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Proceedings ArticleDOI

Finite Element Modeling of scattered electromagnetic waves for stroke analysis

03 Jul 2013-Vol. 2013, pp 2404-2407
TL;DR: This paper investigates the possibility of diagnosing the type of stroke using Finite Element Analysis (FEA) and creates a simulated head phantom with stroke, created with its specifying material characteristics like electrical conductivity and relative permittivity.
Abstract: Stroke has become one of the leading causes of mortality worldwide and about 800 in every 100,000 people suffer from stroke each year. The occurrence of stroke is ranked third among the causes of acute death and first among the causes for neurological dysfunction. Currently, Neurological examinations followed by medical imaging with CT, MRI or Angiography are used to provide better identification of the location and the type of the stroke, however they are neither fast, cost-effective nor portable. Microwave technology has emerged to complement these modalities to diagnose stroke as it is sensitive to the differences between the distinct dielectric properties of the brain tissues and blood. This paper investigates the possibility of diagnosing the type of stroke using Finite Element Analysis (FEA). The object of interest is a simulated head phantom with stroke, created with its specifying material characteristics like electrical conductivity and relative permittivity. The phantom is then placed in an electromagnetic field generated by a dipole antenna radiating at 1 GHz. The FEM forward model solver computes the scattered electromagnetic field by finding the solution for the Maxwell's wave equation in the head volume. Subsequently the inverse scattering problem is solved using the Contrast Source Inversion (CSI) method to reconstruct the dielectric profile of the head phantom.
Citations
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Journal ArticleDOI
TL;DR: Through computer simulations, it is foreseen that MW imaging may efficiently be exploited to locate and differentiate two types of brain stroke by detecting abnormal tissues’ dielectric properties in a 3D realistic head model.
Abstract: In this paper, a detailed analysis of microwave (MW) scattering from a three-dimensional (3D) anthropomorphic human head model is presented. It is the first time that the finite-element method (FEM) has been deployed to study the MW scattering phenomenon of a 3D realistic head model for brain stroke detection. A major contribution of this paper is to add anatomically more realistic details to the human head model compared with the literature available to date. Using the MRI database, a 3D numerical head model was developed and segmented into 21 different types through a novel tissue-mapping scheme and a mixed-model approach. The heterogeneous and frequency-dispersive dielectric properties were assigned to brain tissues using the same mapping technique. To mimic the simulation set-up, an eight-elements antenna array around the head model was designed using dipole antennae. Two types of brain stroke (haemorrhagic and ischaemic) at various locations inside the head model were then analysed for possible detection and classification. The transmitted and backscattered signals were calculated by finding out the solution of the Helmholtz wave equation in the frequency domain using the FEM. FE mesh convergence analysis for electric field values and comparison between different types of iterative solver were also performed to obtain error-free results in minimal computational time. At the end, specific absorption rate analysis was conducted to examine the ionization effects of MW signals to a 3D human head model. Through computer simulations, it is foreseen that MW imaging may efficiently be exploited to locate and differentiate two types of brain stroke by detecting abnormal tissues' dielectric properties. A significant contrast between electric field values of the normal and stroke-affected brain tissues was observed at the stroke location. This is a step towards generating MW scattering information for the development of an efficient image reconstruction algorithm.

14 citations


Cites background or methods from "Finite Element Modeling of scattere..."

  • ...Priyadarshini and Rajkumar [27] applied a FEM–CSI methodology on a four-layered ellipsoid head model to explore the MW scattering phenomenon for brain stroke detection of both types....

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  • ...4 rsos.royalsocietypublishing.org R.Soc.opensci.5:180319 ................................................ Priyadarshini and Rajkumar [27] applied a FEM–CSI methodology on a four-layered ellipsoid head model to explore the MW scattering phenomenon for brain stroke detection of both types....

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  • ...In this study, the dipole antenna was designed for a 1 GHz centre frequency because this value is reported as the most suitable frequency by the literature to date for the design of an effective MW head-imaging system [14,23,25,27,35,38,40,42]....

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  • ...This is because 1 GHz is the most appropriate frequency for a MW head-imaging system, suggested by the previously referenced literature [14,23,25,27,35,38,40,42] and the evaluations we made during our research [43–45]....

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  • ...Priyadarshini N, Rajkumar E. 2013 Finite element modeling of scattered electromagnetic waves for stroke analysis....

