A method for studying atherosclerotic plaques on the walls of large blood vessels is described. The method is based on a study of raw data of intravascular optical coherence tomography (IOCT). Identification of fat constituents, calcium, cholesterol crystals, macrophage clusters, blood clots, etc. within the areas of atherosclerotic lesions of blood vessels is based on the study of two parameters only. The intensity of the A-scan interference signal is the first parameter, and the biomechanical properties (primarily Young's modulus) are the second analyzed parameter. The pulse wave is used as the least traumatic deforming effect. The magnitude of the deforming effect in blood vessels is calculated using averaging of the blood pressure differences. This data is acquired using an invasive pressure probe. Structural IOCT-images corresponding to the moments of systole and diastole are selected from the sequence of raw data. Both IOCT-images are segmented and classified by signal intensity. Primarily, identification of segments is based on reference data of the optical properties of the atherosclerotic plaques’ components. The segments with similar geometrical locations and signal intensity are grouped into pairs. The centroids are calculated for all segments. The absolute displacements of the segments are estimated by the displacements of the centroids. The area of deformation is considered to be equal to the scanning area of the applied intravascular probe. The dimensions of the deformable area for the set of segments of two analyzed images are calculated with respect to the coordinate axes and then averaged. The biomechanical properties of the segments are calculated according to classical formulas and are used to update values of the primary identification of the structural components of atherosclerotic plaques. Information about the geometric characteristics and internal structure of atherosclerotic plaques are used to identify their properties and current stability.
A color coded flow mapping method for ophthalmic applications of optical coherence tomography (OCT) is presented. The described algorithm was developed taking into account the specific changes in the interference signal caused by the characteristics of the biological fluid flow through the scanning plane. A key feature of the algorithm is the multistage analysis of fluctuations in the speckle pattern of OCT-images. Speckle pattern is identified by using the color reverse function, convolution, threshold limitation, morphological digital processing, convex hull generation, gradient based processing and image recoding. The interference signal intensity peaks caused by sharp changes of the optical properties at the boundaries of highly scattering layers (the retina has a multilayered structure) are smoothed out for the specklestructures mapping. The correlation coefficients of the same parts of the sequence of structural OCT-images are calculated not for pixel intensities, but for previously identified speckle pattern. The variance values between nonoverlapping parts of the same structural image are calculated also not for pixel intensities, but for previously identified speckle pattern. Absolute flow velocity quantitative evaluation is made by a standard way, i.e. taking into account the time intervals between acquisition moments of the corresponding parts of the interference signal.
A method for cerebral vessel tissue-like phantom making and a device for the realizing pulsating flows in them are described. The blood vessels are molded together with models of the organs carrying them. A blood vessel phantom is a hollow structure with three-layered walls mimicking its geometry, structure, inhomogeneity of optical and mechanical properties. The model of an organ serves only for fixing the hollow structure of it in anatomically correct position and therefore is homogeneous in texture and properties. The source of information about the geometry of the imitated blood vessel is the results of angiography of a real clinical case. The three-layered structure of phantoms is justified by the anatomical features of real blood vessels (outer layer - adventitia, middle layer - media, inner layer - intima). The three-layered structure is made by layer-by-layer application of a transparent two-component liquid silicone on a wax base. Each layer is distinguished by its thickness and unique concentration of special admixtures (titanium dioxide nanoparticles and absorbing colorant). Mechanical properties of the layers are changed by varying the concentration of the components of the transparent liquid silicone. The phantom is solidified and then heated to remove the wax. Then the phantom of a blood vessel is placed in a mold of a corresponding organ. The mimicking organ is also made from a two-component transparent liquid silicone with special admixtures. Both proximal and distal ends of the hollow structure are connected with fork catheters. A 1% of intralipid solution in water is used to simulate blood flow in the phantom. Streaming velocity control of a blood-mimicking liquid is provided by a syringe pump. Pulsating flow is generated by the controlled twisting of the tube between the pump and the phantom of a blood vessel. A vibration motor is used to change the velocity profile. The described experimental model of a hydrodynamic phantom of a blood vessel is used in combination with intravascular optical coherence tomography for checking compression elastography properties.
