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Contamination with foreign objects is one of the main causes of customers? complaints against food manufacturers. Although different technologies are used for food and beverage inline monitoring, cases of contaminated food products still reach the market, many of which involve plastic and glass fragments. In this article, we propose the use of a microwave imaging (MWI) technology to monitor packaged foods along production lines. In this framework, MWI exploits the differences in dielectric properties between the food and the contaminant as well as the differences between faulty and unaltered items. A dedicated MWI system is designed and validated through numerical simulations. Then the prototype device is assessed experimentally, both in controlled laboratory conditions and on an industrial production line. The results of this study show the capabilities of this technology for food safety and security.

In this article, a method is presented to estimate the effective electrical parameters of the scatterers for multi-view multi-static two dimensional transverse electric (2D-TE) scattering configurations. The derived method needs the shape and position information of scatterers a-priorly to model the targets as circular cylinders (i.e., an effective radius and center is determined for each target) with constant electrical parameters. Next, the method employs the virtual experiments to focus the incident magnetic field as a $J_{0}$ on a specific target. After focusing the excitation and neglecting the multiple scattering between targets, the scattered field is in $H_{1}^{(1)}$ form. Next, the error between the simulated and the virtual fields is calculated. Then, the effective electrical parameter is estimated as the minimizer of the error. Lastly, for the cases where the shape and/or position information are noisy, the introduced method links the deviation of the electrical parameters to deviations of the effective radius and center. From this relation, the method presents a way to estimate the maximum deviations in the electrical parameters, given the maximum deviations in effective radius and center. The efficiency and accuracy of the proposed formulations are tested with both numerical and experimental examples.

Microwave imaging (MWI) for biomedical applications has drawn great attention in recent decades owing to its attractive features such as low cost, portability, and use of non-ionizing radiation. In the microwave imaging system, the antenna plays the most crucial role because it dictates the amount of electromagnetic power transmitted to the human body. In this contribution, an ultra-wideband antipodal Vivaldi antenna was designed for a biomedical MWI system. The antenna is immersed in a coupling medium of permittivity 23 and operates in the frequency band 0.5 – 5 GHz. The radiation of the antenna was improved by removing a piece of substrate from the aperture and replacing it with a high permittivity ceramic cone lens. Such a ceramic lens was capable to increase antenna radiation without changing the antenna impedance. This study paves the way for the assessment of a biomedical microwave imaging system.

Magnetic nanoparticles enhanced microwave imaging relies on the capability of modulating the response of such nanocomponents at microwaves by means of a (low frequency) polarizing magnetic field. In medical imaging, this capability allows for the detection and imaging of tumors loaded with nanoparticles. As the useful signal is the one which arises from nanoparticles, it is crucial to remove sources of undesired disturbance to enable the diagnosis of early-stage tumors. In particular, spurious signals arise from instrumental drift, as well as from the unavoidable interaction between the polarizing field and the imaging system. In this paper, we experimentally assess and characterize such spurious effects in order to set the optimal working conditions for magnetic nanoparticles enhanced microwave imaging of cancer. To this end, simple test devices, which include all components typically comprised in a microwave imaging system, have been realized and exploited. The experiment’s results allow us to derive design formulas and guidelines useful for limiting the impact of unwanted magnetic effects, as well as that relative to the instrumental drift on the signal generated by the magnetic nanoparticles-loaded tumor.

In this paper, an innovative approach to microwave imaging that combines qualitative imaging and deep learning is presented. The goal is to set a framework for a reliable and user-independent retrieval of the shapes of unknown targets. To this end, the proposed approach exploits an inversion technique known as orthogonality sampling method, which is capable of providing a qualitative estimation of the shape of targets in real-time. The output of the qualitative inversion is processed by a deep learning fully convolutional network called U-Net. U-Net automatically generates binary masks depicting the geometrical properties of the targets, i.e., separates the scattering objects (foreground) from the background. A quantitative assessment of the performance of the processing framework is provided with simulated data to demonstrate the capabilities of the proposed approach.

