Luca Zilberti

INRIM Istituto Nazionale di Ricerca Metrologica, Torino, Piedmont, Italy

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Publications (36)38.6 Total impact

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    ABSTRACT: The paper presents a computational study for the estimation of the temperature elevation occurring in a human subject carrying metallic hip prostheses when exposed to the magnetic field produced by gradient coils. The simulations are performed through validated numerical codes, which solve the electromagnetic and thermal equations applied to a high-resolution anatomical human model. Three different sets of gradient coils (traditional, split and uniplanar) are considered to evaluate the maximum steady-state temperature elevation in the human body. This result is then rescaled to take into account the waveform of the signal, the duty-cycle and the duration of the scan. Several exposure situations obtained by changing the patient's position are analyzed, finding temperature elevations on the order of some degrees. The results are of possible concern and provide evidence of the need for further specific investigations aimed at assuring the safety of potential patients carrying metallic hip implants. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 04/2015; DOI:10.1002/mrm.25687 · 3.40 Impact Factor
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    ABSTRACT: This paper investigates the influence of electrical and thermal human tissue parameters on the heating of a body illuminated by a millimeter plane electromagnetic wave. A stochastic approach is considered with a three-layer model of the body: it is found that the parameters of skin play a major role.
    IEEE Transactions on Magnetics 03/2015; 51(3):1-4. DOI:10.1109/TMAG.2014.2363898 · 1.21 Impact Factor
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    ABSTRACT: The thermal response of human tissues exposed to a focused beam terahertz electromagnetic radiation is evaluated through a combined analytical electromagnetic wave solution and a step-by-step finite element numerical model, which solves Pennes’ bioheat equation. The computational procedure is applied to a three-layer model of the human tissues for wave frequencies ranging from 0.025 THz to 1 THz and compared with a more detailed five-layer model. The effects of the Gaussian beam parameters of the electromagnetic radiation on the temperature elevation are finally evaluated.
    IEEE Transactions on Magnetics 03/2015; 51(3):1-4. DOI:10.1109/TMAG.2014.2355260 · 1.21 Impact Factor
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    ABSTRACT: A hybrid finite element–boundary element method, developed to solve eddy-current problems in the frequency domain, is applied to the electromagnetic analysis of voxel-based human models. A specific procedure employs a massively parallelized algorithm implemented on a multiple Graphic Processing Units (GPU) code to speed up the solution of large systems whose matrix exceeds the RAM capability. The database structure used for the electromagnetic problem is also suitable for a successive thermal analysis to evaluate the distribution of the temperature elevation due to the energy deposited by the waves in the tissues. Finally, some examples of application are presented.
    IEEE Transactions on Magnetics 03/2015; 51(3):1-4. DOI:10.1109/TMAG.2014.2363140 · 1.21 Impact Factor
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    ABSTRACT: This paper presents an overview of the recent research activities carried on at INRIM in the field of metrology for healthcare, aiming at supporting therapeutic and diagnostic techniques based on electromagnetics and nanomagnetics. Attention is here specifically focused on three research topics, respectively related to electromagnetic dosimetry for MR-safety, production and characterization of magnetic Ni80Fe20 nanodisks for biomedical applications and development of modeling tools to support the design of novel biosensors.
    Rendiconti Lincei. Scienze Fisiche e Naturali 01/2015; DOI:10.1007/s12210-015-0386-5 · 0.76 Impact Factor
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    ABSTRACT: This paper deals with the exposure of humans moving through the stray stationary magnetic field produced by magnetic resonance imaging scanners. In particular, the work evaluates the influence of the dielectric currents, whose effects have been disregarded up to now, despite the very high permittivity values obtained by extrapolation based on the most common dispersion models of tissue properties. The analysis is carried out by considering a high-resolution anatomical model through an original numerical procedure that includes the dielectric phenomena. The results prove that the high values of the dielectric permittivity produce limited, but nonnegligible variations on the induced current density, while weakly influencing the electric field. Finally, the stability of the results with respect to variations of the dielectric permittivity practically removes the need for an accurate measurement of such a parameter that is affected by high uncertainties at very low frequencies.
