Dielectric Properties Of Human Tissues Research Articles

Bio-Interaction Mechanism of Occupational Extremely Low-Frequency Magnetic Field and its Potential Effects on Human

Human lifestyle is evolving as a result of advancement in technology which is mainly driven by electricity. The presence of extremely low frequency magnetic field in the Earth’s atmosphere produced during the processes of generation, transmission and distribution of electricity in occupational environment has the ability to penetrate human skin, and is potentially hazardous to health of exposed individual, which have become a source of concern. This article presents state of knowledge on the electrical and dielectric properties of human tissues, examine the various phenomena processes during the bio-interaction mechanism, all-inclusive biological effects process explained and identify potential health risk associated with prolonged and excessive exposure to occupational magnetic field at extremely low frequency in addition to the underlining factors that influence the probable threats.

Machine learning algorithm to extract properties of ATE phantoms from microwave measurements

Abstract The Muscle Analyzer System (MAS) project wants to create a standalone microwave device that can assess the muscle quality, called the MAS device. To achieve that an algorithm that can derive the properties of skin, fat and muscle from the measurements is needed. This paper presents a machine learning algorithm that aims to do precisely that. The algorithm relies on first predicting the skin using the data from the MAS device, then predicting the fat again using the data from the MAS but also the predicted skin value and lastly the muscle is predicted using the microwave data together with the skin and fat predictions. Data have been collected in phantom experiments, materials that mimick the dielectric properties of human tissues. The algorithm is trained to predict the properties of said phantoms. The results show that the prediction for skin thickness works well, the fat thickness prediction is okay but the muscle prediction struggles. This is partly due to the error from the skin and fat layers are propagated to the muscle layer and partly because the muscle layer is farthest away from the sensor, which makes getting information from that layer harder.

A Fused Learning and Enhancing Method for Accurate and Noninvasive Hydration Status Monitoring With UWB Microwave Based on Phantom

Hydration status is a critical indicator for human health, yet there are relatively few studies on monitoring the hydration status of the human body. Traditional methods for hydration monitoring have shortcomings such as being invasive, time-consuming to detect, and not being real time. Recently, microwave hydration monitoring has attracted research interest widely. This approach is noninvasive and based on the change of dielectric properties of human tissues with different hydration statuses. In this article, a fused learning and enhancing method is proposed to accurately monitor the hydration by using an ultrawideband (UWB) microwave. In the proposed method, an Elman neural network learning model and a joint enhancing method are designed. The joint enhancing algorithm is composed of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$</tex-math> </inline-formula> -medoids and least squares. To verify the performance of the proposed method, a muscle phantom is developed using bovine serum albumin. By changing the concentration, the phantom can mimic the muscle with different hydration statuses. In the evaluation experiment, the S-parameter and frequency data were measured with UWB microwave. Then, the data were employed for assessing the level of hydration with the proposed method. Experimental results showed that the relative error for estimating the concentration of the muscle phantom is less than 3.3%. These results demonstrated the feasibility of the proposed hydration monitoring method and proved that it is promising for monitoring human hydration status.

ANALYSIS OF DIELECTRIC PROPERTIES OF HUMAN TISSUES: RESULTS OF EX VIVO EXPERIMENTS

The aim of the work was to evaluate the dielectric properties of human tissues in ex vivo conditions. The study was performed on 68 tissue samples, 20 of which were fragments of muscle tissue, 17 – fatty, 11 – fibrous and 20 – a full-layer skin flap. The analysis of the dielectric properties of tissue fragments was carried out by the method of near-field resonant microwave sounding using a special software and hardware complex. The study made it possible to verify the presence of pronounced differences in the dielectric properties of tissues depending on their histotype. It was revealed that adipose tissue has the highest level of dielectric permittivity, and fibrous tissue has the lowest one. Muscle tissue and a full-layered skin flap occupy an intermediate position between them. These data are fundamentally important for the creation of standards for the dielectric characteristics of biological objects and the further development of near-field resonant microwave sensing technology as an innovative medical imaging technology.

A heuristic model to evaluate the dielectric properties of human tissues at microwave band based on water and solid content

At the molecular level, the body is composed, on average, of water for 62%, fat for 15%, 17% of protein, and 6% of minerals. In this work, we propose a heuristic methodology using hydration models as a base to realize an automatic and noninvasive procedure to estimate an ad hoc map of the complex dielectric permittivity of a generic human tissue in the frequency range of microwaves based on their solid and water content.

