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Dive into the research topics where Alexei G. Nazarov is active.

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Featured researches published by Alexei G. Nazarov.


IEEE Transactions on Biomedical Engineering | 2001

Computational modeling of three-dimensional microwave tomography of breast cancer

Alexander E. Bulyshev; Serguei Y. Semenov; Alexander E. Souvorov; Robert H. Svenson; Alexei G. Nazarov; Yuri E. Sizov; George P. Tatsis

The microwave tomographic approach is proposed to detect and image breast cancers. Taking into account the big difference in dielectrical properties between normal and malignant tissues, the authors have proposed using the microwave tomographic method to image a human breast. Because of the anatomical features of the objects, this case has to be referred to the tomography with a limited angle of observation. As a result of computer experiments the authors have established that multiview cylindrical configurations are able to provide microwave tomograms of the breast with a small size tumor inside. Using the gradient method, the authors have developed a computer code to create images of the three-dimensional objects in dielectrical properties on microwave frequencies.


IEEE Transactions on Biomedical Engineering | 2002

Three-dimensional microwave tomography: initial experimental imaging of animals

Serguei Y. Semenov; Robert H. Svenson; Alexander E. Bulyshev; Alexander E. Souvorov; Alexei G. Nazarov; Yuri E. Sizov; Vitaly G. Posukh; Andrey Pavlovsky; Pavel N. Repin; Andrey N. Starostin; Boris A. Voinov; Michael Taran; George P. Tatsis; Vladimir Y. Baranov

The purpose of this study was to construct a microwave tomographic system capable of conducting experiments with whole scale biological objects and to demonstrate the feasibility of microwave tomography for imaging such objects using a canine model. Experiments were conducted using a three-dimensional (3-D) microwave tomographic system with working chamber dimensions of 120 cm in diameter and 135 cm in height. The operating frequency was 0.9 GHz. The object under study was located in the central area of the tomographic chamber filled with a salt solution. Experimentally measured attenuation of the electromagnetic field through the thorax was about -120 dB. To obtain images, we used various two-dimensional and 3-D reconstruction schemes. Images of the canine were obtained. In spite of imperfections, the images represent a significant milestone in the development of microwave tomography for whole body imaging and demonstrate its feasibility.


IEEE Transactions on Biomedical Engineering | 1999

Three-dimensional microwave tomography: experimental prototype of the system and vector Born reconstruction method

Serguei Y. Semenov; Robert H. Svenson; Alexander E. Bulyshev; Alexander E. Souvorov; Alexei G. Nazarov; Yuri E. Sizov; Andrey Pavlovsky; Vladimir Y. Borisov; Boris A. Voinov; G. I. Simonova; Andrey N. Starostin; Vitaly G. Posukh; George P. Tatsis; Vladimir Y. Baranov

A method of image reconstruction in three-dimensional (3-D) microwave tomography in a weak dielectric contrast case has been developed. By utilizing only one component of the vector electromagnetic field this method allows successful reconstruction of images of 3-D mathematical phantoms, a prototype of the 3-D microwave tomographic system capable of imaging 3-D objects has been constructed. The system operates at a frequency of 2.36 GHz and utilizes a code-division technique. With dimensions of the cylindrical working chamber z=40 cm and d=60 cm, the system allows measurement of an attenuation up to 120 dB having signal-to-noise ratio about 30 dB. The direct problem solutions for different mathematical approaches were compared with an experimentally measured field distribution inside the working chamber. The tomographic system and the reconstruction method were tested in simple experimental imaging.


IEEE Transactions on Microwave Theory and Techniques | 1998

Microwave tomography: a two-dimensional Newton iterative scheme

A.E. Souvorov; Alexander E. Bulyshev; Serguei Y. Semenov; Robert H. Svenson; Alexei G. Nazarov; Yuri E. Sizov; George P. Tatsis

In this paper, a variant of the Newton method, which uses a fast solution of the direct problem and a dual mesh, is proposed. Computational and physical experiments with simple two-dimensional high-contrast phantoms are discussed, and a full-scaled image of a two-dimensional mathematical model of a human torso is obtained.


Inverse Problems | 2000

Three-dimensional microwave tomography. Theory and computer experiments in scalar approximation

Alexander E. Bulyshev; A.E. Souvorov; Serguei Y. Semenov; Robert H. Svenson; Alexei G. Nazarov; Yuri E. Sizov; George P. Tatsis

The results of computer simulated experiments in three-dimensional microwave tomography in scalar approximation are presented. The gradient method is employed to solve three-dimensional high-contrast microwave tomographic problems. A computer model for full-scale three-dimensional imaging has been created. Three-dimensional tomographic images of mathematical models of the human torso were obtained. Significant differences between two-dimensional and three-dimensional cases are emphasized. Some illumination schemes which can be applied in the three-dimensional case are discussed. A dependence of image quality on the number of vertically placed transmitters has been demonstrated. The computer simulation showed that three-dimensional full-scale human torso dielectrical properties images can be produced with acceptable computational time.


IEEE Transactions on Microwave Theory and Techniques | 2000

Spatial resolution of microwave tomography for detection of myocardial ischemia and infarction-experimental study on two-dimensional models

Serguei Y. Semenov; Robert H. Svenson; Alexander E. Bulyshev; Alexander E. Souvorov; Alexei G. Nazarov; Yuri E. Sizov; Vitaly G. Posukh; Andrey Pavlovsky; Pavel N. Repin; George P. Tatsis

An experimental study of spatial resolution of microwave tomography was performed. Our microwave tomographic system with operational frequencies of 0.9 and 2.36 GHz and with signal-to-noise ratio of 30 dB allowed us to achieve a spatial resolution between 7.3-9.5 mm and 6.3-7.8 mm at the former and latter frequencies, respectively. It was shown in experiments, with structurally complicated objects, that spatial resolutions of about the same distances can be expected in a practical application of microwave tomography to detect areas of myocardial ischemia and infarction.