    IEEE Magnetics Letters 01/2015; 6:1-1. DOI:10.1109/LMAG.2015.2429641
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    ABSTRACT: The paper discusses the application of a hybrid Finite Element–Boundary Element technique to the electromagnetic dosimetric analysis of voxel based human models, with particular attention to the Magnetic Resonance Imaging appliances. A rational organization of the large amount of data involved by the voxel anatomy is presented to reduce the computational burden. The most suitable choice of the unknowns and the possible simplifying assumptions are also investigated. A hybrid Finite Element–Boundary Element approach is derived from the previous considerations, underlining the procedure for the system solution adopted when the whole algebraic matrix exceeds the RAM capabilities. The work is completed with some examples of applications.
    Engineering Analysis with Boundary Elements 12/2014; 49. DOI:10.1016/j.enganabound.2014.04.014 · 1.44 Impact Factor
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    ABSTRACT: This paper investigates the effect of relevant physical parameters on transient temperature elevation induced in human tissues by electromagnetic waves in the terahertz (THz) band. The problem is defined by assuming a plane wave, which, during a limited time interval, normally impinges on the surface of a 3-layer model of the human body, causing a thermal transient. The electromagnetic equations are solved analytically, while the thermal ones are handled according to the finite element method. A parametric analysis is performed with the aim of identifying the contribution of each parameter, showing that the properties of the first skin layer (except blood flow) play a major role in the computation of the maximum temperature rise for the considered exposure situation. Final results, obtained by combining all relevant parameters together, show that the deviation from the reference solution of the maximum temperature elevation in skin is included in the coverage intervals from -30% to +10% at 0.1 THz and from -33% to +18% at 1 THz (with 95% confidence level). These data allow bounding the possible temperature increase against the spread of tissue properties that could be reasonably used for dosimetric simulations. Bioelectromagnetics © 2014 Wiley Periodicals, Inc.
    Bioelectromagnetics 07/2014; 35(5). DOI:10.1002/bem.21842 · 1.86 Impact Factor
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    ABSTRACT: The electric current densities induced inside a human head by transcranial magnetic stimulations are evaluated through a hybrid finite-element–boundary-element method applied to an anatomical model based on voxel data set. The results of the computational procedure are first validated considering two model problems. Then, the induced E-field within the head of Duke model of the Virtual Family are simulated for two different transcranial magnetic stimulation coils, evaluating the impact of tissue properties variability and model resolution.
    IEEE Transactions on Magnetics 02/2014; 50(2):1033-1036. DOI:10.1109/TMAG.2013.2281739 · 1.21 Impact Factor
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    ABSTRACT: Boundary element and hybrid boundary element—finite element approaches are applied to the computation of induced electric field and specific absorption rate in voxel-based human models undergoing magnetic resonance imaging. Due to the very large size of the algebraic system, the procedure uses an iterative GMRES solver recalculating the element matrix at each iteration. A suitable processing of the Green integrals and a massively parallelized algorithm, based on the use of graphical processing units, leads to a strong reduction of the computational time.
    IEEE Transactions on Magnetics 02/2014; 50(2):1029-1032. DOI:10.1109/TMAG.2013.2280523 · 1.21 Impact Factor
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    ABSTRACT: The aim of this paper is the investigation of the numerical properties of the boundary element method (BEM) when applied to dosimetric analysis of human exposure to electromagnetic fields adopting high resolution voxel-based data sets. Some test problems are analyzed considering the neck region of the human body radiated by a loop antenna. Different strategies in the development of the problem equations are proposed and their effects on the conditioning of the BEM matrix are discussed. Several direct and iterative solvers are applied to the model problems and their efficiency is compared.