The incidence rate of breast cancer among women worldwide shows an increasing trend. Early detection plays a key role in increasing women's chances of survival. Several breast-imaging methods are currently used. However, due to the limitations of each of them, the proposal of new methods for breast imaging is still a hot topic in the scientific community. Among the proposed solutions, microwave imaging systems are attracting great interest, thanks to the significant dielectric contrast between healthy and tumor tissues of the breast. Several prototypes with central frequencies from few to tens of GHz have been proposed, both based on radar and tomographic reconstructions. In this paper, a quantitative solution combining both approaches for millimeter wave imaging of the breast is proposed. In particular, the radar approach is used to quickly detect the possible presence of a suspicious region, while the derivation of the nature of the lesion is pursued via a tomographic approach. Here the main idea is presented, along with a possible road map for further developments.

Quality control is of great importance in food industry, both for the evaluation of product characteristics and to avoid the occurrence of foreign bodies contamination in packaged items. With respect to the inspections against possible contaminants inside the product, different technologies are currently adopted along production chain lines. However, the number of accidents involving low density objects remains very large. To overcome this limitation, the use of electromagnetic technologies has been recently proposed. In this work, the synergic use of terahertz and microwaves technologies is proposed, so to provide high resolution images and in-depth inspections of different scenarios, including low density materials. A focus study on sugar samples is considered, reporting both its broadband characterization at microwaves and preliminary terahertz imaging to evaluate the integrity of the packaging. Ongoing research is devoted to the development and validation of a microwave device for monitoring food products along the production line.

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 state to an early-stage stroke.

The dielectric properties of bones are found to be influenced by the demineralisation of bones. Therefore, microwave imaging (MWI) can be used to monitor in vivo dielectric properties of human bones and hence aid in the monitoring of osteoporosis. This paper presents the feasibility analysis of the MWI device for monitoring osteoporosis. Firstly, the dielectric properties of tissues present in the human heel are analysed. Secondly, a transmission line (TL) formalism approach is adopted to examine the feasible frequency band and the matching medium for MWI of trabecular bone. Finally, simplified numerical modelling of the human heel was set to monitor the penetration of E-field, the received signal strength, and the power loss in a numerical model of the human heel. Based on the TL formalism approach, 0.6–1.9-GHz frequency band is found to feasible for bone imaging purpose. The relative permittivity of the matching medium can be chosen between 15 and 40. The average percentage difference between the received signal for feasible and inconvenient frequency band was found to be 82%. The findings based on the dielectric contrast of tissues in the heel, the feasible frequency band, and the finite difference time domain simulations support the development of an MWI prototype for monitoring osteoporosis. The research leading to these results has received funding from the European Research Council under the European Union’s Horizon 2020 Programme/ERC Grant Agreement BioElecPro no. 637780 and from the EMERALD project funded from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 764479. This work is also supported by COST Action MyWAVE CA17115 with an STSM grant entitled “European network for advancing Electromagnetic hyperthermic medical technologies.” peer-reviewed 2022-03-30

Thermal ablation treatment of cancer is increasingly adopted in the clinical practice, being minimally invasive and highly specific. However, a significant drawback of the technique is the lack of effective imaging modalities for monitoring the changes undergoing in the thermally treated tissue. In this respect, microwave imaging has been proposed as a possible candidate, owing to its portability, low-cost, non-ionizing nature, and capability to detect changes in dielectric properties of tissues induced by the temperature. The goal of this paper is to provide initial guidelines for the design of a microwave imaging system for thermal ablation monitoring. To this end, an analytical study is performed to determine the proper working conditions, in terms of frequency band and matching medium. Then, three antipodal Vivaldi antennas on different dielectric substrates are designed and numerically assessed. Among those antennas, the Vivaldi antenna on RT/duroid 6010LM substrate proved to be the most suitable choice. The results of this study pave the way to an experimental assessment of the potential of microwave imaging as a modality to monitor thermal ablation treatments.

