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The design and principle of operation of the module for data acquisition and control of a broadband near-IR spectrometer are described. It was developed as the main interface device in the system for visualizing intraocular structures using optical coherence tomography. The achieved performance characteristics of this module make it possible to create a spectral diagnostic optical coherence tomography system with a high resolution value of a few micrometers. The USB 3.0 interface is used as the main computer communication channel, thus providing the compactness, portability, and versatility of the diagnostic system. The data-acquisition system is capable of operating against the background of computationally complex asynchronous procedures for synthesizing a continuous flow of tomographic images in real time, due to which the visualization system can operate in an interactive mode.

The paper describes the design of an optical coherence tomograph adapted for studying the state of the tympanic cavity of the human middle ear. We present the images obtained by the method of optical coherence tomography, which are characteristic of the norm and of the case of pathology – otitis media with effusion.

The application of computational methods to correct distortions in spectral-domain optical coherence tomography due to fast probe movements relative to a studied object is described. This technique is intended for use in endoscopy or in the study of external biological tissues using a handheld probe. The effectiveness of the method was confirmed experimentally.

A numerical method that compensates image distortions caused by random fluctuations of the distance to an object in spectral-domain optical coherence tomography (SD OCT) has been proposed and verified experimentally. The proposed method is based on the analysis of the phase shifts between adjacent scans that are caused by micrometer-scale displacements and the subsequent compensation for the displacements through phase-frequency correction in the spectral space. The efficiency of the method is demonstrated in model experiments with harmonic and random movements of a scattering object as well as during in vivo imaging of the retina of the human eye.

We study the causes of artifact appearance in the images obtained by the method of spectral domain optical coherence tomography with parallel reception of the optical-spectrum components, which are manifested in repetition and overlay of the structural elements of the images of the studied medium with a shift in depth. It is shown that nonidentity of the transfer characteristics of the channels of the multichannel photoreceiving elements is one of the sources of such artifacts. A numerical method for eliminating such artifacts is proposed and experimentally verified. This method is based on using the models whose parameters are estimated by the recorded signal and does not require a priori information on the transfer characteristics of the channels. The method efficiency is demonstrated during the experiments on the in vivo visualization of the human middle-ear elements.

The method for displacement correction along the slow axis of Optical Coherence Tomography (OCT) data volumes is presented. The method is based on the recursive replacement of the next displaced OCT measurements by the weighted summation of itself and the previous OCT measurement in the slow axis dimension already corrected for the displacement. The values of the appropriate weight multipliers were defined from the local correlation of the two measurements. The proposed method was used as a preprocessing step for Optical Coherence Angiography processing of the OCT data. Substantial reduction of the motion-induced stripe artifact was demonstrated.

We consider a cross-polarization optical coherence tomography system with a common path for the sounding and reference waves and active maintenance of the circular polarization of a sounding wave. The system is based on the formation of birefringent characteristics of the total optical path, which are equivalent to a quarter-wave plate with a 45° orientation of its optical axes with respect to the linearly polarized reference wave. Conditions under which any light-polarization state can be obtained using a two-element phase controller are obtained. The dependence of the local cross-scattering coefficient of light in a model medium and biological tissue on the sounding-wave polarization state is demonstrated. The necessity of active maintenance of the circular polarization of a sounding wave in this common path system (including a flexible probe) is shown to realize uniform optimal conditions for cross-polarization studies of biological tissue.

We develop an effective method for reducing nonequidistance when recording the spectral components of an interference signal in ultra-wideband spectral-domain optical coherence tomography. For this purpose, a corrector consisting of two identical prisms is used in a diffraction-grating spectrometer. The corrector rotation with respect to the diffraction-grating plane and a variation in the angle between the corrector elements allow one to adjust the equidistant spatial distribution of the spectral components in the photoreceiver array. It is shown experimentally that the developed method substitutes digital correction and leads to a significant reduction of the computational load in the optical coherence tomography device.

