1,721,148 research outputs found
Microwave ablation monitoring via microwave tomography: A numerical feasibility assessment
No full textMicrowave ablation is a cancer treatment based on the induction of coagulative necrosis of tumor cells by local heating. Recently, such a technique has progressed significantly in the clinical practice. However, its effectiveness would improve dramatically if paired with a system for the real-time monitoring of the evolving dimension and shape of the thermally ablated area. This paper explores the possibility of using microwave imaging as a convenient, non-invasive methodology to track the variation of the electromagnetic properties of ablated tissues and the surrounding region, so to monitor the overall treatment evolution in a non-invasive way. © 2016 European Association of Antennas and Propagation
Assessment of risk from exposure to electromagnetic fields emitted by hand-held jammers to defeat drone attacks
Full text linkIl Jammer è un dispositivo elettromagnetico in grado di interrompere il canale di radiocomunicazione e bloccare il segnale di comando di apparecchiature elettriche ed elettroniche, attraverso l'emissione di una serie di impulsi di campo elettromagnetico a radiofrequenza (RF) alle stesse frequenze del segnale da ostacolare. Il jammer rappresenta quindi una valida contromisura elettronica per la protezione da attacchi terroristici o dallo spionaggio, realizzati anche tramite droni. Tuttavia, poiché i jammer emettono intenzionalmente campi elettromagnetici a RF allo scopo di interferire deliberatamente con le comunicazioni radio, essi possono causare malfunzionamenti o guasti anche di apparecchiature elettriche amiche (ad. es. ricetrasmittenti, computer, ecc.) che si trovino all'interno del loro raggio di azione. Inoltre, le emissioni a RF dei jammer possono porre problemi anche riguardo al possibile superamento dei limiti di esposizione a campi elettromagnetici vigenti per la protezione da possibili rischi per la salute delle persone. Pertanto, nella maggior parte dei Paesi l'immissione sul mercato e l'utilizzo dei jammer è regolato da disposizioni rigorose ed è normalmente vietato senza una specifica autorizzazione governativa. Nel presente Rapporto tecnico si illustra il quadro normativo di riferimento inerente all'immissione sul mercato e all'uso dei jammer, ai requisiti di immunità irradiata relativi alla sicurezza di base e alle prestazioni essenziali delle apparecchiature elettriche, nonché ai limiti vigenti per l'esposizione umana a campi elettromagnetici ai fini della protezione da possibili rischi per la salute e la sicurezza. Inoltre, viene illustrato un caso di studio inerente ai campi elettromagnetici emessi da un jammer portatile per il contrasto degli attacchi con droni, con lo scopo di determinare le distanze di sicurezza per il rispetto dei requisiti di immunità irradiata delle apparecchiature elettriche e dei limiti per l’esposizione della popolazione.The Jammer is an electromagnetic device capable of interrupting the radio communication channel and blocking the command signal of electrical and electronic equipment, through the emission of a series of radio frequency (RF) electromagnetic field pulses at the same frequencies of the signal to be hindered. Therefore, the jammer can represent a valid electronic countermeasure for protection against terrorist attacks or espionage, carried out also by drones. Nevertheless, since jammers intentionally emit RF electromagnetic fields to deliberately interfere with radio communications, they may also cause malfunctions or failures of friendly electrical equipment (e.g., two-way radios, computers, etc.) within their action range. Furthermore, the RF emissions of jammers can pose problems regarding the possible exceeding of the restrictions on human exposure to electromagnetic fields for the protection from possible health risks. Hence, in most countries the placing on the market and the use of jammers is regulated by strict provisions and is normally prohibited without a specific government authorization. This Technical Report illustrates the regulatory framework concerning the placing on the market and use of jammers, the radiated immunity requirements relating to basic safety and essential performance of electrical equipment, as well as the restrictions on human exposure to electromagnetic fields for the purpose of protection against possible health and safety risks. In addition, a case study concerning electromagnetic fields emitted by a portable jammer for defeating drone attacks is illustrated, with the purpose to determine the relevant safety distances for compliance with the requirements for radiated immunity of electrical equipment and the exposure restrictions for the general public
A full-wave numerical assessment of microwave tomography for monitoring cancer ablation
No full textIn this communication, we present a full-wave numerical study aimed at showing the potential of microwave tomography as a tool to monitor microwave ablation of solid tumors. The goal is to track the changes in dielectric properties of the tissue undergoing the treatment, in order to appraise the evolving dimension and shape of the thermally ablated area surrounding the applicator. Such an in-line monitoring capability would entail a significant improvement in the therapeutic effectiveness of cancer treatments exploiting microwave ablation, both in terms of optimization/personalization of the therapeutic protocol and of reduction of unwanted side effects due to the unwanted increase of temperature in healthy tissues. The numerical study involves a scenario inspired by an existing experimental set-up, already used for the ex-vivo assessment of microwave ablation treatments. Hence, the promising results we have obtained, fully motivate us to progress towards the experimental demonstration of the concept in ex-vivo conditions. © 2017 Euraap
Ex vivo tissue shrinking in microwave thermal ablation
No full textAim of this study was to characterize the changes occurring in tissues undergoing microwave ablation, in order to more accurately predict the actual treated volume. Different experiments were conducted in restricted samples (10-40 mm side cubes) and in large samples of ex-vivo bovine liver, varying the deposited energy (60 W at 2.45 GHz, applied for 1-10 min). A comparison between pre- and post-ablation dimensions was conducted, pointing out a substantial shrinkage, non-uniform over time and space, asymmetrical along the microwave antenna axis and perpendicularly to it. The obtained results show a complex tissue behavior and a correlation between the carbonized area and the contraction phenomenon. © 2015 EurAAP
Exploiting Microwave Imaging Methods for Real-Time Monitoring of Thermal Ablation