This paper presents a study on the convergence criteria of amethod of moment based software. A mesh convergence study on a simple dipole antenna and a more complex antipodalVivaldi antenna was performed through WIPL-D environment. The Vivaldi antenna can be used for microwave imaging ofliver thermal ablation treatments.

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.

In this paper, we introduce a novel microwave imaging method using spherical harmonics and the sparse processing. As the sources of the spherical harmonics, we use the multipoles of different order. Based on theoretical considerations and as shown by numerical examples this approach is capable of retrieving concave shapes, which is particularly interesting when imaging complex-shaped targets. In this paper, we limit ourselves to the utilization of the multipoles parallel to the z-axis. We implement rigorous analytical expressions describing the first three multipole orders to improve the method's accuracy. As a test bed we analyze a centered and an offset star-shaped object in the presence of noise. For such a meaningful case, satisfying results have been obtained.

Due to the plethora of possible applicative fallouts, in the recent years several efforts have been made to develop three-dimensional (3-D) field intensity shaping methods. While many approaches able to focus a wave-field into a target point are available, few strategies have been instead developed to generate a field having a given intensity spatial distribution. This is probably due to the higher challenging nature of such a problem. In this letter, with reference to scalar fields, we present an innovative 3-D shaping procedure, which casts the problem as the solution of a finite number of convex programming problems. An example of the performance of the proposed procedure in a 3-D inhomogeneous scenario is given to show the capability of ensuring uniform field intensity within a target area while keeping it arbitrarily bounded elsewhere.

Magnetic nanoparticles-aided microwave imaging is an emerging modality for the diagnosis of early stage tumors. It exploits the possibility of modulating the response at microwaves of magnetic nanoparticles, employed as contrast agent selectively accumulated into the tumor. In this paper, we describe the results of an experimental study aimed at establishing the actual detection limits of the approach, namely the minimum amount of magnetic nanoparticles to be delivered for a reliable imaging. The assessment is carried out on breast phantoms made of ex-vivo minced pig tissues and using commercially available magnetic nanoparticles. The results show that it is possible to detect amounts of magnetic nanoparticles between 2 and 7 mg, dispersed in a volume of about one cubic centimeter, depending on the breast type. While such quantities are already consistent with those currently reachable via active selective targeting, an in-depth analysis of the results allows to identify strategies to further lower the detection limits up to four times, by refining the measurement set-up and setting the amplitude of the polarizing magnetic field modulating the nanoparticle response to a suitable value.

Breast cancer is one of the leading causes of cancer death among women in industrialized countries. Several microwave imaging systems have been proposed for the diagnosis of breast cancer, based on both the tomographic and radar approach, being tested in some cases even on real patients. However, the low working frequency of all these systems, which allows to reach non superficial targets, has been in some cases the main cause of a non-optimal resolution. Based both on the results of recent dielectric characterization campaigns on ex-vivo tissues of the human breast up to 50 GHz and on the promising achievements of the feasibility studies of mm-wave imaging systems, in this article, the tomographic approach to manipulate the simulated results of a linear radar scenario at the frequency of 30 GHz is proposed. In particular, two image reconstruction techniques, the Linear Sampling Method and the Born Approximation, are proposed and compared.

Foreign body contamination is a key issue in food production and packaging industries. The constant increase of mechanized process chain, the variety of materials employed during the production and the growing consumer awareness about food quality arose the number of complaints in the recent years. Several technologies are applied to ensure that products are free from contaminations, but they may fail in detecting low-density plastic or glass fragments contaminants accidentally present inside food/beverage products. To address this issue, a system exploiting microwave imaging is proposed and assessed in this work. To this end, we designed a system which is capable of monitoring of packaged food along the production line, taking into account the specific and challenging constraints arising in such a scenario. Its design and full characterization with full-wave simulation are reported in the paper. The obtained results set the ground for the realization of the prototype of the system.

