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Title: 3D BIOELECTROMAGNETIC COMPUTATION ON FINITE ELEMENTS
Abstract: Finite element computation of electric and magnetic fields induced in the body by noninvasive electromagnetic sources is discussed. Attention is focussed on three-dimensional calculations for full-scale body models with significant levels of internal anatomical structure. The finite element solution strategy including the sparse matrix approach which allows computation of over 100K degrees-of-freedom on standard reduced instruction set computer (RISC) workstation platforms is outlined. The finite element mesh generation problem is also described. Representative examples of the level of meshing detail and the type of 3D bioelectromagnetic solutions that can be achieved using finite elements in the workstation computing environment are shown. [Vol. 7, No. 2, pp. 9-25 (1992), Special Issue on Bioelectromagnetic Computations]
Author(s): Keith D. Paulsen, Xllin Jia, Daniel R. Lynch
File Type: Journal Paper
Issue:Volume: 7      Number: 2      Year: 1992
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Title: COMPUTATION OF THREE-DIMENSIONAL ELECTROMAGNETIC-FIELD DISTRIBUTIONS IN A HUMAN BODY USING THE WEAK FORM OF THE CGFFT METHOD
Abstract: The problem of the computation of electromagnetic-field distributions in a strongly inhomogeneous human body is formulated in terms of an integral equation over the body. A weak form of the integral equation is discussed, in which the spatial derivatives occurring in this equation are integrated analytically. The resulting equation can then be solved very efficiently using the advantageous combination of a conjugate-gradient iterative method and a fast Fourier technique (CGFFT). Numerical calculations have been carried out for a strongly inhomogeneous, lossy radially layered sphere. A comparison with the Mie-series solution shows that the present weak form of the CGFFT method yields accurate results. The absorbed power density inside a CAT-scan generated model of the body of one of the authors is computed. It demonstrates that the present method can be considered as a comparatively simple and efficient tool for solving electromagnetic wave- field problems in strongly inhomogeneous media. [Vol. 7, No. 2, pp. 26-42 (1992), Special lssue on Bioelectromagnetic Computations]
Author(s): A. Peter M. Zwamborn, Peter M. van den Berg, Jaap Mooibroek, Fred T. C. Koenis
File Type: Journal Paper
Issue:Volume: 7      Number: 2      Year: 1992
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Title: MULTIPLE MULTIPOLE METHOD APPLIED TO AN EXPOSURE SAFETY STUDY
Abstract: A summary of the three-dimensional implementation of the multiple multipole method (3D MMlP) is given, followed by discussions on the method's advantage and limitations on the basis of an example study. The advantages are seen in its quantitative validation capability, in its efficiency for smoothly shaped bodies and its achievable accuracy, in particular, near surfaces. However, MMP's greatest strength appears to be with problems with EM sources in the closest vicinity of lossy bodies. This is shown by a condensed presentation of a study investigating the RF exposure safety of UHF and VHF transmitters commonly used by radio and TV crews for onsite live reports. In addition to gaining knowledge about the locar SAR distribution, the goal of this study was to assess necessary safety distances for given threshold values. The presented study was performed with the 3D MMP software package on a 80386 based PC laptop extended by a 80860 board with 32MB RAM. [Vol.7, No.2, pp. 43-60 (1992), Special Issue on Bioelectromagnetic Computations]
Author(s): Niels Kuster
File Type: Journal Paper
Issue:Volume: 7      Number: 2      Year: 1992
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Title: APPLICATION OF NUMERICAL MODELING TECHNIQUES IN ELECTROMAGNETIC HYPERTHERMIA
