Proceedings Volume 3251

Coherence Domain Optical Methods in Biomedical Science and Clinical Applications II

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Proceedings Volume 3251

Coherence Domain Optical Methods in Biomedical Science and Clinical Applications II

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Volume Details

Date Published: 24 April 1998
Contents: 7 Sessions, 33 Papers, 0 Presentations
Conference: BiOS '98 International Biomedical Optics Symposium 1998
Volume Number: 3251

Table of Contents

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Table of Contents

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  • Speckle and Fourier Technologies
  • Novel Coherence Domain Techniques and Instruments
  • In-Vivo Low-Coherence Interferometry and Tomography
  • Speckle and Fourier Technologies
  • Novel Coherence Domain Techniques and Instruments
  • Optical Doppler Tomography
  • Light Scattering and Fluorescence
  • Poster Session
  • Light Scattering and Fluorescence
  • Optical Polarization Technologies
  • Poster Session
  • In-Vivo Low-Coherence Interferometry and Tomography
Speckle and Fourier Technologies
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Coherent, low-coherent, and polarized light interaction with tissues undergoing refractive-index matching control
It is shown experimentally and theoretically that due to interaction of totally or partially coherent light beams with such tissues as the human eye sclera and skin which undergo the refractive indices matching the collimated and total transmission, diffuse reflection and speckle structure of transmitted beams are changing in accordance with transition from multiple to low-step scattering. The scleral samples in a final stage of tissue optical clearing have the same properties as an optical retarder.
Digital processing of noisy OCT signals in phase space
Kin Man Yung, Joseph M. Schmitt, Siu Lung Lee
OCT images, like those produced by ultrasound scanners, are contaminated with speckles. Speckle in OCT images occurs when light waves reflected by pairs of scatterers spaced by a distance of approximately (k + 1/2) (lambda) , for any integer k, add destructively to give a signal of very small amplitude. Rapid phase changes indicate the locations at which speckle occurs in OCT A-line signals. These changes can be detected by obtaining the unwrapped phase angle of quadrature- demodulated signals or zeros of z-transform of windowed A- lines. This paper discusses a zero-adjustment procedure (ZAP) that is capable of detecting and reducing speckle with the help of the signal phase. The method is evaluated on an analytical model and applied to OCT images of living skin.
Light beam shaping and homogenization (LSBH) by irregular microlens structure for medical applications
Vladimir A. Semchishen, Michael Mrochen, Vladimir N. Seminogov, et al.
Purpose: The increasing interest in a homogeneous Gaussian light beam profile for applications in ophthalmology e.g. photorefractive keratectomy (PRK) requests simple optical systems with low energy losses. Therefore, we developed the Light Shaping Beam Homogenizer (LSBH) working from UV up to mid-IR. Method: The irregular microlenses structure on a quartz surface was fabricated by using photolithography, chemical etching and chemical polishing processes. This created a three dimensional structure on the quartz substrate characterized in case of a Gaussian beam by random law distribution of individual irregularities tilts. The LSBH was realized for the 193 nm and the 2.94 micrometer wavelengths. Simulation results obtained by 3-D analysis for an arbitrary incident light beam were compared to experimental results. Results: The correlation to a numerical Gaussian fit is better than 94% with high uniformity for an incident beam with an intensity modulation of nearly 100%. In the far field the cross section of the beam shows always rotation symmetry. Transmittance and damage threshold of the LSBH are only dependent on the substrate characteristics. Conclusions: considering our experimental and simulation results it is possible to control the angular distribution of the beam intensity after LSBH with higher efficiency compared to diffraction or holographic optical elements.
Novel Coherence Domain Techniques and Instruments
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Automatized system of laser differential dermatoglyphic diagnostics
Irina A. Apollonova, Ilya V. Karasyov, Igor N. Spiridonov
The article introduces the results of the work on the development of methods and technical means for diagnostics of inborn diseases.
In-Vivo Low-Coherence Interferometry and Tomography
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In-vivo intraocular ranging by wavelength tuning interferometry
Christoph K. Hitzenberger, Manfred Kulhavy, Franz Lexer, et al.