The accidental foreign bodies contamination is still a major issue for food manufacturing industries. The continuous growth of automation along production lines together with the increasing attention of the customers towards food products quality, improved the industries care aiming to avoid complaints and ensure the best possible quality. As a matter of fact, several technologies are employed, but they lack in detecting certain class of contaminants, such as low-density plastics or small glass fragments that could turn into a severe threat, in particular for children. This work proposes a microwave imaging system in order to overcome these limitation in employed technologies. The design and characterization are reported in this paper; the simulations are addressed to the realization of a system prototype.

Chemotherapy treatment is a commonly used approach for treatment of localized malignant breast tumors. Ensuring accurate and reliable monitoring of the malignant tumor response to therapy can lead to the better follow-up care; thus, it would aid to increase the patient survival rate. In this paper, we introduce a microwave imaging system that can be used for breast cancer diagnostics and monitoring. The system is modeled in CST Microwave Studio and homogeneous breast model was used in order to assess its performance. Additionally, we propose a qualitative inverse scattering approach based on factorization method which allows us to monitor disease’s evolution during and after the treatment. Results reported present preliminary assessment of proposed imaging approach and serve as a guideline for future work considerations.

International audience; This work focuses on brain stroke imaging via microwave technology. In particular, the open issue of monitoring patients after stroke onset is addressed here in order to provide clinicians with a tool to control the effectiveness of administered therapies during the follow-up period. In this paper, a novel prototype is presented and characterized. The device is based on a low-complexity architecture which makes use of a minimum number of properly positioned and designed antennas placed on a helmet. It exploits a differential imaging approach and provides 3D images of the stroke. Preliminary experiments involving a 3D phantom filled with brain tissue-mimicking liquid confirm the potential of the technology in imaging a spherical target mimicking a stroke of a radius equal to 1.25 cm.

The orthogonality sampling method (OSM) is a recently introduced qualitative inverse scattering approach for the estimation of the morphological properties of unknown targets. Both the simplicity of implementation and the applicability to various measurement configurations make this method very effective. In this article, a general physical understanding of this otherwise & x201C;pure mathematical & x201D; method is given for the first time. Such an interpretation is derived from the relationship between the currents induced in the investigated scenario and the so-called reduced scattered field, which is the core of the orthogonality sampling indicator function. Interestingly, the nature of such a relationship implies that the reduced scattered field can be related to the radiating component of the induced currents. A direct consequence of such a result is that the OSM is capable of imaging discontinuities within the unknown targets and hence identify regions with different electromagnetic properties. This possibility represents a unique feature among qualitative inverse scattering methods, as these latter have been introduced as tools to image just the external shape of the unknown targets. The new interpretation as well as the above distinctive capability of the OSM are proved with examples on both simulated and experimental data.

In this letter, we describe and validate a microwave antenna designed for an imaging device for the diagnosis and monitoring of cerebrovascular pathologies. The antenna consists of a printed monopole immersed in a parallelepipedic block of semiflexible material with custom-permittivity, which allows to avoid the use of liquid coupling media and enables a simple array arrangement. The “brick” is built with a mixture of urethane rubber and graphite powder. The $-$ 10 dB frequency band of the antenna is 800 MHz—1.2 GHz, in agreement with the device requirements. The designed brick antenna is assessed in terms of power penetration, reflection, and transmission coefficients. To show the performance of the antenna in the relevant application scenario, an experiment has been carried out on an anthropomorphic head phantom, measuring the differential signals between healthy state and hemorrhagic stroke mimicking condition for different antennas positions.

Brain stroke is one of the most common diseases worldwide. Magnetic resonance imaging and computerized tomography are currently the two most assessed and reliable diagnostic tools, of great support to the clinicians. However, these devices are costly, time consuming and not portable, so that they are not appropriate for bedside monitoring. Hence, there is an increasing worldwide interest to develop complementary techniques to continuously monitor a patient after the stroke onset. In this paper, we report about the experimental testing of a novel device able to monitor cerebrovascular diseases, whose realization is based on microwave imaging technology. A 2-D version of the device has been fully experimentally tested and its 3-D version is under development.