A method for evaluating the viscosity of turbid biological fluids and pharmaceuticals is described. The proposed method is based on digital analysis of optical coherence tomography (OCT) raw data. The scanning probe of the OCT-system is positioned perpendicular, a drop of a tested liquid is applied to a scanning probe of the system, so that it hangs freely from its surface under the action of surface tension and gravity. Then, a movable glass slide touches the lower part of the drop ensuring minimal contact. In a correct experiment, the contact area of the upper side (base) of the drop with the solid surface of the scanning probe should be many times larger than the contact area of the lower side of the drop with the movable glass slide. The first three-dimensional structural OCT-image (C-scan) is obtained in the above-described position. The movable slide is driven in perpendicular direction to the scanning probe. A series of three-dimensional structural OCT-images of a deformed drop is acquired during the slide displacement. The deforming surface area is calculated as the area of the corresponding segment of the first C-scan. The magnitude of the deforming force for different moments is calculated based on the characteristics of the controlled motion of the movable plate. The ratio of the deforming force to the area of the deforming surface allows estimating the shear stress at the corresponding moments of time. The shear rate is estimated from the displacement C-scan control points of the drop surface for the known time periods of each deforming step. The dynamic viscosity is estimated by the classical formula, as the ratio of shear stress to shear rate. The results are digitally processed, averaged, are to be used in dynamic viscosity determination and presented to the end user.
A method for tissue-like phantoms preparation for cerebral arteries with aneurysms is presented. Magnetic resonance angiography (MRA) images are used as a source of structural information about the geometry of the simulated cerebral arteries and surrounding brain tissue. Blood vessels were reconstructed as hollow structures with three-layer walls. The inner layer corresponds to the intima of the real vessel, its middle layer - media, and the outer layer - adventitia. The basis for the reconstruction of the first layer of hollow structures and mold for casting surrounding brain tissue were 3D printed. Hollow structures were reconstructed applying layer-by-layer method with use of two-component transparent silicone gel with a variable mass fraction of two components, A and B. Variation the mass fraction of the components and thickness for each layer allows achieving the necessary stress-related properties. Equivalence to the real structure of the cerebral arteries and optical properties were achieved by variation of mass fraction of the additives for each layer matrix. A powder of titanium dioxide was used as scattering particles and a special gel colourant for silicone was applied as an absorbing agent. Hollow structures were added in the mold for casting surrounding brain tissue simulator, so that their geometrical arrangement corresponds to associated blood vessels. The proximal and distal ends of hollow structures are equipped with forked catheters.
A method for evaluation of the shear modulus for the large blood vessel walls is described. Structural images of the investigated part of the blood vessel wall with aneurysm are sequentially obtained using intravascular optical coherence tomography (IOCT) system for at least several cardiocycles. B-scans correspondent to diastole and shear deformation stages between systole and diastole are taken for the evaluation from a sequence of structural images. The pulse wave is considered to be the only deforming stimulus. The surface area of the deforming force is considered to be equal to the scanning area of the IOCT system. B-scans’ profiles are processed and plotted according to the average truncated level of the interference signal intensity. These profiles are divided into overlapping blocks. Shear deformation is estimated for overlapping blocks by the abscissa projection of the average displacement vector. The dimensions of the deformed region are to be equal to corresponding coherence probing depth. Shear modulus in the point of interest of the blood vessel wall is calculated using the classical formula and verified using known values of the Young's modulus and Poisson's ratio.