Abstract: Electromagnetic hyperthermia has been demonstrated to be a safe and useful adjuvant to ionizing radiation in the treatment of malignant tumors. However, applicators and systems for delivering the optimum treatment prescribed by the physicians are far from being available at present. Computer modeling can play a significant role in the design of better heating equipment and in improving the quality of the hyperthermia treatments currently being administered. There is an active ongoing research to develop suitable calculational models using a variety of numerical techniques. But several gaps exist in the current knowledge regarding the validity of these numerical simulations in the clinical context. The development of treatment planning systems similar to those used for radiation therapy requires resolution of these issues. Of the different numerical modeling approaches currently being developed, the finite-difference time-domain (FD-TD) technique has been extensively applied to calculate specific absorption rate (SAR) patterns in complex 3-D heterogeneous biological objects primarily because it is accurate and has a small computer burden relative to frequency-domain integral equation and finite element techniques. Following a brief review of the historical development of numerical modeling of electromagnetic interaction with biological structures in the hyperthermia context, examples of recent calculations using FD-TD technique in realistic situations in electromagnetic hyperthermia are provided. It has been observed from 2-D calculations, that the water bolus, routinely used in the clinic to provide energy coupling and surface (skin) temperature control, and the inhomogeneous tissue structures significantly modify the SAR patterns compared to patterns computed in planar and homogeneous structures. In conclusion, future areas of work are identified and discussed. [Vol. 7, No. 2, pp. 61-71 (1992), Special lssue on Bioelectromagnetic Computations]
Author(s): V. Sathiaseelan, A. Taflovel, M.J. Picket-Mayl, C. Reuterl, B. B. Mittal
File Type: Journal Paper
Issue:Volume: 7      Number: 2      Year: 1992
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Title: ANALYSIS AND COMPUTATION OF LEAKY-WAVE HYPERTHERMIA APPLICATOR
Abstract: The use of electromagnetic waves to induce hyperthermia in cancer therapy has been the subject of intensive research but obtaining good resolution at depth in the abdomen and pelvic regions remains a fundamental problem. This paper investigates the prospects for generating leaky-waves in tissue to improve field penetration and focussing at depth. An approximate analysis based on a planar structure illustrates the feasibility of obtaining good resolution at depth but leaky-wave action in a strict sense is not possible. Measurements on an applicator conformal with the phantom tissue simulated by a saline solution, demonstrate good resolution and penetration but hotspot regions are detected around the launcher region. A three dimensional finite difference time domain (FDTD) computation is performed in Cartesian, circular cylindrical and elliptic cylindrical coordinates to model all the effects for various geometries of the phantom region and different launching symmetries. The results illustrate the need for symmetric launching of the strip, computational convergence and mode diagnostic data, the shape of the focal region and the useful property of being able to shift the focal region by changing frequency. It is concluded that this new quasi-leaky-wave applicator concept is potentially capable of giving improved focal resolution at depth with some positional control and only one generator is required. Optimising the launching of the quasi- leaky waves on the applicator and preventing hotspot regions from creating unwanted tissue heating are remaining practical problems to address. [Vol. 7, No. 2, pp. 72-84 (1992), Special Issue on Bioelectromagnetic Computations]
Author(s): J. R. James, G. Andrasic.