This paper experimentally validates the capability of a microwave prototype device to localize hemorrhages and ischemias within the brain as well as proposes an innovative calibration technique based on the measured data. In the reported experiments, a 3-D human-like head phantom is considered, where the brain is represented either with a homogeneous liquid mimicking brain dielectric properties or with ex vivo calf brains. The microwave imaging (MWI) system works at 1 GHz, and it is realized with a low-complexity architecture formed by an array of twenty-four printed monopole antennas. Each antenna is embedded into the “brick” of a semi-flexible dielectric matching medium, and it is positioned conformal to the head upper part. The imaging algorithm exploits a differential approach and provides 3-D images of the brain region. It employs the singular value decomposition of the discretized scattering operator obtained via accurate numerical models. The MWI system analysis shows promising reconstruction results and extends the device validation.

Magnetic nanoparticles (MNP) enhanced microwave imaging could provide an effective approach for an early stage diagnosis of breast cancer, if encouraging results coming from accurate and realistic numerical studies are confirmed by an experimental proof of concept framework. To this end, an ad hoc laboratory setup has been designed and built up to verify the possibility of detecting the low signal scattered by MNP when embedded into a simplified but realistic breast phantom. This paper describes the developed measurement setup and the results coming from a first run of experiments, which confirm the possibility to detecting realistic amounts of accumulated nanoparticles. Moreover, the experimental results analysis allows addressing the future developments required to determine the ultimate detection limits of the technique, giving relevant information to plan the preclinical assessment.

A novel microwave imaging approach to reconstruct the dielectric properties of targets hosted in partially known, noncanonical, scenarios is proposed and assessed. The method takes joint advantage of the recently introduced virtual experiments paradigm and exploits a new linear approximation developed within such a framework. Such an approximation implicitly depends on the unknown targets and, therefore, has a broader applicability as compared with the traditional distorted Born approximation. Being noniterative, the resulting distorted-wave inversion method is capable of quasi-real-time imaging and successfully images nonweak perturbations. The performances of the novel imaging method have been assessed with simulated data and validated experimentally against some of Fresnel data sets.

In this paper, we present an innovative algorithm for sparse imaging of perfect electric conducting (PEC) targets. The algorithm is based on higher order sources or multipoles, rather than zero-order ones as in the standard sparse imaging. We demonstrate that, due to the directivity of higher order sources, the imaging capabilities of the algorithm are enhanced. Particular improvements are achieved when dealing with complex-shaped targets. As a matter of fact, through several illustrative examples, we show that the zero-order sources are more suitable for the reconstruction of the convex parts of target boundaries, whereas the higher order sources are more appropriate for the concave parts of the boundaries. Taking advantage of some analytical considerations in a canonical case, we devise a strategy to select the optimal orders to consider in the imaging procedure without needing any a priori information on the target.

In this contribution, we present a short-radar radar for occupancy sensing and activity discrimination in a through-wall scenario. The system is a continuous wave Doppler radar operating in the S-band of the electromagnetic spectrum to enable a proper radio signal penetration through building walls. The radar signal undergoes a phase modulation produced by human movements and tiny periodic chest displacements associated to respiratory activity. A data processing algorithm is proposed to detect in real-time humans in the scene and provide automatically also an indication on whether they are static or moving. Experimental tests performed in an indoor environment confirm that the proposed sensor and related signal processing provide timely and reliable results.

Foreign body contamination in food is one of the major sources of complaints against food manufacturers, and it can lead to injury, loss of brand loyalty and large recall expenses. Different technologies, such as X-ray or infrared techniques, are currently applied to detection systems used for food inspection, but physical contamination, with e.g. wood, plastic, metal and glass fragments, is still present in food. For this reason, there is the interest to develop new technologies able to address the still unmet needs of food industry. In this paper, we report about preliminary investigations of the use of the microwave imaging technology for food contamination monitoring. Numerical results show the feasibility of the proposed approach. The realization of prototype measurement system is under development.

