Alexander B Konovalov | Russian Federal Nuclear Center - Zababakhin Institute of Applied Physics (RFNC-VNIITF), Snezhinsk, Russia (original) (raw)

Papers by Alexander B Konovalov

Вестник Южно Уральского Государственного Университета Серия Образование Здравоохранение Физическая Культура, 2006

Computer Optics, Sep 30, 2023

The paper presents an original approach to time-domain reflectance fluorescence molecular tomogra... more The paper presents an original approach to time-domain reflectance fluorescence molecular tomography (FMT) of small animals. It is based on the use of early arriving photons and state-of-the-art compressed-sensing-like reconstruction algorithms and aims to improve the spatial resolution of fluorescent images. We deduce the fundamental equation that models the imaging operator and derive analytical representations for the sensitivity functions which are responsible for the reconstruction of the fluorophore absorption coefficient. The idea of fluorescence lifetime tomography with our approach is also discussed. We conduct a numerical experiment on 3D reconstruction of box phantoms with spherical fluorescent inclusions of small diameters. For modeling measurement data and constructing the sensitivity matrix we assume a virtual fluorescence tomograph with a scanning fiber probe that illuminates and collects light in reflectance geometry. It provides for large source-receiver separations which correspond to the macroscopic regime. Two compressed-sensing-like reconstruction algorithms are used to solve the inverse problem. These are the algebraic reconstruction technique with total variation regularization and our modification of the fast iterative shrinkage-thresholding algorithm. Results of our numerical experiment show that our approach is capable of achieving as good spatial resolution as 0.2 mm and even better at depths to 9 mm inclusive.

Journal of Electronic Imaging, 2018

Abstract. The paper presents an original hybrid image reconstruction algorithm ART-TVS for few-vi... more Abstract. The paper presents an original hybrid image reconstruction algorithm ART-TVS for few-views computed tomography of strongly absorbing media. It is based on the well-known algebraic reconstruction technique (ART), regularization of interim results through minimization of the total variation norm (TV-regularization), and a method of adaptive segmentation, which is a modernization of the known region growing algorithm. It is shown that the ART-TVS algorithm does not give stripe artifacts even if the number of views is very small (eight or less). ART-TVS reconstruction results for two numerical models of metal shells are compared with those obtained with the ART-TV algorithm (ART with TV-regularization and without adaptive segmentation), the iterative Potts minimization algorithm (IPMA), and our MART-AP algorithm (multiplicative ART with a priori information) we developed earlier for few-views discrete tomography. It is shown that ART-TVS outperforms ART-TV and IPMA and is comparable with MART-AP in reconstruction accuracy. Also, ART-TVS converges markedly faster than IRMA in cases where strongly underdetermined systems are treated. The algorithm we propose also demonstrates quite satisfactory resistance to projection data noise that is inherent in tomography of strongly absorbing media.

Journal of Biomedical Optics

Significance: Fluorescence molecular lifetime tomography (FMLT) plays an increasingly important r... more Significance: Fluorescence molecular lifetime tomography (FMLT) plays an increasingly important role in experimental oncology. The article presents and experimentally verifies an original method of mesoscopic time domain FMLT, based on an asymptotic approximation to the fluorescence source function, which is valid for early arriving photons. Aim: The aim was to justify the efficiency of the method by experimental scanning and reconstruction of a phantom with a fluorophore. The experimental facility included the TCSPC system, the pulsed supercontinuum Fianium laser, and a three-channel fiber probe. Phantom scanning was done in mesoscopic regime for three-dimensional (3D) reflectance geometry. Approach: The sensitivity functions were simulated with a Monte Carlo method. A compressed-sensing-like reconstruction algorithm was used to solve the inverse problem for the fluorescence parameter distribution function, which included the fluorophore absorption coefficient and fluorescence lifetime distributions. The distributions were separated directly in the time domain with the QR-factorization least square method. Results: 3D tomograms of fluorescence parameters were obtained and analyzed using two strategies for the formation of measurement data arrays and sensitivity matrices. An algorithm is developed for the flexible choice of optimal strategy in view of attaining better reconstruction quality. Variants on how to improve the method are proposed, specifically, through stepped extraction and further use of a posteriori information about the object. Conclusions: Even if measurement data are limited, the proposed method is capable of giving adequate reconstructions but their quality depends on available a priori (or a posteriori) information. Further research aims to improve the method by implementing the variants proposed.