We present an improved analytical model of a spectrometer for optical coherence tomography (OCT), which more accurately describes the OCT in-depth sensitivity fall-off. The model considers the intrinsic spectral resolution of the dispersive element and the influence of additional components (inequidistance-correcting prism). The model is validated by experimental data obtained both from other studies and our own experiments. The influence of the frequency response of the CCD electrical circuit and the analog-to-digital converter to the OCT signal fall-off was also detected and was shown to be significant in some cases.

We describe a system of optical spectrum registration at the output of an interferometer with controlled phase shifts for an experimental device intended for visualizing the internal structure of an optically turbid specimen, using the method of spectral domain optical coherence tomography. A device for spectral domain optical coherence tomography based on a common-path optical scheme with a USB 3.0 interface for inputting data into a computer has been developed. An imaging speed of 91 912 A-scans/s has been attained. At the achieved speed, a series of live experiments were carried out to visualize the internal structure of skin tissues from a finger and front segments of an eye.

A method of numerical compensating of OCT image distortion provided by fluctuations of the distance to the object has been proposed and verified experimentally. The method is based on the analysis of inter A-scan phase shifts caused by micrometer-scale displacements, and the subsequent compensation of the displacements by phase-frequency correction in the spectral space. The efficiency of the method is demonstrated in model experiments with harmonic and random movements of a scattering object, as well as during in vivo imaging of the retina of the human eye.

An efficient technique for constructing the achromatic phase shift in the reference arm of spectral-domain OCT is presented. The technique is based on a wavelength-dependent optical delay line using a diffractive grating as a dispersive element. The high value of mirror artifact decreasing is demonstrated in common OCT setup.

We report realizations of OCT combining conventional structural imaging, polarization-sensitive one, as well as allowing for real-time angiographic, elastographic and lymphangiographic modalities with manual-operation capabilities. Among the main features of the developed device one can point out on-flight imaging of microvascular network with feedback for clinicians when performing angiography; in elastography - robust "vector" method of interframe phasevariation gradient estimation and stiffness quantification using reference silicone layers; lymphangiography utilizing pixel statistics beyond conventional amplitude thresholding, etc. These capabilities are ensured by the developed optical schemes of the probe, signal receiving parts, as well as computationally efficient signal processing methods. Examples of the developed device usage in preclinical and clinical applications are discussed (efficient criteria for PDT success; angiographic monitoring of complications during radiotherapy; elastographic classification of tumor and non-tumor regions; detailed imaging of fairly rapid transient and slowly varying deformations in laser-assisted reshaping of collagenous tissues; lymphangiography-based diagnostics in gynecology; otolaryngologic applications for diagnosing inner ear diseases, etc.)

The most valuable results for the use of OCT imaging in ENT diagnostics have been shown by Stephen Boppart and his group in Illinois Urbana-Champaign University. In 2016 this group demonstrated the possibility to reconstruct some viscosity properties of the effusion by the use of OCT providing some additional measurements. Our team have provided the pilot study on the possibility of detection of the effusion using the OCT device in 2014 13. The current work is devoted to improvement of Dr Boppart’s approach to examine the effusion viscosity. To provide the preliminary investigations we used the time-domain OCT device due to the reason of its clinical approval. This device provides about 200 A-scans per second, which is quite enough to register the Brownian movement of the scatterers in the middle ear effusion. All investigations were made by the use of thin (2.4 mm diameter) flexible forward-viewing probe 14 pushed through the standard ear mirror. The main disadvantage of the probe is the requirement of the contact between the tip and the tympanic membrane, which may cause some discomfort to the patient. In the order to enhance the image brightness behind the tympanic membrane the immersion was injected in the auditory meatus. The use of immersion also provides the reference level of scatterers mobility while the effusion viscosity was examined. The conventional OCT image of the eardrum demonstrates the high level of backscattering particles behind the membrane in the case of otitis media with effusion. Following 11, we switch scanning off and recorded images. The obtained image became time-resolved and moving scatterers are presented here as quite short horizontal lines on the image while the steady area is presented by long horizontal lines set. Dr Monroy used time-correlated analysis to estimate the mobility of particles suspended in the effusion. We propose to use the Fourier analysis of the image, which seems to be more informative. We implemented the 2D-Fourier transform to the OCT data recorded while the scanning was switched off. One can easily note the differences in the width of the spectrum between areas of eardrum, water immersion and effusion noting the effective spectral width. To numerically estimate the width of the Fourier image we fit every row data with the Gaussian shape. After that the FWHM parameters of the Gaussian shapes were used to obtain the in-depth profile of the particles “mobility. One can see that the obtained by proposed method particles “mobility” is quite different in cases of the water suspension and the effusion. We have proposed the method of estimation of the middle ear effusion viscosity using the Fourier analysis of the OCT data obtained by the fixed probe beam. The method provides the possibility to distinguish areas filled by water and effusion. We believe this approach to be useful in differentiation the grade of the otitis media with effusion in clinical conditions. This research was supported by Russian Science Foundation (project No 17-15-01507).