The retina phantom and a method for making pulsating flows of a fluid in human eye retina vessels are described. The retina phantom was made from two-component transparent silicone. A special gel colourant for silicone was used as an absorbing agent and TiO2 (titanium dioxide) nanoparticles were used as scatterers. The central retinal artery and vein were constructed as a set of related extended cavities in the phantom. The proximal and distal ends of the cavities were connected to standard catheters. First catheter was connected to the fluid supply tank using a flexible transparent tube. The second catheter was connected to a container for the out coming fluid using another tube. Hemodynamic setup for fluid supply contains: i) a tank with sufficient quantity of the fluid; ii) a pump for making a laminar fluid flow; iii) a unit to make laminar to turbulent flow transformation regime; iv) flow meter and control unit. Periodically repeated controlled twisting of a flexible tube with a laminar flow was used to make pulsations. Vibrations were used to simulate flow changes associated with patient movements and tremor. The described system can be used for developing quantification algorithms to study relative changes and absolute values of blood flow velocity using ophthalmic Doppler optical coherence tomography systems.
А numerical simulation algorithm of the interference signal acquired from biological fluids’ flow in Doppler optical coherence tomography (OCT) system is described. The suggested numerical approach has four key features: i) hydrodynamic characteristics of the part of the geometric layout in the intravascular space are not static, but dynamically change in numerical simulation of the photon transport; ii) dynamic changes include fluctuations of the optical characteristics and geometry of the parts of the intravascular space and were made for all pixels (B-scan) or voxels (Cscan) of the acquired data; iii) pixels and voxels of the intravascular space are considered to have the optical properties either of blood plasma or of the red blood cells; iv) the flow velocity is different for different types of pixels (voxels) which replace each other in the intravascular space: v) velocity value is chosen to obtain the desired shape of the flow velocity profile. The numerical model of the flow with a complex structure in soft biological tissues was implemented as the dedicated software using the LabVIEW package. The interference signal (A-scan) simulating software was successfully tested using hydrodynamic phantoms and can be used to study flow characteristics and their dynamic changes.
The method for obtaining functional images of human brain or another soft biological tissue and its phantoms based on the time-resolved diffuse optical tomography is described. The developed method is based on the principles of near infrared spectroscopy, in particular on the increased probing depth in optical transparency window and the differences in the absorption spectra of oxygenated and deoxygenated blood. The key feature of the approach is fast search and dynamical visualization of the most oxygenated sections of an investigated object using improved mapping algorithm for localization of absorbing inhomogeneities. Hydrodynamic phantoms with pulsatile blood flow in the thickness of biological tissues were used for validation of the described method.
A borderline reconstruction algorithm of optical structure disturbances of biomedical objects is described. The key features of it: (I) determination of the coordinates of the centers and effective size of each absorbing and scattering inhomogeneity in an investigated biological tissue, (II) refinement of the convex and concave parts of the boundary of each spherical inhomogeneity which is followed by smoothing the resulting structural image. The refinement of the parts of the boundary of a spherical inhomogeneity was made by adding or subtracting additional spheres. Centers of additional spheres were determined stochastically in the neighborhood of the boundary of the spherical inhomogeneity. Radii of additional spheres were calculated as one quarter of the length of the distance from the center of the additional sphere to the center of the spherical inhomogeneity.
The method of longitudinal elasticity modulus evaluation for the large blood vessel wall is presented. It is based on obtaining and computer analyzing structural images of the same section of the investigated blood vessel wall at the moments correspondent to systole and diastole. Endoscopic optical coherence tomography system with a forward-side probe was used by the structural images raw data acquisition. Digital analysis of structural images includes noise reduction, detection of control points, combination them together and calculation of relative displacements. The Young's modulus was calculated taking into account the surface area of the scanning region, the coherence probing depth and the magnitude of the deformation impact of the pulse wave.
The algorithm for obtaining high-quality structural images in endoscopic optical coherence tomography with a reduced level of speckle noise is described. The key features of the developed algorithm are the multilevel filtering and morphological digital processing of structural images. Structural images of soft biological tissues in vivo and tissue-like phantoms are shown. The suggested algorithm can be used to improve quality of structural images not only in optical methods of visualization and non-destructive testing, but also in ultrasonic ones.