Journal of Biomedical Optics, 2022

Significance: Fluorescence molecular lifetime tomography (FMLT) plays an increasingly important r... more Significance: Fluorescence molecular lifetime tomography (FMLT) plays an increasingly important role in experimental oncology. The article presents and experimentally verifies an original method of mesoscopic time domain FMLT, based on an asymptotic approximation to the fluorescence source function, which is valid for early arriving photons. Aim: The aim was to justify the efficiency of the method by experimental scanning and reconstruction of a phantom with a fluorophore. The experimental facility included the TCSPC system, the pulsed supercontinuum Fianium laser, and a three-channel fiber probe. Phantom scanning was done in mesoscopic regime for three-dimensional (3D) reflectance geometry. Approach: The sensitivity functions were simulated with a Monte Carlo method. A compressed-sensing-like reconstruction algorithm was used to solve the inverse problem for the fluorescence parameter distribution function, which included the fluorophore absorption coefficient and fluorescence lifetime distributions. The distributions were separated directly in the time domain with the QR-factorization least square method. Results: 3D tomograms of fluorescence parameters were obtained and analyzed using two strategies for the formation of measurement data arrays and sensitivity matrices. An algorithm is developed for the flexible choice of optimal strategy in view of attaining better reconstruction quality. Variants on how to improve the method are proposed, specifically, through stepped extraction and further use of a posteriori information about the object. Conclusions: Even if measurement data are limited, the proposed method is capable of giving adequate reconstructions but their quality depends on available a priori (or a posteriori) information. Further research aims to improve the method by implementing the variants proposed.

Monte Carlo Methods and Applications, 2022

The paper describes a sensitivity function calculation method for few-view X-ray computed tomogra... more The paper describes a sensitivity function calculation method for few-view X-ray computed tomography of strongly absorbing objects. It is based on a probabilistic interpretation of energy transport through the object from a source to a detector. A PRIZMA code package is used to track photons. The code is developed at FSUE “RFNC–VNIITF named after Academ. E. I. Zababakhin” and implements a stochastic Monte Carlo method. The value of the sensitivity function in a discrete cell of the reconstruction region is assumed to be directly proportional to the fraction of photon trajectories which cross the cell from all those recorded by the detector. The method’s efficiency is validated through a numerical experiment on the reconstruction of a section of a spherical heavy-metal phantom with an air cavity and a density difference of 25 Ṫhe proposed method is shown to outperform the method based on projection approximation in case of reconstruction from 9 views.

Presentation at the 8th International Symposium on Optics and Biophotonics (Saratov, Russia, September 2020), 2020

One of the most effective approaches for improving the spatial resolution of fluorescent tomogram... more One of the most effective approaches for improving the spatial resolution of fluorescent tomograms is to apply the state-of-the-art reconstruction algorithms based on compressed sensing (CS) theory. The paper presents a numerical experiment on fluorescent image reconstruction where we compare two CS algorithms: the algebraic reconstruction technique (ART) with total variation regularization, ART-TV, and the ART with fast iterative shrinkage-thresholding, ART-FIST. For modeling measurement data and constructing the sensitivity matrix we assume a virtual fluorescence tomograph with a scanning fiber probe that illuminates and collects light in reflectance geometry with source-receiver separations corresponding to the macroscopic regime. We show that ART-FIST outperforms ART-TV in reproduction accuracy and is capable of achieving as good spatial resolution as 0.2 mm at depths to 9 mm inclusive, and is quite competitive in this sense with mesoscopic fluorescence tomography.

Presentation at the 4th International Symposium on Optics and Biophotonics, (Saratov, Russia, September 2016), 2016

The paper develops an original method of evaluating the weight functions for time-domain diffuse ... more The paper develops an original method of evaluating the weight functions for time-domain diffuse optical tomography in parallel-plate transmission geometry. We first derive analytical expressions for the case of a semi-infinite scattering medium by using Green’s function of the nonstationary diffusion equation. Then we assume that photon migration near the receiver on the opposite boundary can be similar in the cases of a semi-infinite space and a thick flat layer, find the positions of the equivalent and equivalent inverse sources inside the flat, and apply the formulas obtained to evaluate the weight functions for parallel-plate transmission geometry. The efficiency of our approach is demonstrated through a numerical experiment wherein the rectangular scattering phantoms with absorbing and scattering inhomogeneities are recovered using the hybrid method that combines algebraic reconstruction technique and total variation regularization.

Russian Journal of Nondestructive Testing

Digital tomosynthesis system (DTS) has been increasingly used in chest X-ray imaging with a limit... more Digital tomosynthesis system (DTS) has been increasingly used in chest X-ray imaging with a limited-projection angle image reconstruction method. Image reconstruction methods in chest digital tomosynthesis (CDT) have fundamental impacts on image characteristics. Among these methods, iterative algorithm provides the additional benefits of chest X-ray imaging. However, there is almost no research that maximum-likelihood expectationmaximization (MLEM) method in CDT system. Thus, the purpose of this study was (1) to develop MLEM reconstruction algorithm based on CDT system and (2) to quantitatively compare the image characteristics with respect to the total angular range and iteration number as applied this system. For that purpose, we performed both simulation using MATLAB program and experimental studies. Tomography was performed linearly with a maximum ±30 • total angular range and then we acquired Shepp-Logan and PMMA-Aluminum (Al) phantom images using 120 kVp X-ray source for simulation and experiment, respectively. We evaluated and compared the MLEM reconstructed image characteristics using root-mean-square error (RMSE) and signal difference-to-noise ratio (SDNR) with various total angular ranges and iteration numbers. According to the results, we can acquire improved image characteristics as the number of iterations and the number of projections increased. Also, we found optimized iteration number for 20 iteration numbers in our CDT system geometry because there were few changes of image characteristics over 20 iteration numbers. In conclusion, we have presented usefulness and effectiveness of developed CDT image reconstruction algorithm.