Recently, wavelength tuning interferometry was suggested as an alternative technique for distance measurements. Compared to partial coherence interferometry, it has the advantages of needing no high precision mechanically moving components and the capability of measuring several distances simultaneously in very short time. We report on first measurements of intraocular distances in human eyes in vivo using a distributed Bragg reflector laser diode with a tuning range of 2 nm. We were able to measure the anterior chamber depth, the lens thickness, the vitreous depth, the axial eye length, and to estimate the thickness of the retina. The resolution is approximately 150 micrometer optical distance.
OCT for diagnosis of periodontal disease
Bill W. Colston Jr., Matthew J. Everett, Luiz Barroca Da Silva, et al.
We have developed a hand-held in vivo scanning device for use in the oral cavity. We produced, using this scanning device, in vivo OCT images of dental tissues in human volunteers. All the OCT images were analyzed for the presence of clinically relevant anatomical structures. The gingival margin, periodontal sulcus, and dento-enamel junction were visible in all the images. The cemento-enamel junction was discernible in 64% of the images and the alveolar bone presumptively identified for 71% of the images. These images represent, to our knowledge, the first in vivo OCT images of human dental tissue.
Endoscopic OCT for imaging of uterine body and cervix pathologies
Natalia M. Shakhova, Irina N. Kuznetzova, Natalia D. Gladkova, et al.
First results of endoscopic applications of optical coherence tomography (OCT) in gynecology are presented. We have studied mucosa of uterus, uterine cervix and vagina in vivo. Images of healthy endometrium in different stages of menstrual cycle have been recorded. For uterine cervix not only OCT data of normal state but some kids of pathology have been analyzed. Capability of OCT to identify alterations of mucosa makes this method promising for early diagnosis of tumors and precise guiding of excisional biopsy.
Speckle and Fourier Technologies
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Coherent signal analysis in color Doppler optical coherence tomography
Color Doppler optical coherence tomography (CDOCT) is a recent innovation which allows spatially localized flow velocity mapping simultaneous with micro-structural imaging. We present a theoretical model for velocity image formation in CDOCT. The equivalence between the heterodyne detector current power spectrum in CDOCT and the optical source power spectrum is established. We show that stochastic modifications of the detected electronic spectrum by fluctuating scatterer distributions in the flow field give rise to unavoidable velocity estimation inaccuracies, as well as to the fundamental trade-off between the maximum velocity image acquisition rate and the estimated velocity precision. Novel algorithms which permit high fidelity depth-resolved measurements of velocities in turbid media with optimal frame rate are also reported.
Novel Coherence Domain Techniques and Instruments
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Chirp optical coherence tomography with high resolution and artifact reduction using tunable near-infrared laser
Dominik Hoelscher, Udo Haberland, Daniel Pieknick, et al.
Chirp optical coherence tomography (C-OCT) has become an alternative solution for imaging scattering media. This technique uses frequency modulated laser sources without a mechanical moving reference mirror as it is necessary in conventional coherence tomography. Images of scattering phantoms using an electrically tunable laser diode with a spatial resolution of about 400 micrometer in air had shown the capability of this tomographic principle. The new setup contains an External Cavity Laser (ECL) with a center wavelength of 780 nm. Due to the wide usable tuning range of the ECL an improved spatial resolution could be obtained compared with the electrically tunable laser diode. Having only one reflection in the object the wide bandwidth of the ECL yields a peak with the full width at half maximum less than 20 micrometers. Images of phantoms with known dimensions and scattering properties made with this arrangement are presented. Measurement of movement and motion artifacts demands special frequency modulation of the light source. Suitable methods to obtain useful information like location and velocity of moving objects as well as reducing artifacts are proposed. Combining C-OCT with Laser Doppler Perfusion Imaging (LDPI) requires conveniently prepared sweep functions.
High-resolution real-time 3D imaging using time-gated photorefractive holography
Mary Tziraki, Richard Jones, Duncan Parsons-Karavassilis, et al.
A real time, high-resolution coherence gating system to image through turbid media has been demonstrated. Using the technique of photorefractive holography with Multiple Quantum Well (MQW) devices, high-resolution depth resolved images through 13 MFP have been recorded. The fast response time (less than 0.4 ms) and the high optical quality of the MQW devices allowed images to be acquired, in real-time, direct to a video cassette recorder. The spectral versatility of this system has been demonstrated by recording images at wavelengths from 800 - 850 nm.
