Experimental Validation of a 3D Microwave Imaging Device for Brain Stroke Monitoring

In this work we present the experimental validation of a 3D microwave imaging device to brain observation. The device is conceived as a way to monitor stroke development, supporting physicians in the follow-up of patients in the aftermath of cerebrovascular accidents, and giving to them extra information for decision-making and application of therapies. The device acquires data through antennas placed around the patient head, in a low-complexity system that guarantees that available information is enough for reliable outcome. Experimental testing is performed on a 3-D human-like head phantom with promising results

Hybrid Simulation-Measurement Calibration Technique for Microwave Imaging Systems

This paper proposes an innovative technique to calibrate microwave imaging (MWI) systems combining available measured data with simulated synthetic ones. The introduced technique aims to compensate the variations of the antenna array due to unavoidable manufacturing tolerances and placement, in comparison to the nominal electromagnetic (EM) scenario. The scheme is tested virtually and experimentally for the MWI of the adult human head tissues. The virtual EM analysis uses a realistic 3-D CAD model working together with a full-wave software, based on the finite element method. Meanwhile, the real implementation employs a single-cavity anthropomorphic head phantom and a custom brick-shaped antenna array working at around 1 GHz

Hybrid Resolvent Kernel Calibration Technique for Microwave Imaging Systems

This work assesses a hybrid calibration technique that uses together measured and simulated data to compensate modeling errors such as fabrication tolerances and positioning inaccuracies. Here, as a proof-of-concept, it is considered a virtual microwave imaging experiment of a human brain stroke condition. The test involves a full-wave software based on the finite element method and 3-D highly realistic system models, including a set of 24 monopoles immersed in a solid brick-shaped matching medium and a single-cavity anthropomorphic head phantom. The studied case shows that under favorable assumptions, the calibration procedure improves the quality of the retrieved images compared to the non-calibrated-kernel approach

Moving Forward to Real-time Imaging-based Monitoring of Cerebrovascular Diseases Using a Microwave Device: Numerical and Experimental Validation

This paper introduces a numerical and experimental assessment of the microwave device capabilities to perform continuous real-time imaging-based monitoring of a brain stroke, exploiting a differential measuring scheme of the scattering matrices and the distorted Born approximation. The device works around 1 GHz and consists of a low-complexity 22-antenna-array composed of custom-made wearable elements. The imaging kernel is built using an average-head reference scenario computed off-line via accurate numerical models and an in-house finite element method electromagnetic solver. The validation follows the progression of emulated evolving hemorrhagic stroke condition, including tests with both an average single-tissue head model and a multi-tissue one in the numerical part and the average scenario in the experimental one. The results show the system's capacity to localize and track the shape changes of the stroke-affected area in all studied cases

Open-ended coaxial probe measurements of complex dielectric permittivity in diesel-contaminated soil during bioremediation

In the bioremediation field, geophysical techniques are commonly applied, at lab scale and field scale, to perform the characterization and the monitoring of contaminated soils. We propose a method for detecting the dielectric properties of contaminated soil during a process of bioremediation. An open-ended coaxial probe measured the complex dielectric permittivity (between 0.2 and 20 GHz) on a series of six soil microcosms contaminated by diesel oil (13.5% Voil /Vtot ). The microcosms had different moisture content (13%, 19%, and 24% Vw/Vtot ) and different salinity due to the addition of nutrients (22 and 15 g/L). The real and the imaginary component of the complex dielectric permittivity were evaluated at the initial stage of contamination and after 130 days. In almost all microcosms, the real component showed a significant decrease (up to 2 units) at all frequencies. The results revealed that the changes in the real part of the dielectric permittivity are related to the amount of degradation and loss in moisture content. The imaginary component, mainly linked to the electrical conductivity of the soil, shows a significant drop to almost 0 at low frequencies. This could be explained by a salt depletion during bioremediation. Despite a moderate accuracy reduction compared to measurements performed on liquid media, this technology can be successfully applied to granular materials such as soil. The open-ended coaxial probe is a promising instrument to check the dielectric properties of soil to characterize or monitor a bioremediation process

Comparison of Reconstruction Algorithms for Brain Stroke Microwave Imaging

The aim of this paper is to describe and compare the performances of three image reconstruction algorithms that can be used for brain stroke microwave imaging. The algorithms belong to the class of non-linear iterative algorithms and are capable of providing a quantitative map of the imaged scenario. The first algorithm is the Contrast Source Inversion (CSI) method, which uses the Finite Element Method (FEM) to discretize the domain of interest. The second one is the Subspace-Based Optimization Method (SOM) that has some properties in common with the CSI method, and it also uses FEM to discretize the domain. The last one is the Distorted Born Iterative Method with the inverse solver Two-step Iterative Shrinkage/Thresholding (DBIM-TwIST), which exploits the forward Finite Difference Time Domain (FDTD) solver. The reconstruction examples are created with 3-D synthetic data modelling realistic brain tissues with the presence of a blood region, representing the stroke area in the brain, whereas the inversion step is carried out using a 2-D model

Assessing a Microwave Imaging System for Brain Stroke Monitoring via High Fidelity Numerical Modelling

This work presents the outcomes of a numerical analysis based on a 3-D high fidelity model of a realistic microwave imaging system for the clinical follow-up of brain stroke. The analysis is meant as a preliminary step towards the full experimental characterization of the system, with the aim of assessing the achievable results and highlight possible critical points. The system consists of an array of twenty-four printed monopole antennas, placed conformal to the upper part of the head; each monopole is immersed into a semi-solid dielectric brick with custom permittivity, acting as coupling medium. The whole system, including the antennas and their feeding mechanism, has been numerically modeled via a custom full-wave software based on the finite element method. The numerical model generates reliable electromagnetic operators and accurate antenna scattering parameters, which provide the input data for the implemented imaging algorithm. In particular, the numerical analysis assesses the capability of the device of reliably monitoring the evolution of hemorrhages and ischemias, considering the progression from a healthy statet o an early-stage stroke

Reentry vehicles: evaluation of plasma effects on RF propagation

In the frame of communication technology relevant to the re-entry vehicles, the communication black-out occurring in the presence of plasma is one of the main challenging issues. The re-entry plasma is a complex physical system, where the ionization derives from a shock-wave and non-equilibrium phenomena. As discussed elsewhere, the time scales of plasma dynamics (including its evolution along mission trajectory) and radio wave propagation are well separated so that radio wave propagation is solved at an appropriate number of time "snapshots" in which plasma dynamics is held unchanged and considered as known. In this activity, a consistent effort has been devoted to model the electromagnetic problem. For the involved range of oprative frequencies and expected densities, the plasma can be considered as an inhomogeneous dielectric. The associated electromagnetic problem is solved in two steps, via use of the field equivalence principle. The vehicle-plasma system is substituted by equivalent (Love's) currents on its boundary, radiating in free space; the fields at the boundary are obtained by solving the propagation problem from the antenna, installed on the spacecraft, up to the plasma boundary, through the Eikonal approximation. Radiation is then obtained without further approximations. Unlike other well-known numerical methods (e.g. FEM), this technique is not intrinsecally limited by the electrical dimension of the vehicle-plasma system. This enables to analyze high frequency problems. Since the formation of the re-entry plasma critically depends on the re-entry vehicle shape and kinematics, the related model has been directly derived from the output data of the Computational Fluid Dynamics simulations. All the results of the above mentioned activities have been collected in a new software, the AIPT (Antenna In Plasma Tool, integrated into ADF-EMS Antenna Design Framework Electromagnetic Satellite) able to predict the electromagnetic propagation in the presence of plasma