The aim of this paper is to present and experimentally verify the first prototype of a microwave imaging system specifically designed and realized for the continuous monitoring of patients affected by brain stroke, immediately after its onset and diagnosis. The device is a 2D version of the 3D system, currently under construction, and consists of an array of 12 printed monopole antennas connected to a two-port vector network analyzer through a switching matrix so that each antenna can act as a transmitter or receiver, thereby allowing the acquisition of the entire multistatic multiview scattering matrix required for the imaging. The system has been experimentally tested on 2D phantoms with electric properties mimicking the brain. The presence and the evolution of the stroke have been reproduced by filling a proper cavity in the phantom with a liquid having the electric properties of blood. A differential approach has been adopted by acquiring the scattering matrix before and after the filling of the blood cavity. The so achieved differential dataset has been processed by means of a linear imaging algorithm in order to reconstruct the stroke location and dimension. Moreover, the effect of pre- and postprocessing operations on the measured data is investigated. A good agreement has been obtained between the reconstructions and the actual scenario. As a final remark, it is worth noting that the entire data acquisition and processing are sufficiently fast to allow a real-time monitoring.

International audience; Food quality earns a huge interest from food industry. In particular, the presence of small foreign fragments is generally the main issue in food quality control. While metal contaminants can be detected by means of metal detectors, the same does not happen for plastic or glass pieces. To overcome this limitation, the use of microwave imaging is proposed in this work. The goal is to develop a microwave system to be used along the production chain. To cope with this challenging scenario, in which the measurement time is reduced and only a limited amount of data is available, an imaging strategy taking advantage of the target's movement and of the expected small size of the sought contamination is developed. In this communication, the rationale of the approach is described and assessed in a simple, yet meaningful case.

International audience; In the present work we describe recent developments in the realization of a novel device for monitoring continuously a patient after a cerebrovascular event. The proposed technology is microwave imaging (MWI) exploiting the difference in dielectric properties of ischemic and hemorrhagic areas with respect to the other tissues present in the head. The goal of our work is to realize a prototype device that can be complementary to other imaging techniques, as support for physicians in the choice and control of therapies.

This paper presents advances in the realization of a head phantom dedicated to the test of a microwave imaging system in order to assess its performances in a realistic laboratory controlled configuration before a possible clinical application to brain stroke monitoring. The phantom is based upon a rigid 3D-printed structure that delineates several cavities which can be filled up with different biological tissue mimicking liquid mixtures. The phantom structure and the composition of the tissue mimicking mixtures are detailed and, then, some effects of the differences in dielectric properties between the phantom and a real head on the electric field distribution within the phantom are analyzed through numerical simulations.

The present paper describes our on-going work towards the realization of a novel device to perform continuous monitoring of a patient after a stroke onset. The realization of the antenna array and of the control electronics will be discussed, together with a first experimental test of the system.

The orthogonality sampling method has been recently introduced in inverse scattering literature to perform the reconstruction of the morphological properties of unknown targets. With respect to other qualitative methods, orthogonality sampling shows attractive features, namely the remarkable simplicity and the possibility of being exploited also for a single incidence. However, notwithstanding its straightforwardness and effectiveness, the physical meaning of the method is not yet fully assessed. Since such an understanding would be helpful to take full advantage of its features, in this contribution we present a first attempt to formulate a physical interpretation of the method.