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Journal ArticleDOI
21 Nov 2017-PeerJ
TL;DR: It is seen from this study that the microwave imaging may effectively be utilized for the detection, localization and differentiation of different types of brain stroke and it is suggested after careful study of various inversion methods in practice for microwave head imaging, that the contrast source inversion method may be more suitable and computationally efficient for such problems.
Abstract: In this paper, we have presented a microwave scattering analysis from multiple human head models. This study incorporates different levels of detail in the human head models and its effect on microwave scattering phenomenon. Two levels of detail are taken into account; (i) Simplified ellipse shaped head model (ii) Anatomically realistic head model, implemented using 2-D geometry. In addition, heterogenic and frequency-dispersive behavior of the brain tissues has also been incorporated in our head models. It is identified during this study that the microwave scattering phenomenon changes significantly once the complexity of head model is increased by incorporating more details using magnetic resonance imaging database. It is also found out that the microwave scattering results match in both types of head model (i.e., geometrically simple and anatomically realistic), once the measurements are made in the structurally simplified regions. However, the results diverge considerably in the complex areas of brain due to the arbitrary shape interface of tissue layers in the anatomically realistic head model. After incorporating various levels of detail, the solution of subject microwave scattering problem and the measurement of transmitted and backscattered signals were obtained using finite element method. Mesh convergence analysis was also performed to achieve error free results with a minimum number of mesh elements and a lesser degree of freedom in the fast computational time. The results were promising and the E-Field values converged for both simple and complex geometrical models. However, the E-Field difference between both types of head model at the same reference point differentiated a lot in terms of magnitude. At complex location, a high difference value of 0.04236 V/m was measured compared to the simple location, where it turned out to be 0.00197 V/m. This study also contributes to provide a comparison analysis between the direct and iterative solvers so as to find out the solution of subject microwave scattering problem in a minimum computational time along with memory resources requirement. It is seen from this study that the microwave imaging may effectively be utilized for the detection, localization and differentiation of different types of brain stroke. The simulation results verified that the microwave imaging can be efficiently exploited to study the significant contrast between electric field values of the normal and abnormal brain tissues for the investigation of brain anomalies. In the end, a specific absorption rate analysis was carried out to compare the ionizing effects of microwave signals to different types of head model using a factor of safety for brain tissues. It is also suggested after careful study of various inversion methods in practice for microwave head imaging, that the contrast source inversion method may be more suitable and computationally efficient for such problems.

12 citations


Cites background from "Finite Element Modeling of scattere..."

  • ...In the same year, (Priyadarshini & Rajkumar, 2013) performed computer simulations to study the electromagnetic (EM) waves scattering phenomenon by an ellipsoid head model for brain stroke analysis....

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Journal ArticleDOI
TL;DR: A comparison of microwave signals scattering from an anatomically realistic human head model in the presence and absence of brain stroke is presented and the interaction between microwave signals and the multilayer structure of head is studied.
Abstract: Brain stroke incidences have arisen at an alarming rate over the past few decades. These strokes are not only life threatening, but also bring with them a very poor prognosis. There is a need to investigate the onset of stroke symptoms in a matter of few hours by the doctor. To address this, Electromagnetic Impedance Tomography (EMIT) employing microwave imaging technique is an emerging, cost-effective and portable brain stroke diagnostic modality. It has the potential for rapid stroke detection, classification and continuous brain monitoring. EMIT can supplement current brain imaging and diagnostic tools (CT, MRI or PET) due to its safe, non-ionizing and non-invasive features. It relies on the significant contrast between dielectric properties of the normal and abnormal brain tissues. In this paper, a comparison of microwave signals scattering from an anatomically realistic human head model in the presence and absence of brain stroke is presented. The head model also incorporates the heterogenic and frequency-dispersive behavior of brain tissues for the simulation setup. To study the interaction between microwave signals and the multilayer structure of head, a forward model has been formulated and evaluated using Finite Element Method (FEM). Specific Absorption Rate (SAR) analysis is also performed to comply with safety limits of the transmitted signals for minimum ionizing effects to brain tissues, while ensuring maximum signal penetration into the head.

9 citations


Cites methods from "Finite Element Modeling of scattere..."