2012 5th International Symposium on Communications, Control and Signal Processing, 2012

The paper considers a new iterative algorithm for tomographic image reconstruction when a very li... more The paper considers a new iterative algorithm for tomographic image reconstruction when a very limited number of projections are registered. The algorithm uses a priori information on the discrete values of the object function to be reconstructed and is based on the known multiplicative algebraic reconstruction technique (MART). The new algorithm we called MART-AP organizes a cycle of “external” iterations where the image is corrected at each iteration, using the MART and an image mask synthesized with the help of a priori information. It has been shown in numerical experiment that the algorithm proposed helps completely remove streaklike artifacts usually present on the tomograms which were reconstructed in conditions of strongly incomplete data.

Computer Optics

Two algorithms of few-view tomography are compared, specifically, the iterative Potts minimizatio... more Two algorithms of few-view tomography are compared, specifically, the iterative Potts minimization algorithm (IPMA) and the algebraic reconstruction technique with TV-regularization and adaptive segmentation (ART-TVS). Both aim to reconstruct piecewise-constant structures, use the compressed sensing theory, and combine image reconstruction and segmentation procedures. Using a numerical experiment, it is shown that either algorithm can exactly reconstruct the Shepp-Logan phantom from as small as 7 views with noise characteristic of the medical applications of X-ray tomography. However, if an object has a complicated high-frequency structure (QR-code), the minimal number of views required for its exact reconstruction increases to 17–21 for ART-TVS and to 32–34 for IPMA. The ART-TVS algorithm developed by the authors is shown to outperform IPMA in reconstruction accuracy and speed and in resistance to abnormally high noise as well. ART-TVS holds good potential for further improvement.

International Journal for Numerical Methods in Biomedical Engineering, 2020

The paper presents an original approach to time-domain reflectance fluores-cence molecular tomogr... more The paper presents an original approach to time-domain reflectance fluores-cence molecular tomography (FMT) of small animals. It is based on the use of early arriving photons and state-of-the-art compressed-sensing-like reconstruction algorithms and aims to improve the spatial resolution of fluorescent images. We deduce the fundamental equation that models the imaging operator and derive analytical representations for the sensitivity functions which are responsible for the reconstruction of the fluorophore absorption coefficient. The idea of fluorescence lifetime tomography with our approach is also discussed. We conduct a numerical experiment on 3D reconstruction of box phantoms with spherical fluorescent inclusions of small diameters. For model-ing measurement data and constructing the sensitivity matrix we assume a virtual fluorescence tomograph with a scanning fiber probe that illuminates and collects light in reflectance geometry. It provides for large source-receiver separations which correspond to the macroscopic regime. Two compressed-sensing like reconstruction algorithms are used to solve the inverse problem. These are the algebraic reconstruction technique with total variation regularization and our modification of the fast iterative shrinkage-thresholding algorithm. Results of our numerical experiment show that our approach is capable of achieving as good spatial resolution as 0.2 mm and even better at depths to 9 mm inclusive.
K E Y W O R D S: early arriving photons, fluorescence molecular tomography, fluorescent inclusions, reconstruction algorithms, sensitivity functions, spatial resolution

Proceedings of SPIE, 2020

The paper is devoted to a new method of time-domain lifetime fluorescence molecular tomography. I... more The paper is devoted to a new method of time-domain lifetime fluorescence molecular tomography. It is based on the use of early arriving diffuse photons and original measurement data, which are determined for the individual time gates of the diffuse temporal responses for fluorescence and exiting radiation. The paper presents in short the theoretical foundation of the method and describes a numerical experiment on the separate reconstruction of fluorophore absorption coefficient and fluorescence lifetime for 3D reflectance geometry that is suitable for small animal imaging. We show our first reconstruction results for the 3D scattering object region 11x11x8 mm 3 in size with two spherical fluorescent inclusions 1 mm in diameter. The ways how to improve these results in the future are discussed.

Computer Optics, 2019

В статье сравниваются два алгоритма малоракурсной томографии: итерационный алго-ритм минимизации ... more В статье сравниваются два алгоритма малоракурсной томографии: итерационный алго-ритм минимизации функционала Поттса и алгебраический алгоритм реконструкции с TV-регуляризацией и адаптивной сегментацией. Оба алгоритма ориентированы на восстанов-ление кусочно-постоянных структур, используют теорию опознавания со сжатием и совме-щают процедуры реконструкции и сегментации изображений. На уровне численного экспе-римента показано, что каждый из алгоритмов способен точно восстанавливать фантом Шеппа-Логана всего по 7 ракурсам. Когда же речь идет о восстановлении объекта, имею-щего сложную высокочастотную структуру (QR-кода), минимальное число ракурсов, необ-ходимое для точной реконструкции, возрастает до 17-21 в случае алгоритма реконструкции с TV-регуляризацией и адаптивной сегментацией и до 32-34 в случае итерационного алго-ритма минимизации функционала Поттса. Показано, что разработанный авторами статьи алгоритм реконструкции с TV-регуляризацией и адаптивной сегментацией имеет некоторое преимущество над итерационным алгоритмом минимизации функционала Поттса по таким критериям, как точность и скорость реконструкции, а также устойчивость к шуму проекци-онных данных. Отмечено, что алгоритм реконструкции с TV-регуляризацией и адаптивной сегментацией имеет хороший потенциал для дальнейшего совершенствования.