    IEEE Transactions on Magnetics 02/2014; 50(2):521-524. DOI:10.1109/TMAG.2013.2281215 · 1.21 Impact Factor
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    ABSTRACT: This paper presents and discusses a comparative numerical and experimental analysis of the electromagnetic (EM) phenomena arising in a laboratory phantom radiated by a radio-frequency field, simulating the exposure in a magnetic resonance imaging (MRI) context. A specific frequency-domain coupled finite element-boundary element solver, running in graphical processing unit environment, has been developed to analyze the EM effects as well in the presence of metallic objects simulating prosthetic implants. The experimental setup consists of an antenna radiating a cylindrical box filled with a tissue simulating liquid; a bulk metallic parallelepiped can be included to mimic the presence of a prosthesis.
    IEEE Transactions on Magnetics 01/2014; 50(11):1-4. DOI:10.1109/TMAG.2014.2323428 · 1.21 Impact Factor
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    ABSTRACT: This paper aims at evaluating the thermal effects produced by the gradient coils on patients carrying metallic hip prostheses when undergoing check-up in combined magnetic resonance imaging with a linear accelerator systems. The computations are performed by two noncommercial codes specifically developed by the authors for voxel based human models. The electromagnetic field problem is solved by a hybrid finite element-boundary element technique implemented in a massively parallelized GPU system. The temperature elevation due to the electromagnetic exposure is then evaluated through a finite element code. The computations are performed for a large number of situations, considering both radial and axial arrangements of the patient.
    IEEE Transactions on Magnetics 01/2014; 50(11):1-4. DOI:10.1109/TMAG.2014.2323119 · 1.21 Impact Factor
  • Luca Zilberti, Mario Chiampi
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    ABSTRACT: This paper deals with the electric field generated inside the bodies of people moving in proximity to magnetic resonance scanners. Different types of scanners (tubular and open) and various kinds of movements (translation, rotation, and revolution) are analyzed, considering the homogeneous human model proposed in some technical Standards. The computations are performed through the Boundary Element Method, adopting a reference frame attached to the body, which significantly reduces the computational burden. The induced electric fields are evaluated in terms of both spatial distributions and local time evolutions. The possibility of limiting the study to the head without affecting the accuracy of the results is also investigated. Finally, a first attempt to quantify the transient effect of charge separation is proposed.
    Health physics 12/2013; 105(6):498-511. DOI:10.1097/HP.0b013e31829b4aac · 0.77 Impact Factor
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    ABSTRACT: MRI-LINAC is a new image-guided radiotherapy treatment system that combines magnetic resonance imaging (MRI) and a linear particle accelerator (LINAC) into a single unit. Moving (i.e. rotating or translating) the patient inside the strong magnetic field of the split MRI-LINAC magnet can potentially induce high levels of electric fields and corresponding current densities in the conducting tissues. The prediction and assessment of patient safety in terms of electromagnetic field exposure has received very little attention for a split cylindrical MRI magnet configuration, especially in the vicinity of the gap region. In this novel numerical study, based on the quasi-static finite-difference (QSFD) method, rotation-induced electric fields and current densities are calculated considering a split 1 T magnet and a tissue-accurate 2 mm-resolution human body model. The patient was modelled in both axial and radial orientations relative to the magnet gap in a number of treatment/imaging scenarios. It was found that rotating the patient in the radial orientation produced an order of magnitude larger field exposure in the central nervous system than when the patient was rotated in the axial orientation. Also, rotating the patient with periods lower than about Trot = 43.3 s may result in field exposures above the limits set out in the international safety guidelines. The novel results of this investigation can provide useful insights into the safe use of the MRI-LINAC technology and optimal orientations of the patient during the treatment.
    IEEE transactions on bio-medical engineering 11/2013; 61(3). DOI:10.1109/TBME.2013.2289924 · 2.23 Impact Factor
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    ABSTRACT: This paper is focused on the uncertainty estimate of a hybrid experimental-numerical procedure for the evaluation of the electric field induced in a human model radiated by a low-frequency magnetic field produced by unknown sources. The procedure is based on magnetic field measurements in a limited number of points around the field source and makes use of the boundary element method. The uncertainty contribution due to the measurement operations is taken into account by evaluating its propagation through the computational process using a Monte Carlo approach coupled to a discrete numerical technique. The procedure is then applied to the case of a body exposed to the field generated by a Helmholtz coil system. The results show that the relative standard uncertainty of the estimated induced electric field is within a few percent.
