Nunzia Fontana

Non-thermal effects of 2.45 GHz microwaves on spindle assembly, mitotic cells and viability of Chinese hamster V-79 cells

The production of mitotic spindle disturbances and activation of the apoptosis pathway in V79 Chinese hamster cells by continuous 2.45 GHz microwaves exposure were studied, in order to investigate possible non-thermal cell damage. We demonstrated that microwave (MW) exposure at the water resonance frequency was able to induce alteration of the mitotic apparatus and apoptosis as a function of the applied power densities (5 and 10mW/cm(2)), together with a moderate reduction in the rate of cell division. After an exposure time of 15 min the proportion of aberrant spindles and of apoptotic cells was significantly increased, while the mitotic index decreased as well, as compared to the untreated V79 cells. Additionally, in order to understand if the observed effects were due to RF exposure per se or to a thermal effect, V79 cells were also treated in thermostatic bath mimicking the same temperature increase recorded during microwave emission. The effect of temperature on the correct assembly of mitotic spindles was negligible up to 41°C, while apoptosis was induced only when the medium temperature achieved 40°C, thus exceeding the maximum value registered during MW exposure. We hypothesise that short-time MW exposures at the water resonance frequency cause, in V79 cells, reversible alterations of the mitotic spindle, this representing, in turn, a pro-apoptotic signal for the cell line.

Investigation of maximum local specific absorption rate in 7 T magnetic resonance with respect to load size by use of electromagnetic simulations

Local specific absorption rate (SAR) evaluation in ultra high field (UHF) magnetic resonance (MR) systems is a major concern. In fact, at UHF, radiofrequency (RF) field inhomogeneity generates hot-spots that could cause localized tissue heating. Unfortunately, local SAR measurements are not available in present MR systems; thus, electromagnetic simulations must be performed for RF fields and SAR analysis. In this study, we used three-dimensional full-wave numerical electromagnetic simulations to investigate the dependence of local SAR at 7.0 T with respect to subject size in two different scenarios: surface coil loaded by adult and child calves and quadrature volume coil loaded by adult and child heads. In the surface coil scenario, maximum local SAR decreased with decreasing load size, provided that the RF magnetic fields for the different load sizes were scaled to achieve the same slice average value. On the contrary, in the volume coil scenario, maximum local SAR was up to 15% higher in children than in adults.

VALIDATION OF NUMERICAL APPROACHES FOR ELECTROMAGNETIC CHARACTERIZATION OF MAGNETIC RESONANCE RADIOFREQUENCY COILS

Numerical methods based on solutions of Maxwells equations are usually adopted for the electromagnetic characterization of Magnetic Resonance (MR) Radiofrequency (RF) coils. In this context, many difierent numerical methods can be employed, including time domain methods, e.g., the Finite-Difierence Time-Domain (FDTD), and frequency domain methods, e.g., the Finite Element Methods (FEM) and the Method of Moments (MoM). We provide

SAR prediction in adults and children by combining measured B1+ maps and simulations at 7.0 Tesla

To predict local and global specific absorption rate (SAR) in individual subjects.

A numerical assesment of the effect of MRI surface coils on implanted pacemakers

Electromagnetic interaction between a radio frequency surface coil for magnetic resonance imaging (MRI) and a heterogeneous human model implanted with a pacemaker system has been studied in order to provide safety requirements and to estimate potential damaging of the device. Since the coil can be considered an electrically small structure, an equivalent model has been considered and validated in order to reduce calculation burden in time domain simulation by using a Finite Integration Technique (FIT).

On the influence of a glass slide on the SAR distribution in Petri dishes for in vitro exposure to 2.45 GHz EM fields

In order to investigate possible effects on cultured cells of Electromagnetic (EM) fields in the frequency range typical of mobile communications, a large variety of in vitro exposure systems have been designed and numerically characterized. Important requirements for in vitro experiments comprise a high homogeneity of the Specific Absorption Rate (SAR) distribution [1] and the possibility of performing experiments at SAR levels in the range of the actual safety standards of 2 W/kg [2] to achieve a low temperature rise in the cell monolayers. In this paper, a numerical dosimetric analysis has been carried out through CST Microwave Studio® 2009. The homogeneity of the SAR distribution and the coupling of EM fields within the liquid in the presence of a glass slide as support for living cells, has been investigated as a function of the incident field polarization.

Multi-objective optimization of wideband spiral arrays

A challenging task in array design is to synthesize an array working at multiple frequencies within a large frequency band, with constraints imposed to the radiation pattern in terms of side lobe level (SLL). This kind of array synthesis requires a multi-objective approach since there is no single solution which can be considered the best at the multiple investigated frequencies for all the compulsory requirements. Therefore this class of problems, instead of a single one, is characterized by an ideal set of solutions, the Pareto front (PF), which comprises solutions over which no other solution of the population dominates [1]. This set provides a range of solutions for which no one can simultaneously satisfy the required performance but represents a tradeoff of the design requirements. Multi-objective genetic algorithms (MOAs) can be a useful tool for determining the Pareto front. They perform similarly to conventional genetic algorithms but they search for the set of solution which belongs to the PF, rather than providing only a single optimal solution. In particular, we have adopted a multi-objective genetic algorithm, called Non-dominated Sorting Genetic Algorithm (NSGA-II) [2] to optimize the array factor of a Spiral Array.

RF coil design for low and high field MRI: Numerical methods and measurements

Several clinical magnetic resonance applications at 1.5 T and higher field strengths require a careful selection of the RadioFrequency (RF) coil design to optimize the RF spatial distribution and sensitivity. Specifically, two basic requirements must be fulfilled for obtaining high quality images: in the transmission mode, RF coils must be able to produce a uniform magnetic field in the volume of interest so that the nuclei can be properly excited; in the receiving mode, a high signal to noise ratio is needed, and the coil must be able to collect the signal emitted by the nuclei with better sensitivity throughout the volume of interest. A number of analytical and numerical methods are reported in the literature to simulate the RF field distributions of surface and volume coils. In this work, we compared the performances of two computational methods (Method of Moments and Finite Elements Method), considering the modelling of both surface (single loop, figure of eight coil - FO8, dual loop) and volume (TEM) coils. Low (1.5 T) and high (7 T) field operating regimes have been analysed. Measurements obtained on the workbench and with a 1.5 T scanner are used for validation.

A novel coil for highly focused magnetic hyperthermia with nanoparticles

In this paper, we propose a novel coil for highly focused magnetic hyperthermia with nanoparticles, suitable for superficial treatments. The design has been carried out by using a commercial electromagnetic simulation software based on the Method of Moments (MoM).

Distributed trap FSS filter for dual tuned RF MRI coil decoupling at 7.0T

A new strategy for decoupling dual tuned coil by using a distributed Frequency Selective Surfaces based trap circuit is proposed. An example of a dual tuned coplanar and concentric coils tuned at the resonance frequencies of the hydrogenous (1H) and of the sodium (23Na) is shown.