Journal of Electronic Imaging, 2018

The paper presents an original hybrid image reconstruction algorithm ART-TVS for few-views comput... more The paper presents an original hybrid image reconstruction algorithm ART-TVS for few-views computed tomography of strongly absorbing media. It is based on the well-known algebraic reconstruction technique (ART), regularization of interim results through minimization of the total variation norm (TV-regularization), and a method of adaptive segmentation, which is a modernization of the known region growing algorithm. It is shown that the ART-TVS algorithm does not give stripe artifacts even if the number of views is very small (eight or less). ART-TVS reconstruction results for two numerical models of metal shells are compared with those obtained with the ART-TV algorithm (ART with TV-regularization and without adaptive segmentation), the iterative Potts minimization algorithm (IPMA), and our MART-AP algorithm (multiplicative ART with a priori information) we developed earlier for few-views discrete tomography. It is shown that ART-TVS outperforms ART-TV and IPMA and is
comparable with MART-AP in reconstruction accuracy. Also, ART-TVS converges markedly faster than IRMA in cases where strongly underdetermined systems are treated. The algorithm we propose also demonstrates quite satisfactory resistance to projection data noise that is inherent in tomography of strongly absorbing media.

Вестник ЮУрГУ, Серия "Образование, здравоохранение, физическая культура", 2006

Imaging in X-pinch rays produces records of several superimposed components of an object image fr... more Imaging in X-pinch rays produces records of several superimposed components of an object image from several radiation focuses separated in space. The present paper studies the feasibility of restoring an arbitrary chosen true component through the removal of the non-true one by the example of two experimental images with two superimposed components. The generalized discrete blurring model and iterative restoration algorithm used are described. It is shown that standard boundary conditions give satisfactory results for “Ant” image but “Pinch” image requires a special image extrapolation approach based on the fitting of reflection direction relative to the boundary for each reproduced structure.

Proceedings of the 38th Progress In Electromagnetics Research Symposium, 2017

The main problem in diffuse optical tomography is too low spatial resolution due to the multiple ... more The main problem in diffuse optical tomography is too low spatial resolution due to the multiple scattering of light. For solving this problem we have recently proposed a perturbation model that uses the early arriving diffuse photons for reconstructing the local disturbances of absorbing and diffusion coefficients. In the paper we develop our approach and derive an analytical representation of the sensitivity functions, which model the imaging operator, for parallel-plate transmission geometry. We first derive analytical expressions for the case of a semi-infinite scattering medium by using Green's function of the non-stationary diffusion equation and then apply these expressions to evaluate the sensitivity functions for parallel-plate transmission geometry using an original method of equivalent inverse source. The efficiency of our approach is demonstrated through a numerical experiment wherein the absorbing and scattering inhomogeneities in a rectangular scattering phantom are recovered using an original hybrid algorithm which combines the algebraic reconstruction technique with regularization via total variation norm minimization. It is shown that the transverse resolution as well as the longitudinal one can be better than 4 mm inside a 8-cm-thick phantom.

Квантовая электроника, 2014

Предложен новый метод определения весовых функций для реконструкции поглощающих неоднородностей т... more Предложен новый метод определения весовых функций для реконструкции поглощающих неоднородностей тканей методом импульсной пертурбационной диффузионной оптической томографии, использующей трансмиссионную геометрию плоского слоя. В основе метода лежит аналитический подход к расчету весовых функций для полубесконечной рассеивающей среды и использование оригинального метода эквивалентного инверсного источника с целью получения весовых распределений для геометрии плоского слоя. Для оценки корректности предложенного метода расчета весовых функций поставлен численный эксперимент по реконструкции поглощающих неоднородностей. Показано, что пертурбационная модель реконструкции на основе предложенного метода расчета весовых функций позволяет разрешать в центре объекта толщиной 8 см неоднородности размером менее 0.3 см и ~0.4 см, расположенные соответственно в направлениях, поперечном и продольном направлению зондирующего излучения.