Dynamic coherent focus for transversal resolution enhancement of OCT
Franz Lexer, Adolf Friedrich Fercher, Harald Sattmann, et al.
One of the major problems of optical coherence tomography (OCT) is limited transversal resolution. A small focus can certainly be generated using a small confocal beam parameter. But then transversal resolution becomes severely dependent on the position of the beam focus within the object. Hence to achieve optimal transversal resolution within the whole object, the focus of the illuminating beam has to be shifted during the coherence scan throughout the object depth. To maintain coherence the optical path length of the reference beam has to be shifted by the same amount. In our experimental setup we use an optical design which makes it possible to shift the focus of the measurement beam without changing the optical path length of the reference beam. We call this technique dynamic coherent focus because a focus is created that remains coherent to the reference beam during the whole coherence scan. Using a Ronchi ruling resolution target with 200 line pairs/mm we demonstrate that the transversal resolution is better than 5 micrometer. In the cross sectional image of a human cornea in vitro epithelium and the endothelium layers are visible with a longitudinal resolution of approximately 14 micrometer and transversal resolution of better than 5 micrometers. The cellular structure of the endothelium is resolved.
Optical Doppler Tomography
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Investigating laser/blood-vessel interaction with color Doppler optical coherence tomography
A non-invasive method of imaging laser irradiated blood vessels, and of tracking the healing response, has been achieved using Color Doppler Optical Coherence Tomography (CDOCT). This method may increase understanding of the mechanisms behind treatment of vascular disorders such as port wine stains. The CDOCT system uses a superluminescent diode with a center wavelength of 1280 nm. Pulsed dye and KTP lasers operating at 585 and 532 nm, respectively, were used to irradiate rat and hamster dorsal skin flap window models. The window model is a chronic preparation which exposes subdermal blood vessels while maintaining a thickness of normal skin. Irradiation sites were imaged with CDOCT prior to and immediately after laser irradiation, and at intervals up to several days following irradiation. The CDOCT signal was processed to provide both magnitude and color Doppler images. The Doppler signal provides an estimate of the blood flow velocity. The response of blood vessels to radiant exposures above and below the threshold for vessel coagulation was measured. An increase in the blood vessel backscattered signal was observed as blood and vessel walls were coagulated. Changes in blood flow velocity were noted in cases where vessels constricted or flow became occluded.
Monte Carlo simulation studies of optical coherence tomography (OCT) and optical Doppler tomography (ODT)
Tore Lindmo, Derek J. Smithies, Zhongping Chen, et al.
A Monte Carlo simulation model has been developed to study how OCT and ODT imaging results are influenced by multiple scattering effects. For shallow optical depths [less than 3 mean free path (mfp) units] in intralipid (g equals 0.7), the number of detected backscattered photons was found to follow the extinction-single-backscatter model, and accurate mean values and small standard deviations for axial and lateral point spread functions were observed. For deeper depths, the positional accuracy and precision of backscatter was rapidly lost, and the number of detected photons no longer decreased with increasing focus depth in the nonabsorbing medium. For strongly forward-directed scattering in blood (g equals 0.99), depth profiles of the number of detected backscattered photons only approached the extinction-single- backscatter model for very shallow depths (optical depth less than 2 mfp units, metric depth less than 13 micrometers). However, quite accurate and precise point spread functions were observed even for large optical depths (40 mfp units). Doppler detection of blood flow was studied by simulating a 100 micrometer diameter horizontal blood vessel placed 200 micrometers below the surface in 2% intralipid. Simulated depth profiles of average Doppler frequency demonstrated good accuracy in absolute velocity values and localization of flow boundaries (3 - 4% deviation). Doppler frequency noise was observed in backscattering from regions underneath the vessel.
Diagnostic blood-flow monitoring during therapeutic interventions using color Doppler optical coherence tomography
Siavash Yazdanfar, Manish D. Kulkarni, Richard C. K. Wong, et al.
