Patent RU-2767875-C1 (RU)
Title: Method for assessing the stability of an atherosclerotic plaque by intravascular optical coherence tomography
Inventor: Frolov Sergei Vladimirovich
IPC: A61B6/03
Filed: 2020-12-14
Granted: 2022-03-22
Abstract: FIELD: medicine. 
     SUBSTANCE: invention relates to medicine, namely to diagnostics. A threshold limiter is applied to the processed three-dimensional source data in order to determine voxels with a signal level above or below the threshold, determine the signal from the blood vessel, calculate the distance from the extreme voxel of the atherosclerotic plaque to the centre of the blood vessel, identify calcium deposits, identify the crescent-shaped structure, calculate the areas of all structures included in the atherosclerotic plaque, including at least calcium deposits and a crescent-shaped structure, calculate the total area of the atherosclerotic plaque as the sum of the structures contained therein, calculate the percentage of each of the structures in the total area of the atherosclerotic plaque. The processed data therein are time-synchronised interference signals of intravascular optical coherence tomography from the wall of the examined section of the blood vessel with an atherosclerotic plaque, as well as information on the current blood pressure and blood flow velocity in the vicinity of the intravascular sensor. The layers of the wall of the blood vessel, fibrous cap, lipid core, and the area of calcium deposition are identified. The crescent-shaped structure is therein considered to be a combination of the lipid core and the fibrous cap. Interference signals are pre-processed by combining the functions of threshold filtering, morphological erosion, and morphological dilation. Preliminary identification of the structures of the wall of the examined blood vessel with an atherosclerotic plaque is conducted by signal intensity, using tabular information about the optical properties of structures contained in the atherosclerotic plaque. The geometry of the boundaries of the identified structures is adjusted by comparing information about the value of Young modulus for each of the identified structures with the tabular information about the biomechanical properties of all structures contained in the atherosclerotic plaque. The value of Young modulus is calculated as a quotient of dividing the product of the longitudinal dimensions of the deformable area, the normal component of the flow velocity vector, and the difference between the systolic and diastolic pressure in the examined area of the blood vessel by the modulus of absolute displacement of structures in the same area. A pulse wave, absolute displacements of structures are therein accounted for as a deforming influence. The size of the deformable area is calculated by comparing the structural images of intravascular optical coherence tomography for systole and diastole times by reference points. The normal component of the velocity vector is calculated by decomposing said vector along the coordinate axes, followed by rotation. The thickness of the fibrous cap, after specifying the boundaries thereof accounting for the value of Young modulus, is calculated within separate sections along lines with a step equal to the spatial resolution of the intravascular optical coherence tomograph, in a direction parallel to the straight line connecting the extreme voxel of the atherosclerotic plaque and the centre of the blood vessel in the given section. The arrays of thicknesses of the lipid core and calcium deposits are determined similarly. The difference between the sum of the thicknesses of the fibrous cap and calcium deposits on one side and the thickness of the lipid core on the other side is calculated. The atherosclerotic plaque is therein considered stable if the total thickness of the fibrous cap and areas of calcium deposition for all analysed lines exceeds the thickness of the lipid core, otherwise the examined atherosclerotic plaque is considered unstable. 
     EFFECT: method allows for an increase in the accuracy of assessment of the stability of atherosclerotic deposits provided by accounting not only for the percentage of calcium deposition, but also for the minimum thickness of the fibrous cap, wherein the above structures are identified by collecting and analysing information on the optical and biomechanical properties of the examined atherosclerotic plaque. 
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