This work is dedicated to development of the OCT system capable to visualize blood vessel network for everyday clinical use. Following problems were solved during the development: compensation of specific natural tissue displacements, induced by contact scanning mode and physiological motion of patients (e.g. respiratory and cardiac motions) and on-line visualization of vessel net to provide the feedback for system operator.

An analogy between spectral-domain optical coherence tomography (SD OCT) data and broadband digital holography data is considered. Based on this analogy, a method for processing SD OCT data, which makes it possible to construct images with a lateral resolution in the whole investigated volume equal to the resolution in the in-focus region, is developed. Several issues concerning practical application of the proposed method are discussed. (laser biophotonics)

We have thoroughly investigated the method of simultaneous reception of spectral components with the achromatised quadrature phase shift between two portions of a reference wave, designed for the effective suppression of the 'mirror' artefact in the resulting image obtained by means of spectral domain optical coherence tomography (SD OCT). We have developed and experimentally tested a phase-shifting element consisting of a beam divider, which splits the reference optical beam into the two beams, and of delay lines being individual for each beam, which create a mutual phase difference of π/2 in the double pass of the reference beam. The phase shift achromatism over a wide spectral range is achieved by using in the delay lines the individual elements with different dispersion characteristics. The ranges of admissible adjustment parameters of the achromatised delay line are estimated for exact and inexact conformity of the geometric characteristics of its components to those calculated. A possibility of simultaneous recording of the close-to-quadrature spectral components with a single linear photodetector element is experimentally confirmed. The suppression of the artefact mirror peak in the OCT-signal by an additional 9 dB relative to the level of its suppression is experimentally achieved when the air delay line ismore » used. Two-dimensional images of the surface positioned at an angle to the axis of the probe beam are obtained with the correction of the 'mirror' artefact while maintaining the dynamic range of the image. (laser biophotonics)« less

Based on the fact that spectral domain (SD) optical coherence tomography (OCT) data can be treated as digital holography (DH) data acquired pointwise, we develop a spectral refocusing algorithm and show its ability to shift the focal region of OCT images obtained from SD OCT data acquired with a tightly focused scanning beam. Although refocusing itself depends on the refractive index of the studied media, we propose a procedure capable of restoring images with resolution equal to the resolution in the focal plane in the whole volume even in case of unknown refractive index of the media. As the proposed refocusing method operates with phases of the 3D Fourier spectrum of the SD OCT signal, it is very sensitive to the object motion during data acquisition. Thus, we also propose phase equalization preprocessing, which allows compensating the influence of such motions.

An improved method for suppressing image artefacts in spectral domain optical coherence tomography (SD OCT) and multiwave digital holography, caused by the influence of coherent noise in the course of successive registration of an autocorrelation component and informative signal is reported. The method allows complete suppression of all types of coherent noises, provided that the sample of values used to record the autocorrelation component satisfies the conditions of Kotelnikov's theorem: in SD OCT — for the transverse structure of the studied medium, in multiwave digital holography — for the envelop function of the radiation source frequency tuning spectrum.