Вестник Южно Уральского Государственного Университета Серия Образование Здравоохранение Физическая Культура, 2006

Computer Optics, Sep 30, 2023

The paper presents an original approach to time-domain reflectance fluorescence molecular tomogra... more The paper presents an original approach to time-domain reflectance fluorescence molecular tomography (FMT) of small animals. It is based on the use of early arriving photons and state-of-the-art compressed-sensing-like reconstruction algorithms and aims to improve the spatial resolution of fluorescent images. We deduce the fundamental equation that models the imaging operator and derive analytical representations for the sensitivity functions which are responsible for the reconstruction of the fluorophore absorption coefficient. The idea of fluorescence lifetime tomography with our approach is also discussed. We conduct a numerical experiment on 3D reconstruction of box phantoms with spherical fluorescent inclusions of small diameters. For modeling measurement data and constructing the sensitivity matrix we assume a virtual fluorescence tomograph with a scanning fiber probe that illuminates and collects light in reflectance geometry. It provides for large source-receiver separations which correspond to the macroscopic regime. Two compressed-sensing-like reconstruction algorithms are used to solve the inverse problem. These are the algebraic reconstruction technique with total variation regularization and our modification of the fast iterative shrinkage-thresholding algorithm. Results of our numerical experiment show that our approach is capable of achieving as good spatial resolution as 0.2 mm and even better at depths to 9 mm inclusive.

Journal of Electronic Imaging, 2018

Abstract. The paper presents an original hybrid image reconstruction algorithm ART-TVS for few-vi... more Abstract. The paper presents an original hybrid image reconstruction algorithm ART-TVS for few-views computed tomography of strongly absorbing media. It is based on the well-known algebraic reconstruction technique (ART), regularization of interim results through minimization of the total variation norm (TV-regularization), and a method of adaptive segmentation, which is a modernization of the known region growing algorithm. It is shown that the ART-TVS algorithm does not give stripe artifacts even if the number of views is very small (eight or less). ART-TVS reconstruction results for two numerical models of metal shells are compared with those obtained with the ART-TV algorithm (ART with TV-regularization and without adaptive segmentation), the iterative Potts minimization algorithm (IPMA), and our MART-AP algorithm (multiplicative ART with a priori information) we developed earlier for few-views discrete tomography. It is shown that ART-TVS outperforms ART-TV and IPMA and is comparable with MART-AP in reconstruction accuracy. Also, ART-TVS converges markedly faster than IRMA in cases where strongly underdetermined systems are treated. The algorithm we propose also demonstrates quite satisfactory resistance to projection data noise that is inherent in tomography of strongly absorbing media.

Journal of Biomedical Optics

Significance: Fluorescence molecular lifetime tomography (FMLT) plays an increasingly important r... more Significance: Fluorescence molecular lifetime tomography (FMLT) plays an increasingly important role in experimental oncology. The article presents and experimentally verifies an original method of mesoscopic time domain FMLT, based on an asymptotic approximation to the fluorescence source function, which is valid for early arriving photons. Aim: The aim was to justify the efficiency of the method by experimental scanning and reconstruction of a phantom with a fluorophore. The experimental facility included the TCSPC system, the pulsed supercontinuum Fianium laser, and a three-channel fiber probe. Phantom scanning was done in mesoscopic regime for three-dimensional (3D) reflectance geometry. Approach: The sensitivity functions were simulated with a Monte Carlo method. A compressed-sensing-like reconstruction algorithm was used to solve the inverse problem for the fluorescence parameter distribution function, which included the fluorophore absorption coefficient and fluorescence lifetime distributions. The distributions were separated directly in the time domain with the QR-factorization least square method. Results: 3D tomograms of fluorescence parameters were obtained and analyzed using two strategies for the formation of measurement data arrays and sensitivity matrices. An algorithm is developed for the flexible choice of optimal strategy in view of attaining better reconstruction quality. Variants on how to improve the method are proposed, specifically, through stepped extraction and further use of a posteriori information about the object. Conclusions: Even if measurement data are limited, the proposed method is capable of giving adequate reconstructions but their quality depends on available a priori (or a posteriori) information. Further research aims to improve the method by implementing the variants proposed.

Journal of Biomedical Optics, 2022

Significance: Fluorescence molecular lifetime tomography (FMLT) plays an increasingly important r... more Significance: Fluorescence molecular lifetime tomography (FMLT) plays an increasingly important role in experimental oncology. The article presents and experimentally verifies an original method of mesoscopic time domain FMLT, based on an asymptotic approximation to the fluorescence source function, which is valid for early arriving photons. Aim: The aim was to justify the efficiency of the method by experimental scanning and reconstruction of a phantom with a fluorophore. The experimental facility included the TCSPC system, the pulsed supercontinuum Fianium laser, and a three-channel fiber probe. Phantom scanning was done in mesoscopic regime for three-dimensional (3D) reflectance geometry. Approach: The sensitivity functions were simulated with a Monte Carlo method. A compressed-sensing-like reconstruction algorithm was used to solve the inverse problem for the fluorescence parameter distribution function, which included the fluorophore absorption coefficient and fluorescence lifetime distributions. The distributions were separated directly in the time domain with the QR-factorization least square method. Results: 3D tomograms of fluorescence parameters were obtained and analyzed using two strategies for the formation of measurement data arrays and sensitivity matrices. An algorithm is developed for the flexible choice of optimal strategy in view of attaining better reconstruction quality. Variants on how to improve the method are proposed, specifically, through stepped extraction and further use of a posteriori information about the object. Conclusions: Even if measurement data are limited, the proposed method is capable of giving adequate reconstructions but their quality depends on available a priori (or a posteriori) information. Further research aims to improve the method by implementing the variants proposed.

