1,720,977 research outputs found
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 straight-forward 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 degrees 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 (R-2 0.9947 versus R-2 0.9912, respectively) and the conductivity (R-2 0.9919 versus R-2 0.9866, respectively). However, the weighted cubic function showed an unrealistic behaviour for the relative permittivity at temperatures lower than 40 degrees 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.Purpose: 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 (R21⁄40.9947 versus R21⁄40.9912, respectively) and the
conductivity (R21⁄40.9919 versus R21⁄40.9866, 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
Changes in the dielectric properties of ex vivo bovine liver during microwave thermal ablation at 2.45 GHz
No full textIn microwave thermal ablation (MTA) therapy, the dielectric properties of the target tissue play an important role in determining the radiation properties of the microwave ablation antenna. In this work, the ex vivo dielectric properties of bovine liver were experimentally characterized as a function of the temperature during MTA at the frequency of 2.45 GHz. The obtained data were compared with measurements performed at the end of the MTA treatment, and considering the heating achieved with a temperature-controlled water bath. Finally, measured data were used to perform a numerical study evaluating the effects of changes in tissue's dielectric properties during the MTA treatment on the radiation properties of a microwave interstitial ablation antenna, as well as on the obtained thermal lesion. Results evidenced a significant decrease of both relative permittivity (about 38%) and electric conductivity (about 33%) in the tissue during treatment as the temperature increased to over 60 °C, with a dramatic drop when the temperature approached 100 °C. Moreover, the numerical study evidenced that changes in tissue's dielectric properties during the MTA treatment affect the distribution of the power absorbed by the tissue (specific absorption rateSAR, W kg 1) surrounding the microwave interstitial ablation antenna, leading to a peak SAR up to 20% lower, as well as to a thermal lesion up to 8% longer. This work may represent a preliminary step towards the future development of a procedure for MTA treatment planning. © 2012 Institute of Physics and Engineering in Medicine
An ex vivo study on the shrinkage occurring in bovine liver during microwave thermal ablation: carbonized vs coagulated tissue
No full textThis work aims at deepening the comprehension of this phenomenon, proposing two novel set ups for the characterization of the tissue contraction in correlation with the physical status of the ablated tissue, i.e. to its temperature
Early life exposure to 2.45GHz WiFi-like signals: Effects on development and maturation of the immune system
No full textThe development of the immune system begins during embryogenesis, continues throughout fetal life, and completes its maturation during infancy. Exposure to immune-toxic compounds at levels producing limited/transient effects in adults, results in long-lasting or permanent immune deficits when it occurs during perinatal life. Potentially harmful radiofrequency (RF) exposure has been investigated mainly in adult animals or with cells from adult subjects, with most of the studies showing no effects. Is the developing immune system more susceptible to the effects of RF exposure? To address this question, newborn mice were exposed to WiFi signals at constant specific absorption rates (SAR) of 0.08 or 4 W/kg, 2h/day, 5 days/week, for 5 consecutive weeks, starting the day after birth. The experiments were performed with a blind procedure using sham-exposed groups as controls. No differences in body weight and development among the groups were found in mice of both sexes. For the immunological analyses, results on female and male newborn mice exposed during early post-natal life did not show any effects on all the investigated parameters with one exception: a reduced IFN-γ production in spleen cells from microwaves (MW)-exposed (SAR 4 W/kg) male (not in female) mice compared with sham-exposed mice. Altogether our findings do not support the hypothesis that early post-natal life exposure to WiFi signals induces detrimental effects on the developing immune system
A Wire Patch Cell Exposure System for in vitro Experiments at Wi-Fi Frequencies
No full textIn order to study possible biological effects of electromagnetic (EM) fields generated by Wi-Fi devices, an exposure system based on a Wire Patch Cell (WPC) has been designed, fabricated and fully characterized. The system is suitable to expose, in the whole band of the Wi-Fi signal, cell monolayers plated on the bottom of four 35-mm Petri dishes, filled with 2 or 3 mL of biological medium. Results of numerical and experimental characterization indicate quite good efficiency values, with acceptable homogeneity of the dose. Being an open system, the WPC needs a shielding arrangement when placed inside the incubator during the experiments. It has been proven that this arrangement effectively shields the incubator and does not modify the scattering parameter S(11) of the structure
Valutazione dell’esposizione ai campi elettromagnetici generati dalle nuove tecnologie Wireless Power Transfer
Full text linkIl trasferimento di potenza senza contatto, o wireless power transfer (WPT), consiste nella trasmissione di energia elettrica da un dispositivo primario trasmittente (TX), collegato alla fonte di alimentazione, a un dispositivo secondario ricevente (RX), collegato al carico elettrico, senza l'uso di connettori fisici bensì mediante accoppiamento elettromagnetico. Nikola Tesla, all’inizio del XX secolo, dedicò molti sforzi alla progettazione e realizzazione di sistemi elettrici in grado di trasportare l’energia in modalità wireless. Tuttavia, a causa della limitata efficienza di trasferimento nonché dei campi elettrici elevatati, tale tecnologia è rimasta di fatto poco più di una curiosità ingegneristica fino a circa 30 anni fa, allorché è iniziata la diffusione massiva di dispositivi elettronici personali (ad es. laptop, tablets, telefoni cellulari, ecc.) per i quali la tecnologia WPT rappresenta un’opzione interessante soprattutto in relazione alla flessibilità di utilizzo. Più recentemente, lo sviluppo della tecnologia WPT basata sull’accoppiamento magnetico risonante ha consentito un significativo incremento dell’efficienza di trasferimento della potenza in tempi abbastanza rapidi, aprendo così la strada alla penetrazione della tecnologia WPT nel mercato dei veicoli elettrici per il quale si prevede una forte espansione nei prossimi anni. Ciò pone una serie di sfide, sia dal punto di vista tecnologico, vista l’esigenza di realizzare sistemi WPT in grado di trasferire potenze anche elevate in maniera efficiente e in tempi contenuti, sia dal punto di vista protezionistico, poiché si pone la necessità di limitare l’esposizione umana ai campi elettromagnetici (CEM) che vengono generati durante il trasferimento di potenza wireless affinché siano rispettati i limiti di legge. Con riferimento a quest’ultimo aspetto, si pone quindi la necessità di definire procedure standardizzate per la valutazione dell’esposizione umana ai CEM generati dai sistemi WPT ai fini della verifica di conformità ai pertinenti limiti normativi: a questo stanno attualmente lavorando i comitati elettrotecnici normatori preposti, sia in ambito nazionale (Comitato Elettrotecnico Italiano, CEI-CT106) che internazionale (International Electrotechnical Commission, IEC-TC106). Il presente articolo vuole fornire una descrizione della tecnologia WPT e delle sue principali applicazioni, nonché delle metodologie standardizzate per la valutazione dell’esposizione ai campi elettromagnetici generati dai sistemi WPT secondo i requisiti della normativa tecnica
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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