D. A. Terpelov

Coherent noise compensation in Spectral-Domain optical coherence tomography

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 control system for the optical-fiber piezoelectric modulator of the optical path

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.

Noniterative method of reconstruction optical coherence tomography images with improved lateral resolution in semitransparent media

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.

Digital refocusing in optical coherence tomography

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.

Electronic interface systems for goals of spectral domain optical coherence tomography

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.

Optical coherence tomography for noninvasive evaluation of the middle ear effusion (Conference Presentation)

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).

OCT-based angiography in real time with hand-held probe

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.

A data-acquisition and control system for spectral-domain optical coherence tomography with a speed of 91 912 A-scans/s based on a USB 3.0 interface

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.

Interferometric synthetic aperture microscopy with automated parameter evaluation and phase equalization preprocessing

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.

Coherent noise compensation improvement in spectral-domain optical coherence tomography

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.