Monte Carlo Methods and Applications, 2022

The paper describes a sensitivity function calculation method for few-view X-ray computed tomogra... more The paper describes a sensitivity function calculation method for few-view X-ray computed tomography of strongly absorbing objects. It is based on a probabilistic interpretation of energy transport through the object from a source to a detector. A PRIZMA code package is used to track photons. The code is developed at FSUE “RFNC–VNIITF named after Academ. E. I. Zababakhin” and implements a stochastic Monte Carlo method. The value of the sensitivity function in a discrete cell of the reconstruction region is assumed to be directly proportional to the fraction of photon trajectories which cross the cell from all those recorded by the detector. The method’s efficiency is validated through a numerical experiment on the reconstruction of a section of a spherical heavy-metal phantom with an air cavity and a density difference of 25 Ṫhe proposed method is shown to outperform the method based on projection approximation in case of reconstruction from 9 views.

Presentation at the 8th International Symposium on Optics and Biophotonics (Saratov, Russia, September 2020), 2020

One of the most effective approaches for improving the spatial resolution of fluorescent tomogram... more One of the most effective approaches for improving the spatial resolution of fluorescent tomograms is to apply the state-of-the-art reconstruction algorithms based on compressed sensing (CS) theory. The paper presents a numerical experiment on fluorescent image reconstruction where we compare two CS algorithms: the algebraic reconstruction technique (ART) with total variation regularization, ART-TV, and the ART with fast iterative shrinkage-thresholding, ART-FIST. For modeling measurement data and constructing the sensitivity matrix we assume a virtual fluorescence tomograph with a scanning fiber probe that illuminates and collects light in reflectance geometry with source-receiver separations corresponding to the macroscopic regime. We show that ART-FIST outperforms ART-TV in reproduction accuracy and is capable of achieving as good spatial resolution as 0.2 mm at depths to 9 mm inclusive, and is quite competitive in this sense with mesoscopic fluorescence tomography.

Presentation at the 4th International Symposium on Optics and Biophotonics, (Saratov, Russia, September 2016), 2016

The paper develops an original method of evaluating the weight functions for time-domain diffuse ... more The paper develops an original method of evaluating the weight functions for time-domain diffuse optical tomography in parallel-plate transmission geometry. We first derive analytical expressions for the case of a semi-infinite scattering medium by using Green’s function of the nonstationary diffusion equation. Then we assume that photon migration near the receiver on the opposite boundary can be similar in the cases of a semi-infinite space and a thick flat layer, find the positions of the equivalent and equivalent inverse sources inside the flat, and apply the formulas obtained to evaluate the weight functions for parallel-plate transmission geometry. The efficiency of our approach is demonstrated through a numerical experiment wherein the rectangular scattering phantoms with absorbing and scattering inhomogeneities are recovered using the hybrid method that combines algebraic reconstruction technique and total variation regularization.

Russian Journal of Nondestructive Testing

Digital tomosynthesis system (DTS) has been increasingly used in chest X-ray imaging with a limit... more Digital tomosynthesis system (DTS) has been increasingly used in chest X-ray imaging with a limited-projection angle image reconstruction method. Image reconstruction methods in chest digital tomosynthesis (CDT) have fundamental impacts on image characteristics. Among these methods, iterative algorithm provides the additional benefits of chest X-ray imaging. However, there is almost no research that maximum-likelihood expectationmaximization (MLEM) method in CDT system. Thus, the purpose of this study was (1) to develop MLEM reconstruction algorithm based on CDT system and (2) to quantitatively compare the image characteristics with respect to the total angular range and iteration number as applied this system. For that purpose, we performed both simulation using MATLAB program and experimental studies. Tomography was performed linearly with a maximum ±30 • total angular range and then we acquired Shepp-Logan and PMMA-Aluminum (Al) phantom images using 120 kVp X-ray source for simulation and experiment, respectively. We evaluated and compared the MLEM reconstructed image characteristics using root-mean-square error (RMSE) and signal difference-to-noise ratio (SDNR) with various total angular ranges and iteration numbers. According to the results, we can acquire improved image characteristics as the number of iterations and the number of projections increased. Also, we found optimized iteration number for 20 iteration numbers in our CDT system geometry because there were few changes of image characteristics over 20 iteration numbers. In conclusion, we have presented usefulness and effectiveness of developed CDT image reconstruction algorithm.

2012 5th International Symposium on Communications, Control and Signal Processing, 2012

The paper considers a new iterative algorithm for tomographic image reconstruction when a very li... more The paper considers a new iterative algorithm for tomographic image reconstruction when a very limited number of projections are registered. The algorithm uses a priori information on the discrete values of the object function to be reconstructed and is based on the known multiplicative algebraic reconstruction technique (MART). The new algorithm we called MART-AP organizes a cycle of “external” iterations where the image is corrected at each iteration, using the MART and an image mask synthesized with the help of a priori information. It has been shown in numerical experiment that the algorithm proposed helps completely remove streaklike artifacts usually present on the tomograms which were reconstructed in conditions of strongly incomplete data.