  • ...In the same year, Priyadarshini and Rajkumar [25] performed an EM waves scattering analysis for brain stroke diagnostics using FEM-CSI methodology but on a simplified ellipsoid head model....

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Proceedings ArticleDOI
03 Jul 2013
TL;DR: A simultaneous analysis system for blood pressure and flow using photoplethysmography and ultrasonic-measurement-integrated simulation is developed and confirmed by analysis of blood flow field in a carotid artery and corresponding wave intensity values.
Abstract: We developed a simultaneous analysis system for blood pressure and flow using photoplethysmography and ultrasonic-measurement-integrated simulation. The validity of the system was confirmed by analysis of blood flow field in a carotid artery and corresponding wave intensity (WI) values.

4 citations

Journal ArticleDOI
TL;DR: The initial results obtained in this research indicates that EMIT-based head imaging system has a potential for rapid stroke detection, classification, and continuous brain monitoring and offers a comparatively cost-effective solution.
Abstract: The objective of this research is to investigate the feasibility of Electromagnetic based Impedance Tomography (EMIT) for brain stroke detection, localization and classification. Electromagnetic based Impedance Tomography employing microwave imaging technique is an emerging brain stroke diagnostic modality. It relies on the significant contrast between dielectric properties of the normal and abnormal brain tissues. To study the interaction between micro-wave signals and head tissues, the simulations are performed using a geometrically simple 3-D ellipsoid head model with emulated stroke. Finite Element numerical technique is adopted to find the solution of Maxwell’s equations to measure the transmitted and backscattered signals in forward problem. Contrast Source Inversion technique is proposed to solve the inverse scattering problem and reconstruct brain images based on calculated dielectric profiles. Detailed analysis is performed to determine the safety limits of transmitted signals to minimize ionizing effects while ensuring maximum penetration. The simulations verify the inhomogeneous and frequency-dispersive behavior of brain tissue’s dielectric properties. The solution of the forward problem demonstrates the microwave signals scattering by the multilayer structure of the head model, duly validated by analytical results. The scattering phenomena can be fully capitalized by image reconstruction algorithm to obtain brain images and detect stroke presence. The initial results obtained in this research and prior work indicates that EMIT-based head imaging system has a potential for rapid stroke detection, classification, and continuous brain monitoring and offers a comparatively cost-effective solution.

2 citations


Cites methods from "Finite Element Modeling of scattere..."

  • ...An investigation through Finite Element Analysis (FEA), for the possibility of diagnosing the types of brain stroke using microwave imaging system (1 GHz), was carried out in 2013 by Priyadarshini and Rajkumar [34]....

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References
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Journal ArticleDOI
TL;DR: It is suggested that multifrequency MWT has the potential to significantly improve imaging results and is assessed as a novel imaging modality with particular focus on stroke detection.
Abstract: There is a need for a medical imaging technology, that supplements current clinical brain imaging techniques, for the near-patient and mobile assessment of cerebral vascular disease. Microwave tomography (MWT) is a novel imaging modality that has this potential. The aim of the study was to assess the feasibility, and potential performance characteristics, of MWT for brain imaging with particular focus on stroke detection. The study was conducted using MWT computer simulations and 2D head model with stroke. A nonlinear Newton reconstruction approach was used. The MWT imaging of deep brain tissues presents a significant challenge, as the brain is an object of interest that is located inside a high dielectric contrast shield, comprising the skull and CSF. However, high performance, nonlinear MWT inversion methods produced biologically meaningful images of the brain including images of stroke. It is suggested that multifrequency MWT has the potential to significantly improve imaging results.

231 citations


"Finite Element Modeling of scattere..." refers background in this paper

  • ...From [5] the attenuation was found to be very high between 1GHz to 2GHz and hence a frequency between 0....

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  • ...permittivity ( r) for the different layers of the normal head at 1 GHz are got from a published data [5,6] and are presented in Table 1....

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Journal ArticleDOI
TL;DR: A simple design tool is introduced to devise guidelines to properly set the working frequency as well as to choose the optimum matching medium to facilitate the penetration of the probing wave into the head.
Abstract: The adoption of microwave imaging as a tool for non- invasive monitoring of brain stroke has recently gained increasing attention. In this respect, the paper aims at providing a twofold contribution. First, we introduce a simple design tool to devise guidelines to properly set the working frequency as well as to choose the optimum matching medium needed to facilitate the penetration of the probing wave into the head. Second, we propose an imaging strategy based on a modifled formulation of the linear sampling method, which allows a quasi real time monitoring of the disease's evolution. The accuracy of the design guidelines and performance of the imaging strategy are assessed through numerical examples dealing with 2D anthropomorphic phantoms.

