Ітеративний метод корекції артефактів при оптоакустичній реконструкції

Optoacoustic tomography is effective in applying to the visualization of objects that have a high coefficient of light absorption relative to the environment. Such tasks include, for example, defectoscopy, vascular imaging, detection and monitoring of tumors, diagnosis of porosity of composite materials, high-precision local measurement of the modulus of elasticity. However, the quality of optoacoustic images largely depends on factors such as noise (equipment or environmental noise) and distortion due to the characteristics of the model and the calculation algorithm. The article proposes an iterative algorithm for improving the quality of optoacoustic images, based on the observation that artifacts increase in magnitude with each iteration, while the nature and location of the distortions remain unchanged. Numerical simulations of the propagation of ultrasonic waves in environments close to soft biological tissues have been performed. In terms of eliminating distortion and artefacts inherent to the method of image reconstruction, an iterative filter was found to be highly effective The effectiveness of the approach is manifested in the use of a small number of iterations. Pages of the article in the issue: 98 - 107 Language of the article: UkrainianОптоакустична томографія ефективна при її застосуванні до задач візуалізації об’єктів, що мають підвищений коефіцієнт поглинання світла по відношенню до навколишнього середовища. До таких задач належить, наприклад, дефектоскопія, візуалізація кровоносних судин, виявлення і моніторинг пухлин, діагностика пористості композиційних матеріалів, високоточне локальне вимірювання модулів пружності. При цьому, якість оптоакустичних зображень в значній мірі пов’язана з такими факторами, як шум (шуми апаратури і навколишнього середовища) і спотворення, зумовлені особливостями самої моделі і розрахунковим алгоритмом. У роботі пропонується ітеративний алгоритм поліпшення якості оптоакустичних зображень, заснований на припущенні про постійність модельних і численних спотворень і наступному порівнянні (і коригуванні) відновлених зображень з оригінальними даними. Проведено чисельне моделювання поширення хвиль ультразвукового діапазону в середовищах, наближених до м’яких біологічних тканин. Показана ефективність підходу вже при використанні незначної кількості ітерацій

Поліпшення якості оптоакустичної візуалізації: співставлення фізичного та числового експерименту

Optoacoustic imaging is based on the generation of thermoelastic waves by heating an object in an optically inhomogeneous medium with a short laser pulse. The generated ultrasonic waves contain information about the distribution of structures with predominant optical absorption. Detection of acoustic perturbations on the surface of the object and the application of the backprojection algorithm are used to create a picture of the absorbed energy inside the environment. Conventional reconstruction methods lead to artifacts due to the peculiarities of the recovery algorithm. This study proposes an iterative procedure to reduce these artifacts. The algorithm minimizes the error between the measured signals and the signals calculated from the recovered image. The paper compares the results of processing optoacoustic signals implemented in numerical experiments with the results of physical experiments. It is shown that the quality of the recovered images improves even with a small number of iterations. Pages of the article in the issue: 46 - 56 Language of the article: UkrainianОптоакустична візуалізація заснована на генерації термопружних хвиль шляхом нагрівання об’єкта в оптично неоднорідному середовищі коротким лазерним імпульсом. Сгенеровані ультразвукові хвилі містять інформацію про розподіл структур з переважним оптичним поглинанням. Виявленні на поверхні об’єкта акустичні збурення та застосування алгоритмів реконструкції дозволяють відтворити картину поглиненої енергії всередині середовища. Звичайні методи реконструкції призводять до артефактів через особливості алгоритму відновлення. Це дослідження пропонує ітераційну процедуру для зменшення цих шкідливих спотворень. Алгоритм мінімізує похибку між виміряними сигналами та сигналами, розрахованими з відновленого зображення. У роботі порівнюються результати обробки оптоакустичних сигналів, реалізованих у чисельних експериментах, з результатами фізичних експериментів. Показано, що якість відновлених зображень покращується навіть при невеликій кількості ітерацій