Computer Optics

Two algorithms of few-view tomography are compared, specifically, the iterative Potts minimizatio... more Two algorithms of few-view tomography are compared, specifically, the iterative Potts minimization algorithm (IPMA) and the algebraic reconstruction technique with TV-regularization and adaptive segmentation (ART-TVS). Both aim to reconstruct piecewise-constant structures, use the compressed sensing theory, and combine image reconstruction and segmentation procedures. Using a numerical experiment, it is shown that either algorithm can exactly reconstruct the Shepp-Logan phantom from as small as 7 views with noise characteristic of the medical applications of X-ray tomography. However, if an object has a complicated high-frequency structure (QR-code), the minimal number of views required for its exact reconstruction increases to 17–21 for ART-TVS and to 32–34 for IPMA. The ART-TVS algorithm developed by the authors is shown to outperform IPMA in reconstruction accuracy and speed and in resistance to abnormally high noise as well. ART-TVS holds good potential for further improvement.

International Journal for Numerical Methods in Biomedical Engineering, 2020

The paper presents an original approach to time-domain reflectance fluores-cence molecular tomogr... more The paper presents an original approach to time-domain reflectance fluores-cence molecular tomography (FMT) of small animals. It is based on the use of early arriving photons and state-of-the-art compressed-sensing-like reconstruction algorithms and aims to improve the spatial resolution of fluorescent images. We deduce the fundamental equation that models the imaging operator and derive analytical representations for the sensitivity functions which are responsible for the reconstruction of the fluorophore absorption coefficient. The idea of fluorescence lifetime tomography with our approach is also discussed. We conduct a numerical experiment on 3D reconstruction of box phantoms with spherical fluorescent inclusions of small diameters. For model-ing measurement data and constructing the sensitivity matrix we assume a virtual fluorescence tomograph with a scanning fiber probe that illuminates and collects light in reflectance geometry. It provides for large source-receiver separations which correspond to the macroscopic regime. Two compressed-sensing like reconstruction algorithms are used to solve the inverse problem. These are the algebraic reconstruction technique with total variation regularization and our modification of the fast iterative shrinkage-thresholding algorithm. Results of our numerical experiment show that our approach is capable of achieving as good spatial resolution as 0.2 mm and even better at depths to 9 mm inclusive.
K E Y W O R D S: early arriving photons, fluorescence molecular tomography, fluorescent inclusions, reconstruction algorithms, sensitivity functions, spatial resolution

Proceedings of SPIE, 2020

The paper is devoted to a new method of time-domain lifetime fluorescence molecular tomography. I... more The paper is devoted to a new method of time-domain lifetime fluorescence molecular tomography. It is based on the use of early arriving diffuse photons and original measurement data, which are determined for the individual time gates of the diffuse temporal responses for fluorescence and exiting radiation. The paper presents in short the theoretical foundation of the method and describes a numerical experiment on the separate reconstruction of fluorophore absorption coefficient and fluorescence lifetime for 3D reflectance geometry that is suitable for small animal imaging. We show our first reconstruction results for the 3D scattering object region 11x11x8 mm 3 in size with two spherical fluorescent inclusions 1 mm in diameter. The ways how to improve these results in the future are discussed.

Computer Optics, 2019

В статье сравниваются два алгоритма малоракурсной томографии: итерационный алго-ритм минимизации ... more В статье сравниваются два алгоритма малоракурсной томографии: итерационный алго-ритм минимизации функционала Поттса и алгебраический алгоритм реконструкции с TV-регуляризацией и адаптивной сегментацией. Оба алгоритма ориентированы на восстанов-ление кусочно-постоянных структур, используют теорию опознавания со сжатием и совме-щают процедуры реконструкции и сегментации изображений. На уровне численного экспе-римента показано, что каждый из алгоритмов способен точно восстанавливать фантом Шеппа-Логана всего по 7 ракурсам. Когда же речь идет о восстановлении объекта, имею-щего сложную высокочастотную структуру (QR-кода), минимальное число ракурсов, необ-ходимое для точной реконструкции, возрастает до 17-21 в случае алгоритма реконструкции с TV-регуляризацией и адаптивной сегментацией и до 32-34 в случае итерационного алго-ритма минимизации функционала Поттса. Показано, что разработанный авторами статьи алгоритм реконструкции с TV-регуляризацией и адаптивной сегментацией имеет некоторое преимущество над итерационным алгоритмом минимизации функционала Поттса по таким критериям, как точность и скорость реконструкции, а также устойчивость к шуму проекци-онных данных. Отмечено, что алгоритм реконструкции с TV-регуляризацией и адаптивной сегментацией имеет хороший потенциал для дальнейшего совершенствования.

