1,720,985 research outputs found
Moving Forward to Real-time Imaging-based Monitoring of Cerebrovascular Diseases Using a Microwave Device: Numerical and Experimental Validation
Get PDFThis 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
Hybrid Simulation-Measurement Calibration Technique for Microwave Imaging Systems
Get PDFThis 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
Broadband Microwave Antenna for Imaging and Sensing in Biomedical Applications
Get PDFThanks to their operation band, broadband an-tennas demonstrate applicability and versatility in biomedical sensing and imaging. This work presents the numerical validation of a microwave broadband monopole antenna aimed for work in close proximity to biological tissues, such as the human head. An iterative design starting from an elliptical patch antenna reduces geometry dimensions and enhances bandwidth efficiency. The final design achieves a compact 48×38mm antenna with a dielectrically custom-made 3 mm-thickness matching layer covering a -10 dB frequency band from 1 to 6GHz, which is assessed on top of a simplified multilayer head phantom
Assessing a Microwave Imaging System for Brain Stroke Monitoring via High Fidelity Numerical Modelling
Get PDFThis 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
Microwave antenna array calibration via simulated and measured S-parameters matching
Get PDFThis paper extends the validation of an innovative calibration framework for microwave imaging systems combining measured scattering parameters with numerically simulated ones. The aim is to improve the imaging operator accuracy by overcoming possible variations between the measurement system and its numerical model. Here, we investigate the possibility of reconstructing the transmission coefficients, measured at the antenna ports, employing a custom set of simulations where manufacturing tolerances are introduced. The experimental validation considers a microwave antenna array designed for brain imaging; each antenna is immersed in a brick of custom coupling medium whose dielectric properties variability is mainly analyzed. Further, the simulated dataset is provided by a high-fidelity full-wave electromagnetic tool, based on the finite element method, and coupled with a 3-D CAD model. This work presents an essential step forward in the whole calibration scheme, to then be able to estimate the electric field within the domain of interest, thus improve the imaging operator
Compact Wearable Broadband Antenna for Head Microwave Sensing and Imaging
Get PDFMicrowave sensing and imaging technologies are gaining interest and reliability in diagnosing and monitoring pathologies in which there is a change in the dielectric properties of tissues, such as stroke, Alzheimer’s, and brain tumors in the head. For this reason, there is a need for broadband sensors/antennas working in microwave frequencies to make non-invasive devices able to detect and monitor these pathologies. In this work, we present a flexible and compact antenna optimized for microwave head imaging and sensing, operating in a frequency range of 1.3 GHz−4.7 GHz. It consists of a printed z-shaped monopole with a frontal block of flexible material with custom permittivity and conductivity that improves field penetration into the tissues and reduces the mismatch between the head and the surrounding media
Nonlinear Correction of the Direct Inverse Problem Solution in Real-Time Imaging
Get PDFThis paper proposes a direct method for quantitative real-time imaging based on a nonlinear correction of the approximate linearized imaging kernel. The correction process relies on a pseudo-Rytov approximation employing the ratio between the total and incident fields in the scattering model, which can be estimated analytically. Unlike traditional iterative algorithms, there is no need for multiple computations of the direct scattering model, gaining computational speed and robustness to numerical inaccuracies. The procedure consists of two steps. First, a fast direct inversion algorithm based on the Born approximation provides the initial guess for the permittivity distribution; this study employs the Truncated Singular Value Decomposition (TSVD) and an in-house finite element-based solver to compute the imaging operator. Second, the field correction factor is transferred onto the object's permittivity to enhance its quantitative accuracy. The proposal viability is verified in 2D synthetic experiments at microwave frequencies, verifying improvements in the reconstructed unknown permittivity
Low Computational Demand Nonlinear Correction of the Inverse Problem in Microwave Brain Imaging
Get PDFThis paper investigates a nonlinear correction factor for the direct inverse problem solution in medical microwave imaging (MMI), focusing on acute brain stroke monitoring. The correction factor relies on a pseudo-Rytov approximation, which
employs the ratio between total and incident electric fields in the scattering model to enhance quantitative accuracy. This approach enables the direct correction of the approximate linearized imaging kernel without requiring iterative computations
of the direct scattering model, significantly reducing the inversion computational effort and improving the system’s robustness to numerical inaccuracies. MMI represents a promising modality for fast, potentially real-time response, delivering quantitative
insights that complement gold-standard imaging techniques. This study presents a realistic numerical experiment for hemorrhagic stroke detection, demonstrating the proposed correction’s impact on the accuracy of dielectric contrast reconstruction within a 3-D imaging framework and underscoring its potential benefits for
clinical applications
Wearable Microwave Imaging System for Brain Stroke Imaging
Get PDFThis paper presents the experimental validation of the detection capabilities of a low complexity wearable system designed for the imaging-based detection of brain stroke. The system approaches the electromagnetic inverse problem via a 3-D imaging algorithm based on the Born approximation and the Truncated Singular Value Decomposition (TSVD). For testing, flexible antennas with custom-made coupling-medium are prototyped and assessed in mimicked hemorrhagic and ischemic stroke conditions. The experiment emulates the clinical scenario using a single-tissue anthropomorphic head phantom and strokes with both 20 cm 3 and 60 cm 3 ellipsoid targets. The imaging kernel is computed via full-wave simulation of a virtual twin model. The results demonstrate the capabilities for detecting and estimating the stroke-affected area
Hybrid Resolvent Kernel Calibration Technique for Microwave Imaging Systems
Get PDFThis 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
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