File Type: Journal Paper
Issue:Volume: 7      Number: 2      Year: 1992
Download Link:Click here to download PDF     File Size: 2500 KB

Title: EVALUATION OF CLINICAL HYPERTHERMIA TREATMENT USING TIME DOMAIN FINITE DIFFERENCE MODELLING TECHNIQUE
Abstract: The use of numerical modelling techniques, especially the time domain finite difference method, has improved the understanding of power deposition in human bodies undergoing cancer treatment with microwave or radiofrequency waves. In this paper, clinical hyperthermia treatments are modelled with the time domain finite difference method. quantitative assessment criteria are defined for the evaluation of computed power deposition patterns and are found to be useful in determining whether a particular treatment is likely to succeed. [Vol. 7, No. 2, pp. 85-96 (1992), Special Issue on Bioelectromagnetic Computations]
Author(s): H. C. Taylor, R. W. M. Lau
File Type: Journal Paper
Issue:Volume: 7      Number: 2      Year: 1992
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Title: OPTIMIZING PLANAR SOURCE DISTRIBUTIONS FOR DEEP POWER DEPOSITION IN BIOLOGICAL TISSUE
Abstract: In non-invasive hyperthermia, penetration depth in high water content biological tissue can be increased up to 3 times using a focused instead of uniform surface electric field distribution. The focusing involves maximizing the field integral at a focal point by solving for the surface phase function which makes the integrand real and positive for all surface points. The resulting non-linear differential equation is solved in using a series approximation. A focused power deposition pattern is presented using this ideal planar distribution which is the theoretical optimum for high resolution hyperthermia cancer treatment. [Vol. 7, No. 2, pp. 97- 109 (1992), Special Issue on Bioelectromagnetic Computations]
Author(s): Carey M. Rappaport
File Type: Journal Paper
Issue:Volume: 7      Number: 2      Year: 1992
Download Link:Click here to download PDF     File Size: 860 KB

Title: TWO-DIMENSIONAL TEMPERATURE RETRIEVAL IN BIOLOGICAL STRUCTURES BY MULTIFREQUENCY MICROWAVE RADIOMETRY: A SOBOLEV-SPACE SOLUTION
Abstract: The problem of retrieving a two-dimensional temperature distribution from radiometric data measured at various frequencies and for different positions of the sensing antenna around the body has been considered. The retrieval has been modelled as an inverse problem whose solution is investigated in a suitably defined functional space which takes regularity properties of temperature functions into account. The retrieval of hot spots in a cylinder at uniform temperature has been numerically analyzed, the examples being relevant in the hyperthermia treatment of malignancies. [Vol. 7, No. 2, pp. 110-120 (1992), Special Issue on Bioelectromagnetic Computations]
Author(s): Fernando Bardati, Valerie J. Brown, Piero Tognolatti
File Type: Journal Paper
Issue:Volume: 7      Number: 2      Year: 1992
Download Link:Click here to download PDF     File Size: 740 KB

Title: NON-INVASIVE ACTIVE THERMOMETRY WITH A MICROWAVE TOMOGRAPHIC SCANNER IN HYPERTHERMIA TREATMENTS
Abstract: In this work the active microwave tomographic imaging of tissue temperature changes induced in deep hyperthermia treatments is studied. The thermal images would allow to monitor and optimize the treatment, increasing its efficacy and avoiding the heating of healthy tissues. As some hyperthermia systems are based on a cylindrical geometry, it is possible to integrate a microwave imaging array in the same structure, providing a non-invasive tool for the monitoring and control. The application of this technique to deep hyperthermia treatments is investigated by numerical simulations and experimentally on two phantoms of thorax and pelvis, using a prototype for microwave tomography recently developed [Jofre et al, 1990]. lVol. 7, No. 2, pp. 121-127 (1992), Special Issue on Bioelectromagnetic Computations]
Author(s): J. J. Mallorqui, A. Broquetas, L. Jofre, A. Cardama
File Type: Journal Paper
Issue:Volume: 7      Number: 2      Year: 1992
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Title: ELECTRICAL IMPEDANCE TOMOGRAPHY IN THREE DIMENSIONS
Abstract: An algorithm is developed for electrical impedance tomography (EIT) of three-dimensional volumes using multi-planar electrode arrays. This algorithm is based upon the method of least squares, and uses one step of Newton's method to estimate the conductivity distribution inside the volume using electrical measurements made on the boundary. An implementation of the algorithm for right cylindrical volumes is described. This computer code, called N3D, permits reconstructions with up to 2016 degrees of freedom. The code uses an initial guess consisting of uniform conductivity, allowing many of the computations to be done analytically. Although the code does not reconstruct the conductivity distribution accurately (unless it differs very little from a constant), it does yield useful images at reasonable computational cost. The algorithm is demonstrated using three-dimensional resistivity distributions reconstructed from experimental data. [Vol. 7, No. 2, pp. 128-147 (1992), Special Issue on Bioelectromagnetic Computations]