IEEE Transactions on Microwave Theory and Techniques | 2000

Three-dimensional microwave tomography: experimental imaging of phantoms and biological objects

Serguei Y. Semenov; Alexander E. Bulyshev; A.E. Souvorov; Alexei G. Nazarov; Yuri E. Sizov; Robert H. Svenson; Vitaly G. Posukh; Andrey Pavlovsky; Pavel N. Repin; George P. Tatsis

Microwave tomographic experiments have been performed on a three-dimensional (3-D) phantom and excised canine heart using a 3-D system operating at frequency of 2.4 GHz. A modified gradient reconstruction approach has been employed for the 3-D image reconstruction. To compare two-dimensional (2-D) and 3-D approaches, we also performed 2-D image reconstruction using an approach based on the Newton method. Experimental data acquired on experimental phantoms were analyzed using both 2-D and 3-D reconstruction approaches. High-quality images were reconstructed using the 3-D approach. The reconstruction procedure failed when the 2-D approach was applied to reconstruct images of the 3-D object. An image of the dielectric properties of the excised canine heart was obtained using a 3-D reconstruction approach. Images successfully revealed a complex internal structure of the heart, including both right-hand side and left-hand side ventricles.


IEEE Transactions on Microwave Theory and Techniques | 1998

Microwave tomography: theoretical and experimental investigation of the iteration reconstruction algorithm

Serguei Y. Semenov; Alexander E. Bulyshev; A.E. Souvorov; Robert H. Svenson; Yuri E. Sizov; V.Y. Vorisov; Vitaly G. Posukh; I.M. Kozlov; Alexei G. Nazarov; George P. Tatsis

Results of experiments on the two-dimensional (2-D) quasi real-time microwave tomographic system have been reported. Various reconstruction possibilities of this system have been demonstrated on phantoms and canine hearts. The early utilized Rytov approximation is appropriate for low-contrast inverse problems. A new iterative reconstruction algorithm is proposed in this paper. The iterations converge to an accurate solution of the scalar Helmholtz-equation inverse problem in the case of higher contrasts. The goal of the reported study is an experimental and theoretical investigation of the proposed iteration algorithm. The influence on the quality of the reconstructed images and on the spatial resolution of such factors as the number of receivers, the accuracy of the scattered field measurements, and the dielectric contrast have been investigated.


Physics in Medicine and Biology | 2011

Microwave tomography of extremities: 1. Dedicated 2D system and physiological signatures.

Serguei Y. Semenov; James F. Kellam; Yuri E. Sizov; Alexei G. Nazarov; Thomas Williams; Bindu Nair; Andrey Pavlovsky; Vitaly G. Posukh; Michael Quinn

Microwave tomography (MWT) is a novel imaging modality which might be applicable for non-invasive assessment of functional and pathological conditions of biological tissues. Imaging of the soft tissue of extremities is one of its potential applications. The feasibility of this technology for such applications was demonstrated earlier. This is the first of two companion papers focused on an application of MWT for imaging of the extremitys soft tissues. The goal of this study is to assess the technical performance of the developed 2D MWT system dedicated for imaging of functional and pathological conditions of the extremitys soft tissues. Specifically, the systems performance was tested by its ability to detect signals associated with physiological activity and soft tissue interventions (circulatory related changes, blood flow reduction and a simulated compartmental syndrome)--the so-called physiological signatures. The developed 2D MWT system dedicated to the imaging of animal extremities demonstrates good technical performance allowing for stable and predictable data acquisition with reasonable agreement between the experimentally measured electromagnetic (EM) field and the simulated EM field within a measurement domain. Using the system, we were able to obtain physiological signatures associated with systolic versus diastolic phases of circulation in an animal extremity, reperfusion versus occlusion phases of the blood supply to the animals extremity and a compartment syndrome. The imaging results are presented and discussed in the second companion paper.


Physics in Medicine and Biology | 2011

Microwave tomography of extremities: 2. Functional fused imaging of flow reduction and simulated compartment syndrome

Serguei Y. Semenov; James F. Kellam; Bindu Nair; Thomas Williams; Michael Quinn; Yuri E. Sizov; Alexei G. Nazarov; Andrey Pavlovsky

Medical imaging has recently expanded into the dual- or multi-modality fusion of anatomical and functional imaging modalities. This significantly improves the diagnostic power while simultaneously increasing the cost of already expensive medical devices or investigations and decreasing their mobility. We are introducing a novel imaging concept of four-dimensional (4D) microwave tomographic (MWT) functional imaging: three dimensional (3D) in the spatial domain plus one dimensional (1D) in the time, functional dynamic domain. Instead of a fusion of images obtained by different imaging modalities, 4D MWT fuses absolute anatomical images with dynamic, differential images of the same imaging technology. The approach was successively validated in animal experiments with short-term arterial flow reduction and a simulated compartment syndrome in an initial simplified experimental setting using a dedicated MWT system. The presented fused images are not perfect as MWT is a novel imaging modality at its early stage of the development and ways of reading reconstructed MWT images need to be further studied and understood. However, the reconstructed fused images present clear evidence that microwave tomography is an emerging imaging modality with great potentials for functional imaging.

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A.E. Souvorov

Carolinas Medical Center

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