Clinical studies have shown the benefit of hyperthermia as a strong adjuvant to conventional cancer treatments but a tight control of the administered heating still represents an open challenge. Planning the hyperthermia treatment is the way to deliver a target conformal specific absorption rate (SAR) deposition over the target area while keeping the SAR bounded in normal tissue. This task is even more challenging in case of large and irregularly shaped target volumes. Motivated by this need, the so-called multi-target focusing via constrained power optimization was developed. In the current study, we investigated the effective gain in terms of heating profile of the proposed approach using simulations of 3D clinical patient specific models. Results indicate an average median temperature gain of 0.8°C with respect to standard FOCO.

The concept of virtual experiments is based on the idea of solving the inverse scattering problem by processing a suitable recombination of the available data, instead of those arising from the measurements. By properly designing such experiments (and without additional measurements), it is possible to enforce some peculiar field's or contrast source's properties, which can be helpful to perform the inversion in a more simple and reliable way. In this paper, we show that the factorization method can be used as a tool to design the virtual experiments. In doing so, we also provide, for the first time, an insight into its physical meaning. As an example, we exploit the virtual experiments designed via FM as the backbone of a linearized inversion approach for quantitative imaging of non-weak targets.

This chapter provides an introduction to the physical principles underlying the adoption of microwave technology as a biomedical imaging modality for diagnosis and follow-up of neurological diseases and injuries (e.g., stroke, haematoma). In particular, a theoretical analysis, supported by numerical simulations and experiments, will be given to describe the physical constraints that arise in this kind of application and the relevant limitations. In addition, we discuss the main aspects to be faced when implementing microwave imaging technology in a clinical scenario, by exploiting a design procedure to determine the number of antennas needed to capture, in a non-redundant way, the largest part of the available data.

Generating given 3-D field intensity distributions in a non-homogeneous scenario is a canonical problem which is of interest in many applications. On the other side, due to its very challenging nature, very few methods have been proposed up to now in the literature. In this communication, starting from the well-known time reversal (TR) technique, a simple innovative approach, the so-called optimized multi-target TR (O-mt-TR), is presented. The strategy is based on the optimization of the phase shifts between the time-reversed fields in a number of control points within the target region. In doing so, the proposed method outperforms the simple juxtaposition of time-reversed fields pursued by the so-called mt-TR, or even succeed in cases in which the latter fails completely. This capability of the proposed method is assessed through a numerical analysis concerned with a 3-D inhomogeneous scenario, in which the results are quantitatively appraised in terms of coverage of the target areas.

In this paper, we consider the three-dimensional (3D) differential microwave imaging for brain stroke monitoring. Assuming that stroke causes small changes in the electromagnetic parameters of the head, we apply the Distorted Born approximation to linearize the scattering equation. To exploit the sparse nature of the problem, we develop an imaging algorithm based on the compressive sensing. The algorithm was able to locate the stroke and accurately estimate its shape even with limited prior knowledge such as average head permittivity. In addition, we have compared the obtained results with those computed using the truncated singular value decomposition (TSVD).

Microwave imaging can effectively image the evolution of a hemorrhagic stroke thanks to the dielectric contrast between the blood and the surrounding brain tissues. To keep low both the form factor and the power consumption in a bedside device, we propose implementing a microwave imaging algorithm for stroke monitoring in a programmable system-on-chip, in which a simple ARM-based CPU offloads to an FPGA the heavy part of the computation. Compared to a full-software implementation in the ARM CPU, we obtain a 5&times, speed increase with hardware acceleration without loss in accuracy and precision.

In this paper, we present a novel method for microwave imaging using sensors with transverse electric (TE) polarization. The method is applicable to metallic and dielectric objects and exploits the sparseness of the sought solution, by imposing a measurement model based on multipole sources. In order to verify the achievable performance, the method has been numerically tested against different scenarios, including targets with complex concave cross sections as well as multiple objects. The investigation has shown that, opposite to the transverse magnetic (TM) polarization, the standard (zero order) sparse processing yields no or very little information about the targets. In contrast, using higher order multipole sources to build the sparse imaging dictionaries allows retrieving complicated target shapes, even in presence of noise. In addition, we have compared the reconstruction results obtained using the TE and TM polarization.