A recently developed modality for blood flow measurement holds high promise in the management of bleeding ulcers. Color Doppler optical coherence tomography (CDOCT) uses low- coherence interferometry and digital signal processing to obtain precise localization of tissue microstructure simultaneous with bi-directional quantitation of blood flow. We discuss CDOCT as a diagnostic tool in the management of bleeding gastrointestinal lesions. Common treatments for bleeding ulcers include local injection of a vasoconstrictor, coagulation of blood via thermal contact or laser treatment, and necrosis of surrounding tissue with a sclerosant. We implemented these procedures in a rat dorsal skin flap model, and acquired CDOCT images before and after treatment. In these studies, CDOCT succeeded in identifying cessation of flow before it could be determined visually. Hence, we demonstrate the diagnostic capabilities of CDOCT in the regulation of bleeding in micron-scale vessels.
New concept for laser Doppler vibrometry of the human ear
Hans-Jochen Foth, Ralf Kretner
While several technical problems could be solved and the reproducibility of the technique appeared to be high enough, the individual variations between different persons seems to limit the importance of using laser Doppler vibrometry for clinical diagnosis. The complexity of the motions of the middle ear bones with frequency dependent superpositions of translational and rotational modes is seen as chance for a yield of information about middle ear diseases. A new concept is presented which relays on two laser beams guided under different angle onto the same spot to determine between the different kinds of motions. The theoretical and basis and first experimental tests are described to evaluate the reliability of this concept.
Light Scattering and Fluorescence
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Dynamic light scattering particle-size measurements in turbid media
Dynamic light scattering (DLS) particle size measurments are reported for turbid systems. These include particulate dispersions and suspensions of macromolecules in a wide (7 nm - 800 nm) particle size (diameter) range which look as transparent as water and as turbid as milk (turbidity approximately 6 - 7 orders of magnitude higher than water) and samples of lenticular and skin tissues. Our results indicate a significant improvement in achieving non-invasive, compact, robust, and remotely operated DLS probes which are able to push the envelope of DLS utilization to extremely turbid samples of a variety of particle type and size of macromolecules which were hitherto not possible.
Autofluorescence of tissue surrounding malignant tumors
Wolfgang Lohmann, Rainer M. Bohle, Wolf-Bernhard Schill, et al.
In vitro fluorescence measurements on pap smears of ascites, pleura, or Douglas confirmed results obtained previously with different types of tissue: Cancer tissue fluoresces hardly and is surrounded by a 'fluorescence belt.' Investigations of cytological smears (e.g. Pap smears) have revealed the possible participation of granulocytes in this 'immune' reaction. Furthermore, there seems to be obvious differences in the fluorescence response of pap smears between ovarial- carcinomas and peritoneal carcinomas based on ovarial carcinoma. This observation cannot be explained yet. Because of its sensitivity and specificity the fluorescence method can be used as an additional tool for the evaluation of the tumor invasion front. Preferably it might be used for frozen sections of biopsies and surgical excisions.
Bioelectric response of plants to local low-intensity irradiation in the spectral range of 330 to 1300 nm
Yury H. Shogenov, Elena A. Mironova, Vera Yu. Moiseenkova, et al.
The choice of the qualitative method of estimation of the reaction of a living system to the light irradiation is the main problem in the measurements of spectra of action. It was demonstrated earlier that the bioelectric reaction (BER) on a low-level local laser irradiation can be used for these measurements. We determined the dependence of the BER of a plant on the wavelength (lambda) of the coherent and incoherent irradiation. In the visible spectral range the dependence of BER on (lambda) coincides with chlorophyll absorption spectrum and the peak at 1015 - 1300 nm is related probably with water absorption. The dependence of BER on I is of the threshold type. The wavelength dependence of the transmittance of an intact green leaf nearly coincides with its photoacoustic spectrum. Thus, the proposed nondisturbing methods make it possible to determine the optical parameters of a living plant.
Poster Session
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Elastic light scattering on reagent mixture in the immune reaction process in vitro
Valeri A. Doubrovski, K. N. Dvoretski, Vyacheslav F. Kirichuk, et al.