Journal of Electronic Imaging, 2018

The paper presents an original hybrid image reconstruction algorithm ART-TVS for few-views comput... more The paper presents an original hybrid image reconstruction algorithm ART-TVS for few-views computed tomography of strongly absorbing media. It is based on the well-known algebraic reconstruction technique (ART), regularization of interim results through minimization of the total variation norm (TV-regularization), and a method of adaptive segmentation, which is a modernization of the known region growing algorithm. It is shown that the ART-TVS algorithm does not give stripe artifacts even if the number of views is very small (eight or less). ART-TVS reconstruction results for two numerical models of metal shells are compared with those obtained with the ART-TV algorithm (ART with TV-regularization and without adaptive segmentation), the iterative Potts minimization algorithm (IPMA), and our MART-AP algorithm (multiplicative ART with a priori information) we developed earlier for few-views discrete tomography. It is shown that ART-TVS outperforms ART-TV and IPMA and is
comparable with MART-AP in reconstruction accuracy. Also, ART-TVS converges markedly faster than IRMA in cases where strongly underdetermined systems are treated. The algorithm we propose also demonstrates quite satisfactory resistance to projection data noise that is inherent in tomography of strongly absorbing media.

Вестник ЮУрГУ, Серия "Образование, здравоохранение, физическая культура", 2006

Imaging in X-pinch rays produces records of several superimposed components of an object image fr... more Imaging in X-pinch rays produces records of several superimposed components of an object image from several radiation focuses separated in space. The present paper studies the feasibility of restoring an arbitrary chosen true component through the removal of the non-true one by the example of two experimental images with two superimposed components. The generalized discrete blurring model and iterative restoration algorithm used are described. It is shown that standard boundary conditions give satisfactory results for “Ant” image but “Pinch” image requires a special image extrapolation approach based on the fitting of reflection direction relative to the boundary for each reproduced structure.

Proceedings of the 38th Progress In Electromagnetics Research Symposium, 2017

The main problem in diffuse optical tomography is too low spatial resolution due to the multiple ... more The main problem in diffuse optical tomography is too low spatial resolution due to the multiple scattering of light. For solving this problem we have recently proposed a perturbation model that uses the early arriving diffuse photons for reconstructing the local disturbances of absorbing and diffusion coefficients. In the paper we develop our approach and derive an analytical representation of the sensitivity functions, which model the imaging operator, for parallel-plate transmission geometry. We first derive analytical expressions for the case of a semi-infinite scattering medium by using Green's function of the non-stationary diffusion equation and then apply these expressions to evaluate the sensitivity functions for parallel-plate transmission geometry using an original method of equivalent inverse source. The efficiency of our approach is demonstrated through a numerical experiment wherein the absorbing and scattering inhomogeneities in a rectangular scattering phantom are recovered using an original hybrid algorithm which combines the algebraic reconstruction technique with regularization via total variation norm minimization. It is shown that the transverse resolution as well as the longitudinal one can be better than 4 mm inside a 8-cm-thick phantom.

Квантовая электроника, 2014

Предложен новый метод определения весовых функций для реконструкции поглощающих неоднородностей т... more Предложен новый метод определения весовых функций для реконструкции поглощающих неоднородностей тканей методом импульсной пертурбационной диффузионной оптической томографии, использующей трансмиссионную геометрию плоского слоя. В основе метода лежит аналитический подход к расчету весовых функций для полубесконечной рассеивающей среды и использование оригинального метода эквивалентного инверсного источника с целью получения весовых распределений для геометрии плоского слоя. Для оценки корректности предложенного метода расчета весовых функций поставлен численный эксперимент по реконструкции поглощающих неоднородностей. Показано, что пертурбационная модель реконструкции на основе предложенного метода расчета весовых функций позволяет разрешать в центре объекта толщиной 8 см неоднородности размером менее 0.3 см и ~0.4 см, расположенные соответственно в направлениях, поперечном и продольном направлению зондирующего излучения.

Lambert Academic Publishing, 2014

В книге изложены принципы и проанализированы диагностические возможности диффузионной оптической ... more В книге изложены принципы и проанализированы диагностические возможности диффузионной оптической томографии тканей молочной железы. Проанализированы оптические свойства тканей груди, и на основе анализа разработаны ее оптические пространственные модели. В методологическом плане основное внимание уделено методу средних траекторий фотонов, приближенному методу импульсной диффузионной оптической томографии, позволяющему восстанавливать пространственные распределения оптических параметров в реальном масштабе времени. Изложены теоретические основы и рассмотрены вопросы алгоритмической реализации метода средних траекторий фотонов. Приведены примеры реконструкции и реставрации диффузионных томограмм численных моделей молочной железы для круговой, прямоугольной и конусной геометрий регистрации оптического сигнала. Дан количественный анализ точности воспроизведения структур на томограммах.
Книга может быть полезна для научных работников, инженеров-исследователей, преподавателей, аспирантов и студентов старших курсов, специализирующихся в области биомедицинской оптики, физики медицинской визуализации и обработки изображений.