    IEEE Transactions on Instrumentation and Measurement 06/2013; 62(6):1436-1442. DOI:10.1109/TIM.2012.2230812 · 1.71 Impact Factor
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    ABSTRACT: We investigated the efficiency in magnetic field mitigation of superimposed MgB2/Fe coaxial cups with cylindrical symmetry, subjected to an applied magnetic field parallel to their axis. The MgB2 cup was grown by a microwave-assisted Mg-liquid infiltration technique in a boron preform. This technique allows obtaining samples with a reduced amount of unreacted magnesium, shape chosen before the growth procedure, and easily scalable sizes. Local magnetic induction measurements were carried out by means of a cryogenic Hall probe mounted on a custom-designed stage moveable along the sample axis with micrometric resolution. The measurements were performed at 20 K and 30 K, in magnetic field up to 1.5 T, as a function of the external source field, of the position and of time. At higher magnetic fields the superposition of the Fe cup on the MgB2 one allows obtaining a shielding efficiency 3-4 times higher than that measured with the single superconducting cup. The magnetic induction relaxation rate is also strongly reduced. On the contrary, a decrease of the shielding efficiency of the hybrid system with respect to the MgB2 cup alone turns out at low magnetic field. Numerical simulations indicate a reduction of this worsening by a protrusion of the superconducting cup above the ferromagnetic one.
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3):8201305. DOI:10.1109/TASC.2012.2234817 · 1.32 Impact Factor
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    ABSTRACT: We studied the magnetic shielding properties of a MgB2/Fe hybrid structure consisting of two coaxial cups subjected to a magnetic field applied parallel to their axis. This study was performed to analyze the magnetic shield properties of a system contemporary exploiting the opposite magnetic properties of superconducting/ferromagnetic materials. The MgB2 cup was grown by a microwave-assisted Mg-infiltration technique that allows obtaining samples with different shapes and easily scalable sizes, meeting the requirements of different shielding applications. Measurements of mitigation of the magnetic induction were performed in applied magnetic field up to 1.5 T and in different positions along the cup axis at temperature T = 20 K. A decrease of the shielding factor (SF) of the hybrid system with respect to the MgB2 cup alone turns out at low magnetic field. On the contrary, at higher magnetic field the superposition of the two cups increases the SF of the hybrid system up to 3 times over that one of the single MgB2 cup.
    Journal of Superconductivity and Novel Magnetism 05/2013; 26(5):1513-1516. DOI:10.1007/s10948-012-1883-8 · 0.93 Impact Factor
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    ABSTRACT: This paper proposes a hybrid experimental-numerical technique, based on the boundary element method, able to reconstruct the magnetic field distribution in the free space outside the unknown field sources, without requiring the onerous process of source identification. The approach is validated by comparison with experimental data considering a Helmholtz coil system, where the connections of the coils and the supply currents can be controlled to generate different spatial distributions of the magnetic field. The presence of materials with high magnetic permeability, also involving eddy currents, is considered as well. An analysis on the reachable accuracy and on the related parameters is developed, with the final aim of obtaining a satisfactory compromise between result accuracy and experimental burden. Finally, the field values reconstructed by the proposed experimental-numerical technique are compared with the measured ones, showing a good agreement.
    IEEE Transactions on Magnetics 03/2013; 49(3):1143-1148. DOI:10.1109/TMAG.2012.2217751 · 1.21 Impact Factor
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    ABSTRACT: The paper investigates the heating of tissues exposed to millimeter and sub-millimeter electromagnetic waves. The problem is faced by assuming a plane wave normally incident to the surface of a layered model of the human body and by solving analytically both the electromagnetic and thermal equations. The effect of a possible variability in the relevant parameters is put in evidence through a specific parametric analysis.
    Electromagnetics in Advanced Applications (ICEAA), 2013 International Conference on; 01/2013