The paper is devoted to computer simulation of elastic light scattering on reagent mixture during the immune reaction process in vitro. The immune reaction was analyzed in the limits of the 3-stages process of antigen-antibody complexes aggregation. Antibodies were treated as bivalent biomolecules, antigens were performed by 2, 3-valent biomolecule or polyvalent cells. Two variants of the problem solution of light scattering on the biological objects chosen were analyzed-Rayleigh-Gans-theory, the approach, and Mie theory, the preference was given to the first one. The optimum of the immune reaction output was revealed at quite a definite ratio of initial reagents concentrations. This optimum is analog of experimentally a well known phenomenon -- the 'zone of equivalence.' It's shown that the form of the 'zone of equivalence' both depends upon the kind of experimental procedure and the ratio of the antigen, antibody sizes. This result is preferably to take into consideration while one tries to optimize the medical diagnostic procedure based on the immune approach. It was revealed that the scattered light power correlates with the immunochemical kinetics not adequately sometimes. That fact may be useful to interpret the experimental investigations and at the same time it may give a principal possibility to use nephelometry for the aims of immune metrology.
Light Scattering and Fluorescence
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Does turbid-media time- and space-resolved reflectance depend on the different moments of the scattering phase function?
Sigrid Avrillier, Bernard Gelebart, Eric Tinet, et al.
We have already demonstrated that some optical coefficients of turbid media ((mu) a, (mu) s') can be derived from time and space resolved backscattered light measurements in the case of semi-infinite geometry, or multi-layered media, using the experimental results obtained far enough from the illumination area, that is where and when the diffusion approximation is valid. Our purpose is now to determine if this type of measurements can be used to explore the different moments of the scattering phase function. The same experimental set-up consisting of a titanium-sapphire pulsed laser and a streak camera was therefore used to measure the reflectance at earlier times and closer to the light source. Experiments were performed with aqueous solutions of calibrated latex microspheres. Various values of the spheres diameter were alternately used in order to vary the anisotropy factor g. Comparison with Monte-Carlo simulations were achieved for the resolution of the inverse problem. The influence of the shape of the phase function was also investigated.
Optical Polarization Technologies
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Birefringence characterization of biological tissue using optical coherence tomography
Matthew J. Everett, Klaus Schoenenberger, Bill W. Colston Jr., et al.
A polarization sensitive optical coherence tomography (OCT) system is developed and used to measure birefringence in porcine myocardium tissue, producing 2-D cross-sectional images of the tissue birefringence. These birefringence images are then used to quantify thermal damage in the tissue. Signal to noise issues which cause systematic measurement errors are analyzed to determine the regime in which such measurements are accurate. The advantage of polarization sensitive OCT systems over standard OCT systems in avoiding image artifacts caused by birefringence is also demonstrated.
Coherent light depolarization by multiple scattering media and tissues: some fundamentals and applications
Dmitry A. Zimnyakov, Valery V. Tuchin, Arjun G. Yodh, et al.
Relationships between decorrelation and depolarization of coherent light scattered by disordered media are examined by using the conception of the photon paths distribution functions. Analysis of behavior of the autocorrelation functions of the scattered field fluctuations and their polarization properties allows us to introduce generalized parameter of scattering media such as specific correlation time. Determination of specific correlation time has been carried out for phantom scattering media (water suspensions of polystyrene spheres). Results of statistical, correlation and polarization analysis of static and dynamic speckle patterns carried out in the experiments with human sclera with artificially controlled optical transmittance are presented. Some possibilities of applications of such polarization- correlation technique for monitoring and visualization of non- single scattering tissue structures are discussed.
Poster Session
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Laser visualization system for intermediate product material heterogeneity
Igor N. Spiridonov, Nina M. Verenikina, Georgiy Y. Petlyakov
The possibility of visualization of anomal crystallization zones in polymeric material intermediate products by using an optical-electronic model of a test bench has been shown. The visualization is necessary during following production stages: the periodical technical process control, the sample control and the waste rejection. An original scheme of the model construction providing a solution of the raised problem by means of a minimal device composition has been suggested. The model experimental researches for different light sources of the visual and infra-red spectral ranges and different illuminators have been carried out in order to determine an influence of the lighting conditions and light spectral composition on the heterogeneity image quality. The results have permitted to formulate demands to the light source and forming illumination system of the test bench reasonably. The main attention has been given to the diagnostics of the heterogeneity near the top of the intermediate product that is the most typical, difficulty measured, and that exerts essential influence on the product quality. The investigation results for two intermediate product groups of different firms are given. A comparison method of the crystallization zone sizes with the technological norm has been suggested.