No full textMicrowave thermal ablation is a cancer treatment that exploits local heating caused by a microwave electromagnetic field to induce coagulative necrosis of tumor cells. Recently, such a technique has significantly progressed in the clinical practice. However, its effectiveness would dramatically improve if paired with a noninvasive system for the real-time monitoring of the evolving dimension and shape of the thermally ablated area. In this respect, microwave imaging can be a potential candidate to monitor the overall treatment evolution in a noninvasive way, as it takes direct advantage from the dependence of the electromagnetic properties of biological tissues from temperature. This paper explores such a possibility by presenting a proof of concept validation based on accurate simulated imaging experiments, run with respect to a scenario that mimics an ex vivo experimental setup. In particular, two model-based inversion algorithms are exploited to tackle the imaging task. These methods provide independent results in real-time and their integration improves the quality of the overall tracking of the variations occurring in the target and surrounding regions. © 2017 Rosa Scapaticci et al
The use of CT to improve the knowledge of the physical phenomena associated with microwave thermal ablation procedures
No full textThis study aims at developing and optimizing a set-up suitable for real-time investigations on the structural and dynamical changes occurring in a biological tissue during a microwave ablation treatment. © 2015 IEEE
Experimental characterisation of the thermal lesion induced by microwave ablation
No full textPurpose: This work focuses on the characterisation of the ablated area induced by a microwave thermal ablation (MTA) procedure. An experimental methodology for establishing a straightforward correlation between the temperature gradient and the changes in the dielectric properties of the tissue is presented and discussed. Materials and methods: Temperature measurements were performed during an ablation procedure in ex vivo bovine liver, at different distances from the antenna, whereas measurements of complex permittivity were conducted in sagittal sections of the ablated samples. The measured temperatures and dielectric properties were then correlated to obtain the dependence of the dielectric properties' spatial variation on the temperature gradient. The obtained correlation has been validated through comparison with previously obtained experimental data. A weighted cubic polynomial function and a weighted sigmoid function have been tested for best-fit interpolation of the measured data. Results: Temperatures in the range 23-105 °C were measured during the MTA procedure, while, after the end of the MTA trials, relative permittivities in the range 7-43 and electric conductivities in the range 0.3-1.8 S/m were measured according to the distance from the antenna's axis. The polynomial function showed better regression coefficients than the sigmoid one for both the relative permittivity (R2= 0.9947 versus R2= 0.9912, respectively) and the conductivity (R2= 0.9919 versus R2= 0.9866, respectively). However, the weighted cubic function showed an unrealistic behaviour for the relative permittivity at temperatures lower than 40 °C. Conclusions: According to the results obtained, information on the changes in the dielectric properties of the tissue under MTA treatment could be inferred from measured temperature data. Once validated by in vivo studies, the proposed methodology could be exploited to develop predictive tools for treatment planning. © 2014 Informa UK Ltd
Quality factor for the measurement of dielectric properties of biological tissues
No full textThe knowledge of dielectric properties of biological tissue is of fundamental importance for the development of diagnostic or therapeutic applications of electromagnetic fields, as microwave imaging or microwave thermal ablation. In this paper, a quality factor is introduced to identify the soundness of measurements of dielectric properties performed with different set-ups and procedures. © Institution of Engineering and Technology.All Rights Reserved
Microwave thermal ablation: Performed studies and research needs
No full textMicrowave thermal ablation (MTA) procedures are based on the absorption of an electromagnetic field irradiated by a minimally invasive antenna. Several studies have been conducted in the past considering different aspects of the technique. However, some points still need to be investigated, as pointed out in the present contribution. © 2017 IEEE
CT-based investigation of the contraction of ex vivo tissue undergoing microwave thermal ablation
No full textTreatment planning in microwave thermal ablation (MTA) requires the capability to predict and estimate the shape and dimension of the thermally coagulated zone obtainable following a clinical protocol. The ultimate result relies on the knowledge of the performance of the ablation device, as well as of the temperature-dependent structural modifications that the tissue undergoes during the treatment, because of the very high temperatures reached (up to 100 °C or higher). In this respect, tissue shrinkage plays an important role, since the dimension of the ablated tissue evaluated at the end of the MTA procedure (e.g. by way of CT imaging) could underestimate the actual treated tissue, leading to inaccurate assessment of the treatment outcome. In this study, CT imaging was used for real-time monitoring of tissue contraction during MTA experiments carried out in ex vivo bovine liver. Fiducial lead markers were positioned into the tissue in a 3D spatial grid around the MTA applicator. The spatial and temporal evolution of tissue contraction was imaged during the experiments, and analysed in terms of displacements of clusters of fiducial markers. The results obtained indicated that contraction is highly heterogeneous in the zone of ablation, depending both on the heating and on interactions with nearby tissue. In particular, tissue shrinkage appeared asymmetric with respect to the direction of insertion of the microwave applicator in the central area of carbonised tissue (about 30% and 19% along the radial and longitudinal directions, respectively), and isotropic in the region of coagulated (but not carbonised) tissue (about 11%). The total ablated volume was reduced by approximately 43% with respect to its pre-ablation value. Finally, temperature measurements displayed a correlation between temperature increment and temporal evolution of tissue contraction in the zone of ablation. © 2018 Institute of Physics and Engineering in Medicine
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