VLBI observations of the G25.65+1.05 water maser superburst

This paper reports observations of a 22 GHz water maser 'superburst' in the G25.65+1.05 massive star-forming region, conducted in response to an alert from the Maser Monitoring Organisation (M2O). Very long baseline interferometry (VLBI) observations using the European VLBI Network (EVN) recorded a maser flux density of 1.2 × 104 Jy. The superburst was investipgated in the spectral, structural, and temporal domains and its cause was determined to be an increase in maser path length generated by the superposition of multiple maser emitting regions aligning in the line of sight to the observer. This conclusion was based on the location of the bursting maser in the context of the star-forming region, its complex structure, and its rapid onset and decay. © 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical SocietyRAB acknowledges support through the EACOA Fellowship from the East Asian Core Observatories Association. GO acknowledges support from the Australian Research Council Discovery project DP180101061 funded by the Australian Government, the CAS ‘Light of West China’ Program 2018-XBQNXZ-B-021, and the National Key R&D Program of China 2018YFA0404602. TH is financially supported by the MEXT/JSPS KAKENHI Grant Number 17K05398. BM acknowledges support from the Spanish Ministerio de Economía y Competitividad (MINECO) under grants AYA2016-76012-C3-1-P and MDM-2014-0369 of ICCUB (Unidad de Excelencia ‘María de Maeztu’). NS acknowledges support from Russian Science Foundation grant 18-12-00193. AMS is supported by the Ministry of Science and High Education (the basic part of the State assignment, RK No. AAAA-A17-117030310283-7) and by the Act 211 Government of the Russian Federation, contract No.02.A03.21.0006. JOC acknowledges support by the Italian Ministry of Foreign Affairs and International ..

Застосування нечіткої логіки при пошуку оптимального фільтру в задачах оптоакустики

Denoising is an important step in the early stage of signal preprocessing in optoacoustic applications. The efficiency of such modern noise removal methods as wavelet or curvlet filtering depends significantly on the numerical combinations and forms of wavelet transform parameters, and the multidimensional extension of such filters is rather non-trivial. These issues are serious obstacle for using of these highly effective filters in the tasks of optoacoustic reconstruction, especially in real laboratorial or medical practice. The objective of our study was to find the optimal filter, convenient for use in laboratorian and medical practice, when the types of noise are a priori unknown, and the filter settings should not take much time. In the offered work spatial filters which have only one parameter of adjustment - the size of a window are considered. Three-dimensional extensions of such well-established denoising techniques, as mean filter, median filter, their adaptive variants (Wiener spatial filter and modified median filter), as well as iterative truncated arithmetic mean filter were analyzed. The proposed filters were tested on a test set that contains versions of Shepp-Logan's three-dimensional phantom with mixtures of Gaussian and alpha-stable noise, as well as speckle noise. The identification of the best filter for simultaneous suppression of these types of interference was carried out using the theory of fuzzy sets. In our tests, a modified median filter and an iterative truncated arithmetic mean filter were rated as the best choice when the goal is to minimize aberrations when noise is not known a priory. Pages of the article in the issue: 43 - 54 Language of the article: UkrainianDenoising is an important step in the early stage of signal preprocessing in optoacoustic applications. The efficiency of such modern noise removal methods as wavelet or curvlet filtering depends significantly on the numerical combinations and forms of wavelet transform parameters, and the multidimensional extension of such filters is rather non-trivial. These issues are serious obstacle for using of these highly effective filters in the tasks of optoacoustic reconstruction, especially in real laboratorial or medical practice. The objective of our study was to find the optimal filter, convenient for use in laboratorian and medical practice, when the types of noise are a priori unknown, and the filter settings should not take much time. In the offered work spatial filters which have only one parameter of adjustment - the size of a window are considered. Three-dimensional extensions of such well-established denoising techniques, as mean filter, median filter, their adaptive variants (Wiener spatial filter and modified median filter), as well as iterative truncated arithmetic mean filter were analyzed. The proposed filters were tested on a test set that contains versions of Shepp-Logan's three-dimensional phantom with mixtures of Gaussian and alpha-stable noise, as well as speckle noise. The identification of the best filter for simultaneous suppression of these types of interference was carried out using the theory of fuzzy sets. In our tests, a modified median filter and an iterative truncated arithmetic mean filter were rated as the best choice when the goal is to minimize aberrations when noise is not known a priory. Pages of the article in the issue: 43 - 54 Language of the article: Ukrainia