The estimation of electrical properties of living biological tissues is relevant to several medical applications ranging from hyperthermia treatment planning to dosimetry and, more in general, is ...pivotal for a fundamental understanding of bioelectromagnetic interactions. Non-invasive electromagnetic imaging, either based on the processing of electric fields measured via microwave tomography or magnetic fields acquired in magnetic resonance is suitable to pursue this goal. In this framework, the possibility of imaging without the need of phase information would be extremely relevant, as it would enable simpler and more reliable devices and would avoid limiting assumptions typically used in the literature. With reference to the canonical yet significant 2D case, in this paper we propose an inverse scattering approach for tissue characterization from only-amplitude electromagnetic data, which, by virtue of a unified mathematical framework, is viable for both microwave tomography and magnetic resonance imaging. The key feature of the method is the innovative use of morphological maps derived by other medical imaging modalities as prior spatial information. In particular, these images are exploited to define a convenient and effective patient-specific representation of the unknowns. The approach is tested against simulated data derived from anatomically realistic scenarios.
Arbitrary shaping the field intensity is a challenging problem relevant in many applications. To date, procedures addressing such a challenging problem have been developed assuming a full knowledge ...of both the scenario and the target within embedded. However, this is not the case in many applications where the investigated scenario is only approximately known and/or modeled on the basis of some auxiliary imaging methods. In this article, we propose a novel adaptive procedure able to shape the field intensity in an unknown (or partially unknown) scenario without the need of a quantitative scenario retrieval. The approach takes advantage from the linear sampling method, which belongs to the class of qualitative imaging methods, in order to focus the field intensity with respect to different control points belonging to the target. Then, the desired spatial field intensity shaping is obtained by recombining the results from such single-focusing problems and by exploiting an additional degree of freedom, which is represented by phase shifts of the field in the considered control points. A preliminary numerical validation and assessment are given for in-homogeneous and lossy unknown 2-D scenarios.
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.
Microwave imaging has been recently proposed as alternative technology for in-line inspection of packaged products in the food industry, thanks to its non-invasiveness and the low-cost of the ...equipment. In this framework, simple and effective detection/imaging strategies, able to reveal the presence of foreign bodies that may have contaminated the product during the packaging stage, are needed to allow real-time and reliable detection, thus avoiding delays along the production line and limiting occurrence of false detections (either negative or positive). In this work, a novel detection/imaging approach meeting these requirements is presented. The approach performs the detection/imaging of the contaminant by exploiting the symmetries usually characterizing the food items. Such symmetries are broken by the presence of foreign bodies, thereby determining a differential signal that can be processed to reveal their presence. In so doing, the approach does not require the prior measurement of a reference, defect-free, item. With respect to the quite common case of homogeneous food packaged in circular plastic/glass jars, numerical analyses are provided to show the effectiveness of the proposed approach.
This paper presents the results of a broadband microwave spectroscopy of a diluted water-based ferrofluid, when subject to an external polarizing magnetic field (PMF) of variable intensity. The ...characterization has been performed exploiting a recently proposed measurement approach, specifically devised to enable accurate measurement of the magnetic properties of such suspensions, properly modified to consider the presence of an applied PMF. To investigate in detail the nature of the response and of its dependence on the applied PMF, the measured susceptibilities have been fitted with a superposition of relaxation and resonance dispersion models. Besides quantitatively assessing results already reported in the literature for similar magnetic nanoparticles (MNPs), but suspended in hydrocarbons the analysis has also led to an unexpected result, namely, the onset of a second ferromagnetic resonance when the PMF exceeds 20 kA/m. Apart from their physical interest, the obtained results provide an accurate and comprehensive characterization of the magnetic response of a class of MNPs exploitable in all the emerging biomedical applications based on the interaction of MNPs and electromagnetic fields, such as microwave imaging.
