system with spatial anisotropy as eye cornea and sclera.

Technique of polarization imaging of multiple scattering tissues which contain the embedded large-scale inhomogeneous is discussed. This method is based on the measurements of the spatial distribution of the polarization degree of light scattered by tissue under study. Analysis of the influence of tissue scattering properties and geometry of experiment on the contrast and spatial resolution of reconstructed images by using the concept of optical paths distribution for partial components of scattered field is made. Interrelation between forms of spatial distributions of polarization degree and intensity distributions is discussed on the basis of theoretical analysis and experimental results obtained with model objects. Possibilities of the increase of contrast of reconstructed image as well as the restrictions of this technique are discussed.

Results of Monte-Carlo simulations Doppler shift are presented for the model of random medium that contain moving particles. The single-layered and two-layered configurations of the medium are considered. Doppler shift of the frequency of laser light is investigated as a function of such parameters as absorption coefficient, scattering coefficient, and thickness of the medium. Possibility of application of speckle interferometry for diagnostics in dentistry has been analyzed. Problem of standardization of the measuring procedure has been studied. Deviation of output characteristics of Doppler system for blood microcirculation measurements has been investigated. Dependence of form of Doppler spectrum on the number of speckles, integration by aperture, has been studied in experiments in vivo.

The present paper is concerned with the simulation, by random sampling, of the multiple scattering of photons for the purpose of solving near-IR radiation in complex multi- layer highly scattering media, which represent the structure of human skin in a simplistic manner. Direct weight Monte Carlo algorithm is imitating transport of photons between source detector areas by letting the photons carry out a random walk, each step of which is taken into account that provides information about time of photon presence in each layer of a medium. The last one makes it possible to estimate the depth sensitivity and the degree of spatial localization offered by fiber-optics probes of various geometries. Discussion of these limitations and potential possibilities of our simulation of skin model is given as well as a new suggestion for simulation of complex multi- layer tissues.

In the paper theoretical and experimental study of forming of interference pattern with a high contrast at the retina cataractous eye is presented. The high contrast of retinal fringes is reached by control of the parameters of incident beam with regular interference fringes. Experimental result have been done for the model objects that can be described in the framework of 'random phase screen' approximation. Some recommendations for clinical application are suggested.

Simple optical model of three-layer fluorescent phantom of biotissue with optically thick lowest layer was proposed. In the series of samples with varied 'epithelium' thickness and 'stromal' blood content the tendencies predicted by the model were observed.

A novel method of high speed grating-generated electronic coherence microscopy is applied to produce depth-lateral images of biological tissue without axial-lateral scanning. Axial-lateral scan is automatically performed by the stationary reflection diffraction grating installed in the Littrow configuration at the reference beam and a cylindrical lens installed in the sample beam. Using several 2D CCD array complex digital imags containing amplitude and phase values the depth-lateral reflections of biological tissue are reconstructed with a simple algorithm. The depth scan of 1.5 mm and the transversal coordinate image about 1.2 mm of the chicken tissue with a depth resolution of 17 micrometers , and a dynamic range about 70 dB are achieved. Final depth-lateral images are similar to OCT images and produced without any moving parts.

The longitudinal resolution of optical coherence tomography (OCT) is currently limited by the optical bandwidth of the light source, typically a superluminescent diodes, to approximately 10-15 micrometers . This resolution is insufficient to identify individual cells or to assess subcellular structures such as nuclei or mitotic figures. The ability to perform subcellular imaging with OCT could greatly enhance the detection of early neoplastic changes and improve early cancer diagnosis or the imaging of developing biological morphology. Higher resolution OCT would also improve specificity of diagnosis for several ocular diseases, such as glaucoma, which require precise, detailed imaging and measurement of retinal nerve fiber layer thickness. State of the art Kerr-lens mode-locked Ti:Al₂O₃ lasers using double chirped dispersion compensating mirrors can generate pulse durations of < 7 fs and bandwidths of 200 nm or more at 800 nm center wavelength. These pulse durations and bandwidths can be used for OCT, resulting in longitudinal resolutions of less than 2 micrometers . The use of such broad bandwidths also enables the extraction of localized, wavelength dependent absorption and scattering tissue characteristic by detecting the full interferometric fringe signa and using Fourier signal processing. In this paper we demonstrate an ultra-high-subcellular level resolution, spectroscopic OCT system based on a mode-locked Ti:Al₂O₃ laser. In vivo imaging of development biology specimens as well as preliminary in vivo spectroscopic OCT result are demonstrated.

We have developed a new technique to determine the optical properties of turbid media on a spatial scale of several 100 micrometers . This technique is based on transmission measurements into three different solid angles using a microspectrophotometer. An inverse Monte-Carlo simulation was employed to extract the optical properties from the sample under investigation. In this study, we investigated the optical properties of human brain tumor tissue. The transmission measurements were performed in the wavelength range from 400 nm to 800 nm for one spot on the sample. In addition, the histological inhomogeneity of the brain tumor was evaluated by probing the optical properties of different spots on the sample at a fixed wavelength. The resulting scattering coefficients varied between 6.0 and 7.9 mm^-1, the absorption coefficients between 0.50 and 0.92 mm^-1, and the anisotropy factors between 0.867 and 0.895. These result suggest that this microspectrophotometric technique is suitable to determine the optical properties of an inhomogeneous turbid media as for example a human brain tumor sample with a spatial resolution unattainable by conventional spectrophotometric techniques.