Ultrasound Dopplerography of abdomen pathology using statistical computer programs
Irina V. Dmitrieva, Sergei M. Arakelian, Alberto Raimundo W. Wapota
The modern ultrasound dopplerography give us the big possibilities in investigation of gemodynamical changes in all stages of abdomen pathology. Many of researches devoted to using of noninvasive methods in practical medicine. Now ultrasound Dopplerography is one of the basic one. We investigated 250 patients from 30 to 77 ages, including 149 men and 101 women. The basic diagnosis of all patients was the Ischaemic Pancreatitis. The Second diagnoses of pathology were the Ischaemic Disease of Heart, Gypertension, Atherosclerosis, Diabet, Vascular Disease of Extremities. We researched the abdominal aorta and her branches: Arteria Mesenterica Superior (AMS), truncus coeliacus (TC), arteria hepatica communis (AHC), arteria lienalis (AL). For investigation we use the following equipment: ACUSON 128 XP/10c, BIOMEDIC, GENERAL ELECTRIC (USA, Japan). We analyzed the following componetns of gemodynamical changes of abdominal vessels: index of pulsation, index of resistance, ratio of systol-dystol, speed of blood circulation. Statistical program included the following one: 'basic statistic's,' 'analytic program.' In conclusion we determined that the all gemodynamical components of abdominal vessels had considerable changes in abdominal ischaemia than in normal situation. Using the computer's program for definition degree of gemodynamical changes, we can recommend the individual plan of diagnostical and treatment program.
Statistical characteristics of scattered light for determining biochemical parameters of whole blood
Alexander N. Korolevich, Natalya P. Prygun
Correlation spectroscopy methods are widely used to study dynamical, morphological and optical parameters of particles. This work makes an attempt to explore these methods (in particular, due to their expressively) for diagnosing whole blood under normal and pathological states (cardiovascular diseases). Not only morphological characteristics of blood elements are known to change under diseases, but also its biochemical compositions does. The paper is directed to investigating the correlation between optical characteristics of light scattered by blood and its biochemical parameters.
Monte Carlo simulation of polarized backscattering in spatially limited random media
Irina L. Maksimova, Vera F. Izotova, Sergey V. Romanov
Investigation of the polarization characteristics of scattered light can be effectively used for diagnosis of biotissues and bio-objects. Usually the whole indicatrices of scattered light can not be measured in vivo. So the investigation of polarized backscattered light is of great interest. The high concentration of scatterers in such objects requires the multiple scattering effects to be accounted for. In this work the Monte-Carlo method was used to describe the multiple scattering of polarized light. Trajectories of each migrating photon were traced by this method. Probability density of scattering directions are determined according to the Mie formulas with accounting for the polarization of each photon. As a result, the Stokes vectors of scattered light were calculated. So, we have determined the changes of polarization characteristics caused by the variations of the dimensions and concentrations of scatterers and by the geometry of medium. The influence of the order of scattering on the depolarization of scattered light also have been investigated. We present the patterns of spatial distribution of intensities backscattered polarized light. Calculations were performed for the systems of isotrope spherical scatterers and the obtained results were compared with the experimental data of measurement in the cross-polarized channel described in.
Multiple scattering effects under conditions of coherent-laser-radiation light scattering in the eye lens
Irina L. Maksimova, Nadezhda L. Larionova
This paper deals with the problem of calculating the polarization and spatial characteristics of laser radiation scattered by the eye lens. The light scattering matrix (LSM) and angular dependencies of the LSM elements were obtained. Multiple scattering effects simultaneously with the degree of near order for scattering particles were taken into account.
Optical and morphological investigation of hair of patients with Chediak Higashi syndrome
Narahari V. Joshi, Jose Goyo-Rivas
The Chediak-Higashi syndrome (CHS) is a rare disease and is very often observed in a single family. In Venezuelan Los Andes area, its appearance is not uncommon. One of the peculiar aspects of CHS patients is the color, texture and structure of the hairs. We have, therefore, investigated structure, morphology and composition of hairs and compared those properties with that of normal human subject grown in the same geographical region. A few hairs were cut along its length and their fluorescence was investigated. For CHS patients, dark patches were observed. Investigations of chemical compositions of these regions were carried out of using Energy Dispersive Analysis and it was found the presence of Na, K and Ca ions. Fluorescence spectral studies were carried out at room temperature. Observed spectra reveal two peaks, however, those were not useful for positive identification of CHS.