227 citations


"Finite Element Modeling of scattere..." refers background in this paper

  • ...The three major advantages of MWT over the existing modalities are, one being able to perform continuous monitoring as microwaves are non ionizing radiations unlike CT, the second being the property of the affected tissue showing variation in its dielectric values from the healthy tissues and the third being portable and cost effectiveness of the design [3]....

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Journal ArticleDOI
TL;DR: In this paper, the performance of the Newton and the multiplicative regularized contrast source inversion (MR-CSI) methods in 2D geometry and gradient and MR-CSIs in 3D geometry using high-contrast, medium-size phantoms, and biological objects was evaluated and discussed based on its performance and quality of reconstructed images.
Abstract: Microwave tomography is an imaging modality based on differentiation of dielectric properties of an object. The dielectric properties of biological tissues and its functional changes have high medical significance. Biomedical applications of microwave tomography are a very complicated and challenging problem, from both technical and image reconstruction point-of-views. The high contrast in tissue dielectric properties presenting significant advantage for diagnostic purposes possesses a very challenging problem from an image-reconstruction prospective. Different imaging approaches have been developed to attack the problem, such as two-dimensional (2-D) and three-dimensional (3-D), minimization, and iteration schemes. The goal of this research is to study imaging performance of the Newton and the multiplicative regularized contrast source inversion (MR-CSI) methods in 2-D geometry and gradient and MR-CSI methods in 3-D geometry using high-contrast, medium-size phantoms, and biological objects. Experiments were conducted on phantoms and excised segment of a pig hind-leg using a 3-D microwave-tomographic system operating at frequencies of 0.9 and 2.05 GHz. Both objects being of medium size (10-15 cm) possess high dielectric contrasts. Reconstructed images were obtained using all imaging approaches. Different approaches are evaluated and discussed based on its performance and quality of reconstructed images.

195 citations

Journal ArticleDOI
TL;DR: In this article, the authors derived a new inversion algorithm based on the contrast source inversion (CSI) algorithm and a finite element method (FEM) discretization of the Helmholtz differential operator formulation for the scattered electromagnetic field.
Abstract: With respect to the microwave imaging of the dielectric properties in an imaging region, the full derivation of a new inversion algorithm based on the contrast source inversion (CSI) algorithm and a finite-element method (FEM) discretization of the Helmholtz differential operator formulation for the scattered electromagnetic field is presented. The unknown dielectric properties are represented as nodal values on a two-dimensional (2D) arbitrary triangular mesh using linear basis functions. The use of FEM to represent the Helmholtz operator allows for the flexibility of having an inhomogeneous background medium, as well as the ability to accurately model any boundary shape or type: both conducting and absorbing. The resulting sparse and symmetric FEM matrix equation can be solved efficiently, and it is shown how its solution can be used to calculate the gradient operators required in the conjugate-gradient CSI update without storing the inverse of the FEM matrix. The inversion algorithm is applied to conductive-enclosures of various shapes and unbounded-region microwave tomography configurations where the 2D transverse magnetic (TM) approximation can be applied.

121 citations

Journal ArticleDOI
TL;DR: An algorithm for wide-band microwave imaging for the detection of a hemorrhagic stroke is proposed, using a realistic head phantom and finite-difference time-domain program to estimate back-scattered signals.
Abstract: This paper proposes an algorithm for wide-band microwave imaging for the detection of a hemorrhagic stroke. A realistic head phantom and finite-difference time-domain program are used to estimate back-scattered signals which are subsequently used in the image reconstruction process. The proposed imaging approach can lead to a portable and cost effective system; particularly suitable for rural medical clinics that lack the necessary resources in effective stroke diagnosing.

102 citations


"Finite Element Modeling of scattere..." refers background in this paper

  • ...MWT is based on the principle that the occurrence of stroke would create a pool of blood or clot with decreased oxygenation of the tissues that alter the dielectric properties of the tissues compared to that of the healthy brain [4]....

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