The method of Doppler color mapping of one specific (previously chosen) velocity in a turbulent flow inside biological tissues using optical coherence tomography is described. The key features of the presented method are: the raw data are separated into three parts, corresponding to the unmoving biological tissue, the positively and negatively directed biological fluid flows; the further independent signal processing procedure yields the structure image and two images of the chosen velocity, which are then normalised, encoded and joined. The described method can be used to obtain in real time the anatomical maps of the chosen velocities in normal and pathological states. The described method can be applied not only in optical coherence tomography, but also in endoscopic and Doppler ultrasonic medical imaging systems.
High-quality OCT structural images reconstruction algorithm for endoscopic optical coherence tomography of biological tissue is described. The key features of the presented algorithm are: (1) raster scanning and averaging of adjacent Ascans and pixels; (2) speckle level minimization. The described algorithm can be used in the gastroenterology, urology, gynecology, otorhinolaryngology for mucous membranes and skin diagnostics in vivo and in situ.
Optical structure disturbances localization algorithm for time-resolved diffuse optical tomography of biological objects is described. The key features of the presented algorithm are: the initial approximation for the spatial distribution of the optical characteristics based on the Homogeneity Index and the assumption that all the absorbing and scattering inhomogeneities in an investigated object are spherical and have the same absorption and scattering coefficients. The described algorithm can be used in the brain structures diagnosis, in traumatology and optical mammography.
A method of optical coherence tomography (OCT) structural images reconstruction using Monte Carlo simulations is described. Biological object is considered as a set of 3D elements that allow simulation of media, structure of which cannot be described analytically. Each voxel is characterized by its refractive index and anisotropy parameter, scattering and absorption coefficients. B-scans of the inner structure are used to reconstruct a simulated image instead of analytical representation of the boundary geometry. Henye-Greenstein scattering function, Beer-Lambert-Bouguer law and Fresnel equations are used for photon transport description. Efficiency of the described technique is checked by the comparison of the simulated and experimentally acquired A-scans.
The regularities of movement of the Photon Density Normalized Maximum (PDNM) in highly scattering media such as biological tissues are described. An improved model of the optical properties of turbid media based on the diffusion approximation to the Radiative Transfer Equation (RTE) is used for identifying regularities of PDNM movement. Numerical simulations confirmed that in homogeneous cylindrical objects PDNM always moves to the geometric centre of the object. In the case of single absorbing inhomogeneities PDNM moves towards the point which is symmetrical to the geometric centre of it with respect to the center of the object. In the presence of a single scattering inhomogeneity PDNM moves towards its geometric centre.
A new method of an optical inhomogeneity detection in strongly scattering media having optical properties of biological tissue Time-Resolved Diffuse Optical Tomography (TR-DOT) is described. The method is based on preliminary processing of a three-dimensional surfaces obtained from the set of time-resolved data in the Cartesian coordinate system, followed by their conformal transform into surfaces in the cylindrical coordinate system. The key feature of the method is application of Late-Arriving Photons (LAP) diffusely transmitted through turbid objects. (i) LAP of each TPSF (Time Point Spread Function) standardized for a minimum angle; (ii) the resulting normalized function approximated by straight lines; (iii) normalized function is modified with the additional factor, K; (iv) final transform to the cylindrical coordinates.
Depth resolved coherence gating along with Doppler shift detection of the carrier frequency is used for one predetermined velocity mapping in different flows. Bidirectional rapid scanning optical delay of optical coherence tomography system is applied in the reference arm. Tilted capillary entry is used as a hydrodynamic phantom to model a sign-variable flow with complex geometry. Structural and one specific velocity images are obtained from the scanning interferometer signal processing in the frequency domain using analog and digital filtering. A standard structural image is decomposed into three parts: stationary object, and positive and negative velocity distributions. The latter two show equivelocity maps of the flow. The final image is represented as the complexation of the three.
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