Dynamic peculiarities of motility of some species of micro-organisms by quasi-elastic light scattering
Sergei N. Bagayev, Victor Aleksandrovich Gusev, Valery A. Orlov, et al.
The results of the study of the laser radiation scattered on living micro-organisms in water suspension in time and spectral domain are presented. The comparison of the dynamic characteristics of the motility of bacteria Escherichia and Pseudomonas is made.
Use of speckled speckles and low-coherent speckles in the imaging of biofluid flow velocity
Formulas relating to diffraction of focused Gaussian beam from narrow blood microvessel have been derived. Vessel has been considered as a set of moving random screens. The correlation function of intensity fluctuations of statistically inhomogeneous speckled speckles has been studied with regard to flow measurement. Dependencies of statistical characteristics of biospeckles with a small number of scatterers on the number of scattering screens and on the length of coherence of incident light have been analyzed. It has been shown that the value of Doppler bandwidth in the scattered light essentially depends on the spatial velocity distribution in the blood flow.
Laser interferometer with a sharply focused beam as a tool for optical tomography
Vladimir P. Ryabukho, Vladimir L. Khomutov, Valery V. Tuchin, et al.
On the base of spatial-temporal analogy in properties of the optical fields the equivalence of temporal and spatial photodetector averaging of light interference field is shown. In the low-coherence interferometry the interferential signal is vanished when optical path difference becomes more than light coherence length lc approximately equals (lambda) 2/(Delta) (lambda) . This value determines the accuracy of the testing of the reflecting layer location. The analogous vanishing of the interferential signal can be realized by a spatial averaging of the interference field in the case of the sufficiently wide receiving photodetector aperture. For such averaging Michelson interferometer with a laser beam focussed on the object surface can be used. In this case interferential signal is vanished when the surface displacement is more than a focussed beam parameter (delta) ((Delta) z) equals (lambda) /(NA)2, where NA is a numerical aperture of the objective. With NA approximately equals 1 only a few oscillations of interferential signal is observed. It is corresponding to advanced achievements of the low-coherence interferometry. The experimental results show a high testing accuracy of the position of smooth and rough surfaces, the thickness of transparent coating attached to the rough surface and multilayered scattering objects. Thus, interferometers with a sharply focussed probing beam can be consider as a good alternative for the low-coherence interferometry and can be used in coherent optical tomography.
Light source for low-coherence interferometry and imaging
Mikhail I. Sverdlov, Garif G. Akchurin, S. A. Alaverdyan, et al.
Light emitting module, which consist of superluminescent diodes (SLD) with spectral width approximately 20 nm full width of half maximum (FWHM), simple optical objective and driver for constant output power has been designed. An influence of the length of coherence of the illumination source used on the correlation characteristics of spatial distributions of speckle intensity is investigated.
In-Vivo Low-Coherence Interferometry and Tomography
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Integrated endoscopic OCT system and in-vivo images of human internal organs
Alexander M. Sergeev, Valentin M. Gelikonov, Grigory V. Gelikonov, et al.
First results of endoscopic applications of optical coherence tomography (OCT) for in vivo studies of human mucosa in respiratory, gastrointestinal, urinary and genital tracts are presented. A novel endoscopic OCT (EOCT) system has been created that is based on the integration of a sampling arm of an all-optical-fiber interferometer into standard endoscopic devices using their biopsy channel to transmit low-coherence radiation to investigated tissue. We have studied mucous membranes of esophagus, larynx, stomach, urinary bladder, uterine cervix and endometrium as typical localization for carcinomatous processes. Images of tumor tissues versus healthy tissues have been recorded and analyzed. Violations of well-defined stratified healthy mucosa structure in cancered tissue is distinctly seen by EOCT, thus making this technique promising for early diagnosis of tumors and precise guiding of excisional biopsy.