A setup for visualizing the internal structure of media, which partially scatter radiation, using the spectral domain optical coherence tomography (OCT) method is described. The special complex of electron interface systems, ensuring the operating speed of the spectral domain OCT system at a level of 10000 A-scans (longitudinal scans along the depth) per second, high dynamic imaging range, and complete suppression of coherent noise peculiar to the spectral method has been designed to eliminate artifacts characteristic of this method.

The method for vessel visualization from optical coherence tomography (OCT) data is presented. The method is based on high-frequency filtration of the normalized absolute values of the scattered field measured with OCT. It is shown that in contrast with optical coherence angiography based on the processing of complex values of a scattered field, the proposed processing does not require motion correction preprocessing while providing resulting angiographic images of comparable quality.

The operating principle of an optical-fiber piezoe lectric modulator of the optical path in all-opti-cal-fiber interferometers is described. The control system of the optical-fiber piezoelectric modulator is composed of a controller based on a field programmable gate array, a digital-to-analog converter, an analog low-pass filter, and a power amplifier. A 4.4-m/s speed of chan ge in the optical length of the fiber has been attained with an error of 0.1% at a modulation length of the optical path of >1 mm.

An efficient technique for the separation of and compensation for coherent noise in spectral optical coherence tomography with parallel spectrum detection is proposed and validated. The coherent noise is separated during one exposure by modulating the mutual delay of the signal and reference waves by a certain law. It is shown that the influence of internal motions in an object on the quality of the coherent noise separation can be reduced by the modulation frequency increasing. The technique has been numerically and experimentally validated with the help of an optical coherence tomography (OCT) setup with a radiation source operating at a wavelength of 1277 nm and a width of the recorded spectrum of about 100 nm.

A method of OCT imaging with a resolution throughout the investigated volume equal to the resolution in the best-focused region is described. It is based on summation of three-dimensional scattered field distributions at the wavelengths determined by OCT source spectral decomposition. A method of finding parameters needed for algorithmic realization of the summation is also proposed. The proposed approaches are tested on several model media, including biological ones. As the proposed algorithm is phase sensitive, and phase stability is crucial, phase equalization preprocessing which allows compensating the phase error caused by object motion during scanning was proposed.

The problem of restoration Optical Coherence Tomography (OCT) images, acquired with tightly focused probing beam, in out-of-focus region for improving lateral resolution of the OCT has been considered. Phase stability issue has been discussed and phase equalization algorithm has been proposed. After phase equalization, the algorithm of digital refocusing, based on some methods from the DH, have been applied to the simulated as well as to experimental OCT data, acquired with tightly focused scanning beam to restore micrometer lateral resolution in the whole investigated volume.

An efficient technique of the coherent noise separation of and compensation for in spectral-domain optical coherence tomography (SD-OCT) is proposed and validated. The coherent noise is separated during one exposure by modulating the relative delay of the signal and reference waves by a certain waveform. It is shown that the influence of internal motions in an object on the coherent noise separation quality can be reduced by increasing of modulation frequency. The technique has been numerically and experimentally validated.

The work is devoted to improvement of spectral-domain OCT method to envelope real-time investigation of living biological tissue. Although spectral-domain OCT was positioned as a simple, high-speed and contrast OCT technique, researchers are faced with a family of difficulties during the development process. Problems of linear-in-wavenumber registration of spectral components and clearing of OCT-image of coherent noises are solved.

A method of OCT imaging with a resolution throughout the investigated volume equal to the resolution in the best-focused region is described. It is based on summation of three-dimensional scattered field distributions at the wavelengths determined by OCT source spectral decomposition. A method of finding parameters needed for algorithmic realization of the summation is also proposed. The proposed approaches are tested on several model media, including biological ones.