Author(s): J. Goble, M. Cheney, D. Isaacson
File Type: Journal Paper
Issue:Volume: 7      Number: 2      Year: 1992
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Title: COMPUTATIONAL METHOD FOR POWER LINE MAGNETIC FIELD EVALUATION
Abstract: The paper reports a model for the power line magnetic field evaluation. The obtained results for three different power lines (380 kV double circuit,380 kV single circuit, 220 kV double circuit) was validated with measurement data. Calculated and corresponding measured data were found in good agreement. The influence of geometrical and electrical power line parameters, such as the spatial configuration of the conductors and line phase sequences, is evaluated and discussed. Data on the influence of adjacent line span on the field are also reported. The method can be used for prediction of human exposure in epidemiological studies. [Vol. 7, No. 2, pp. 148-161 (1992), Special Issue on Bioelectromagnetic Computations]
Author(s): Santi Tofani, Giovanni d'Amore, Giancarlo Bonazzola, Giovanni Fiandino
File Type: Journal Paper
Issue:Volume: 7      Number: 2      Year: 1992
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Title: SIMPLIFIED ANALYTICAL SOLUTIONS FOR MAGNETIC SIMULATION OF NEURONS
Abstract: Strong pulses of magnetic field are used to stimulate peripheral nerves and motor neurons in the cerebral cortex,. Such stimulation is used in neurology for numerous diagnostic purposes. The electric field induced in tissue along the neuron and its spatial derivative are the parameters determining neural response. Another important parameter influencing the efficiency of stimulation is the inductance of a coil producing the magnetic field, as it defines the current time derivative for a given pulse generator. For arbitrarily located coils of arbitrary shapes, a semi-analytical solution is presented to calculate spatial distributions of the electric field and its spatial derivatives in a semi-infinite tissue model. Analytical solutions are given for coils composed of linear segments parallel or perpendicular to the air- tissue interface. Expressions for inductance of coils having suitable geometries for neural stimulation are derived. Coils can be optimized for stimulation of nerves at given orientation and distance from the air-tissue interface. In the optimization, coil dimensions and shape are considered as they affect both the induced field and inductance. A quadruple coil consisting of triangular sections appears to offer some advantages over other shapes for stimulation of shallow nerves. For deep nerves spaces quadruple square and three-dimensional coils are preferred. Analyses described are useful in evaluating various options, gaining an insight into the physical phenomena involved, and as the first step before undertaking a numerical analysis of models more closely representing the tissue electrical and geometrical complexities. [Vol. 7, No. 2, pp. 162-178 (1992), Special Issue on Bioelectromagnetic Computations]
Author(s): Karu P. Esselle, Maria A. Stuchly
File Type: Journal Paper
Issue:Volume: 7      Number: 2      Year: 1992
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Title: ANALYSIS OF THE STIMULATION OF A NERVE FIBER SURROUNDED BY AN INHOMOGENEOUS~ ANISOTROPIC, AND DISPERSIVE TISSUE
Abstract: A method for evaluating the threshold for electric and magnetic stimulation of nerves surrounded by an inhomogeneous, anisotropic, and dispersive tissue has been developed. The scalar potential distribution induced by a given electric or magnetic source is evaluated by using the Finite Difference Technique. Calculations are perforrned with a FORTRAN code, and for non dispersive tissues a spread-sheet is also used. Nerve fiber excitation is described by using the FrankenhaeuserHuxley model in which the stimulating current density is obtained by extending the method proposed by Rattay. The analysis results predict that, with reference to the homogeneous case usually considered in literature, the larger differences in the current threshold are due to the tissue inhomogeneity, while the consideration of the dispersive properties of the tissues has less effect. [Vol. 7, No. 2, pp. 179-190 (1992), Special Issue on Bioelectromagnetic Computations]
Author(s): G. D'inzeo, S. Pisa, C. Giacomozzi
File Type: Journal Paper
Issue:Volume: 7      Number: 2      Year: 1992
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