Quantitative estimation of both conductivity and permittivity of biological tissues is essential in many biomedical applications, ranging from therapeutic treatments to safety assessment of medical ...devices and dosimetry. Typically, the electromagnetic field distribution inside the body is predicted based on available ex-vivo measured electrical properties. Unfortunately, these values may be quite different from the ones measured in-vivo and cannot account for the differences among individuals. As a result, their use can introduce significant errors affecting therapeutic treatments and dose estimation. To cope with this problem, in this paper a new approach for estimation of effective electrical properties of human tissues is introduced. The proposed strategy is based on the solution of an inverse scattering problem (by means of a contrast source inversion scheme) and the use of an effective representation of the unknowns based on spatial priors derived by magnetic resonance imaging or computed tomography. The approach is tested in controlled conditions against simulated single frequency data and realistic and anthropomorphic head and neck phantoms. Moreover, the inherent advantages have been assessed in the framework of hyperthermia treatment planning.
In the food industry, there is a growing demand for cost-effective methods for the inline inspection of food items able to non-invasively detect small foreign bodies that may have contaminated the ...product during the production process. Microwave imaging may be a valid alternative to the existing technologies, thanks to its inherently low-cost and its capability of sensing low-density contaminants. In this paper, a simple microwave imaging system specifically designed to enable the inspection of a large variety of food products is presented. The system consists of two circularly loaded antipodal Vivaldi antennas with a very large operative band, from 1 to 15 GHz, thus allowing a suitable spatial resolution for different food products, from mostly fatty to high water-content foods. The antennas are arranged in such a way as to collect a signal that can be used to exploit a recently proposed real-time microwave imaging strategy, leveraging the inherent symmetries that usually characterize food items. The system is experimentally characterized, and the achieved results compare favorably with the design specifications and numerical simulations. Relying on these positive results, the first experimental proof of the effectiveness of the entire system is presented confirming its efficacy.
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 potential of MR thermometry (MRT) fostered the development of MRI compatible radiofrequency (RF) hyperthermia devices. Such device integration creates major technological challenges and a crucial ...point for image quality is the water bolus (WB). The WB is located between the patient body and external sources to both couple electromagnetic energy and to cool the patient skin. However, the WB causes MRT errors and unnecessarily large field of view. In this work, we studied making the WB MRI transparent by an optimal concentration of compounds capable of modifying T 2 * relaxation without an impact on the efficiency of RF heating. Three different T 2 * reducing compounds were investigated, namely CuSO 4 , MnCl 2 , and Fe 3 O 4 . First, electromagnetic properties and T 2 * relaxation rates at 1.5 T were measured. Next, through multi-physics simulations, the predicted effect on the RF-power deposition pattern was evaluated and MRT precision was experimentally assessed. Our results identified 5 mM Fe 3 O 4 solution as optimal since it does not alter the RF-power level needed and improved MRT precision from 0.39 ∘ C to 0.09 ∘ C. MnCl 2 showed a similar MRT improvement, but caused unacceptable RF-power losses. We conclude that adding Fe 3 O 4 has significant potential to improve RF hyperthermia treatment monitoring under MR guidance.
The success of cancer hyperthermia (HT) treatments is strongly dependent on the temperatures achieved in the tumor and healthy tissues as it correlates with treatment efficacy and safety, ...respectively. Hyperthermia treatment planning (HTP) simulations have become pivotal for treatment optimization due to the possibility for pretreatment planning, optimization and decision making, as well as real-time treatment guidance.
The same computational methods deployed in HTP are also used for in silico studies. These are of great relevance for the development of new HT devices and treatment approaches. To aid this work, 3 D patient models have been recently developed and made available for the HT community. Unfortunately, there is no consensus regarding tissue properties, simulation settings, and benchmark applicators, which significantly influence the clinical relevance of computational outcomes.
Herein, we propose a comprehensive set of applicator benchmarks, efficacy and safety optimization algorithms, simulation settings and clinical parameters, to establish benchmarks for method comparison and code verification, to provide guidance, and in view of the 2021 ESHO Grand Challenge (Details on the ESHO grand challenge on HTP will be provided at
https://www.esho.info/
).
We aim to establish guidelines to promote standardization within the hyperthermia community such that novel approaches can quickly prove their benefit as quickly as possible in clinically relevant simulation scenarios. This paper is primarily focused on radiofrequency and microwave hyperthermia but, since 3 D simulation studies on heating with ultrasound are now a reality, guidance as well as a benchmark for ultrasound-based hyperthermia are also included.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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