In this paper, we introduce a simple, noniterative algorithm to estimate the effective dielectric properties of unknown targets from the measurements of their backscattered fields. The proposed approach relies on the virtual experiments concept, as it exploits a combination of the incident fields to be able to focus the exciting field on a certain region. Then, it associates the effective parameters to the permittivity and conductivity values that minimize the mean square error between the virtual scattered field (obtained by recombining the measured data) and the field scattered by a homogeneous dielectric cylinder centered on the target, having approximately the same area. The center of this effective scatterer and its radius can be estimated with a qualitative imaging algorithm or can be given as a priori information. Notably, by properly designing the virtual incident fields, the proposed method can easily handle the case of multiple targets. The effectiveness of the method is assessed by both numerical and experimental examples.

One of the main open challenges in hyperthermia treatment planning is the possibility of uniformly shaping the SAR deposition over a target area, while keeping it bounded in normal tissue. This task is even more challenging as dielectric tissues parameters are prone to uncertainties and targets can be large and irregularly shaped. In this respect, an innovative SAR shaping strategy aimed at addressing the above-mentioned needs, the so-called multi-target focusing via constrained power optimization, has been proposed. This approach has been tested using 3D clinical patient models, exploiting Sim4Life as a simulation platform, and the results show the gain attainable by exploiting the proposed strategy and its robustness in the presence of electromagnetic tissue parameter uncertainties.

This paper presents the design of a novel low-complexity microwave imaging system for monitoring brain stroke. In particular, the design is concerned with the determination of the optimal layout of the antennas array, namely, minimum number, positions, and polarization of the radiating elements, enabling the acquisition of an amount of data such to assure a reliable imaging. This goal is achieved by adopting a rigorous design procedure based on the inspection of the singular value decomposition of the relevant discretized scattering operator and taking into account the actual dynamics and signal-to-noise ratio of the measurement system. The design is first carried out in the case of ideal dipoles and then extended and assessed for actual printed monopole antennas, developed for the imaging system. The resulting system is a helmet equipped with 24 antennas, whose performances have been numerically validated in terms of both spatial resolution and reconstruction capabilities, by employing full-wave numerical simulations, realistic 3-D phantoms of the human head, and an accurate modeling of the actual antennas employed in the system.

The enhancing effect of hyperthermia when combined to radio- and chemio-therapy allow a relevant improvement of such anti-cancer treatments. This communication presents an innovative hyperthermia treatment planning strategy that selectively focus/shape the specific absorption rate deposition within the tumor, while avoiding the unde-sired heating of healthy tissues. This latter represents one of the main therapeutical challenges. Because of its formulation (as a convex programming problem) and the use of multi-frequency applicator, the proposed approach is able to both deliver the global optimal solution of the problem and gather a better control of hot-spots occurrence. The approach is presented for the case of scalar fields, but it is conceptually extendable to vector fields as well.

By taking advantage from the fact that for high conductivity and dielectric scatterers, induced and 'equivalent' currents can be considered localized on the boundary, a new strategy for support reconstruction of both penetrable and impenetrable objects from the measurements of the scattered fields is introduced and described. In particular, an ad hoc sparsity promoting inversion approach is formulated to localize and retrieve the shape of the unknown objects.

Magnetic nanoparticles have been recently proposed as a contrast agent for breast cancer microwave imaging. In this communication, we report on the ongoing activities aiming at the feasibility validation of magnetic nanoparticles enhanced microwave imaging. In particular, we discuss the results of some experiments, carried out to deal with the factors that influence the detection limits of the technique. Previous experiments have shown that a major limitation to the minimum amount of contrast agent that can be appreciated is due to the instrumental drift, which cannot be overcome by simply averaging the measurements. In addition, owing to the low level of the useful signal, possible magnetic effects arising from the system and the involved media can become relevant and impair the measurements. In the following, we deal with these aspects and present the results of a first set of experiments aimed at assessing the detection capabilities of the technique.