1,721,169 research outputs found
Sviluppo di un metodo ibrido analitico-FDTD per l’analisi della distribuzione di campo elettromagnetico in un ambiente chiuso
No full textInteraction between 3-T MRI systems and patients with an implanted pacemaker
No full textIn this paper, a transverse electro-magnetic
(TEM) coil operating at 128 MHz in a 3-T magnetic
resonance imaging system has been studied in terms of
the interaction with patients with or without an
implanted pacemaker. The pacemaker has been
simulated as a copper box with a catheter constituted by
an insulated copper wire with an uncapped tip and it has
been placed inside either box or anatomical models of
the thorax. Electromagnetic and thermal simulations
have been performed by using finite difference time
domain codes. The obtained results show that in the
absence of the pacemaker, and for a radiated power
producing in the box a whole body specific absorption
rate (SAR) of 1 W/kg, that is a typical value for MRI
examinations, the coil produces in the anatomical
models peak temperature values lower than the limits
issued by the International Electrotechnical
Commission (IEC). In the presence of the pacemaker,
temperature increments at the catheter tip in excess of
those issued by the IEC standard are obtained when the
MRI scanned area involves the pacemaker region. The
3-T coil produces lower SAR and temperature
increments with respect to a 64-MHz (1.5-T system)
birdcage antenna in patients with implanted pacemaker
Implementation of the Newton-Raphson and admittance methods for EIT
No full textElectrical Impedance Tomography (EIT) is an imaging technique which aims to the reconstruction of the spatial electrical conductivity distribution of a section of the human body. In this paper, in order to solve the EIT forward and inverse problems, a finite difference approach to the solution of Maxwell’s equations, namely the admittance method, and the Newton-Raphson algorithm have been employed, respectively. The Jacobian matrix involved in the Newton-Raphson (N&R) algorithm has been computed by using both the admittance matrix of the forward problem and the socalled sensitivity matrix. The reconstruction problem has been solved using the standard Tikhonov
regularization with various choices of the regularization matrix. The obtained results, for three thorax models of increasing complexity, approximating a section of the human chest, show that the lowest reconstruction errors are usually obtained by choosing as regularization matrix a discrete form of the Laplacian operator
Comparisons among EIT data collection techniques and reconstruction algorithms
No full textElectrical Impedance Tomography (EIT) is an imaging technique that aims to reconstruct the spatial electrical conductivity distribution in sections of the human body. In this paper, in order to solve the EIT forward and inverse problems, a finite difference approach to the solution of Maxwell’s equations and the Newton-Raphson algorithm have been employed, respectively. In particular, the inverse problem has been solved using the Tikhonov regularization with various choices of the regularization matrix. Moreover, different data collection methods have been tested on simulated measurements. The obtained results have been compared based on the average deviation of the estimated conductivity distribution with respect to the reference one. The reconstruction procedure has been validated through a comparison with the EIDORS open source software. The best image reconstruction has been obtained by using the neighboring data collection method with null regularization matrix, and using the truncated singular value decomposition to perform the matrix inversion. Moreover, the cross and opposite data collection methods showed better performance than the neighboring one in the presence of a random noise added to the measured signal, while the opposite method evidenced the best results with respect to electrode positioning uncertainties
CubeSat satellite patch antenna designed with 3D printable materials. A numerical analysis
Full text linkThe paper presents a compact patch antenna system designed using 3D printable materials and compatible with any CubeSat satellite structure. Small satellites are transforming the space industry, allowing space access with an important cost reduction for satellite industries and a shorter plan development time compared to bulky satellites. Moreover, using additive manufacturing, it is possible to design specific system components, also with a complex geometry of the inner part, without material wasting. Furthermore, a key point of 3D printing is to allow to go from design to construction straight, having an enormous effect on the supply chain. Generally, CubeSats count on Very High Frequency and Ultra High Frequency communication systems for low bit-rate uplink and downlink. Instead, S-band is among the favourite choices for high bit rates since the frequency range 2.40-2.45 GHz is one of the International Telecommunication Union (ITU) amateur satellite frequency range. An S-band printed antenna system is designed in the present paper, considering the limitations on size and the weight of CubeSat standard. The antenna system is simulated with an electromagnetic CAD, using the polylactic acid as substrate, or polylactide, a thermoplastic polyester widely used in 3D printing
A PXI based system for electrical impedance tomography
No full textIn this paper, a PXI based system for electrical impedance tomography (EIT) will be presented. A virtual instrument based on the PXI platform is used to inject current and to acquire voltage data on a 16 electrode perspex phantom filled with saline or gelled solutions that mimic human body tissues. The admittance method is used for the solution of the direct problem and a modified Newton-Raphson algorithm is used for the image reconstruction. Experimental measurements have been performed on saline or gelled solutions to establish a link between the salt concentration and the solution conductivity. A set of measurements has been performed on phantoms simulating, at various levels of approximation, the human body anatomy. The results indicate that the proposed EIT system is efficient and accurate. Moreover its modular structure makes it possible to test various data collection protocols and inversion algorithms. © 2011 IEEE
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