Deep-Implanted MIMO Antenna Sensor for Implantable Medical Devices

A compact multiple-input–multiple-output (MIMO) implantable antenna is proposed in this article for deep-implanted medical devices. The suggested antenna enables high-data-rate telemetry as well as sensing the inner conditions of the tissues. It consists of two semicirc- ular patches that are excited with coaxial cables. The miniaturization in the suggested design is achieved using multiple slots in the patches, shorting pins, and high-permittivity substrate. Consequently, the antenna maintains a compact dimensions of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi \,\,\times6\,\,^{\mathrm{ 2}}\,\,\times0.13$ </tex-math></inline-formula> mm 3. Both elements of the antenna resonate at 0.915 GHz, possess a peak realized gain of −23.23 dBi, and maintain a low mutual coupling of −21.77 dB at 0.915 GHz. The effectiveness of the suggested antenna is verified using the specific absorption rate (SAR) and link budget analysis. Moreover, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${2} \times {2}$ </tex-math></inline-formula> MIMO channel parameters such as the envelope correlation coefficient (ECC), diversity gain (DG), and channel capacity (CC) are calculated. In fact, CC using the suggested antenna reaches to 9.6 bps/Hz at a fixed SNR of 20 dB, which is almost two times more than that of the single-input–single-output (SISO) antenna (CC = 5.89 bps/Hz at SNR = 20 dB). The sensing ability of this antenna is demonstrated in addition to high-data-rate performance. The simulated and measured results confirm that it has almost similar radiation performance, impedance matching, and bandwidths for all dielectric properties of human tissues. Therefore, the proposed antenna is suitable for high-data-rate communication and monitoring pathological changes in deep tissues.

High-resolution probe design for measuring the dielectric properties of human tissues

BackgroundIn order to use the microwave to measure the dielectric constant of the human body and improve the measurement resolution, a small near-field probe working at 915 MHz is designed in this paper.MethodBased on the electric small loop antenna model loaded by the spiral resonator (SR), a small near-field probe was designed. The probe model is designed and optimized by the HFSS (high frequency structure simulator) software. The human tissues were tested by the manufactured probe and the relationship between the S11 parameters of the probe and the human tissues was analyzed.Results and conclusionsA probe with small size was designed and fabricated, with the overall size of 10.0 mm × 12.0 mm × 0.8 mm. The probe has a good performance with a 30.7 dB return loss, a 20 MHz bandwidth at the resonance point, and a distance resolution of 10 mm. Due to the small size and good resolution of the probe, it can be used in the measurement of human tissues.

An investigation on specific absorption rate reduction materials with human tissue cube for biomedical applications

The objective of this study is to investigate the impact of human exposure due to electromagnetic fields and to reduce the specific absorption rate (SAR). This work focuses on the implementation of different electromagnetic shield materials such as conductive materials, dielectric materials, ferrite materials, and metamaterials that are currently used for SAR reduction. The experimental analysis is performed with the global system for mobile communication (GSM) dipole antenna operating at 900 MHz as its radiation source. The designed dipole is placed in front of a cube with similar dielectric properties of human tissue. The computation, implementation, and evaluation are performed by using the method of moments. Further calculation of SAR reduction factor (SRF), SAR 1 g, gain, directivity, and beamwidth are estimated for 15 different shield materials. There is a need for an ideal shield material that could reduce SAR and does not compromise the performance of the radiation structure. This work investigates and proposes the nanomaterials and composites as suitable shield materials for SAR reduction. This novel approach of implementation of nanomaterials has proved to increase the SRF over 90% than conventional reduction materials. In addition, gain and directivity are also increased by 50% than the existing shield materials. The currently used materials are compared with the proposed nanomaterials, and the results are analyzed. The results indicate that the nanomaterials and its composites are ideal shield material for SAR reduction.

Polyvinyl alcohol cryogel phantoms of biological tissues for wideband operation at microwave frequencies.

The aim of this work is to provide a methodology to model the dielectric properties of human tissues based on phantoms prepared with an aqueous solution, in a semi-solid form, by using off-the-shelf components. Polyvinyl alcohol cryogel (PVA-C) has been employed as a novel gelling agent in the fabrication of phantoms for microwave applications in a wide frequency range, from 500 MHz to 20 GHz. Agar-based and deionized water phantoms have also been manufactured for comparison purposes. Mathematical models dependent on frequency and sucrose concentration are proposed to obtain the complex permittivity of the desired mimicked tissues. These models have been validated in the referred bandwidth showing a good agreement to experimental data for different sucrose concentrations. The PVA-C model provides a great performance as compared to agar, increasing the shelf-life of the phantoms and improving their consistency for contact-required devices. In addition, the feasibility of fabricating a multilayer phantom has been demonstrated with a two-layer phantom that exhibits a clear interface between each layer and its properties. Thus, the use of PVA-C extends the option for producing complex multilayer and multimodal phantoms.

Monitoring Thermal Ablation via Microwave Tomography: An Ex Vivo Experimental Assessment.

Thermal ablation treatments are gaining a lot of attention in the clinics thanks to their reduced invasiveness and their capability of treating non-surgical patients. The effectiveness of these treatments and their impact in the hospital’s routine would significantly increase if paired with a monitoring technique able to control the evolution of the treated area in real-time. This is particularly relevant in microwave thermal ablation, wherein the capability of treating larger tumors in a shorter time needs proper monitoring. Current diagnostic imaging techniques do not provide effective solutions to this issue for a number of reasons, including economical sustainability and safety. Hence, the development of alternative modalities is of interest. Microwave tomography, which aims at imaging the electromagnetic properties of a target under test, has been recently proposed for this scope, given the significant temperature-dependent changes of the dielectric properties of human tissues induced by thermal ablation. In this paper, the outcomes of the first ex vivo experimental study, performed to assess the expected potentialities of microwave tomography, are presented. The paper describes the validation study dealing with the imaging of the changes occurring in thermal ablation treatments. The experimental test was carried out on two ex vivo bovine liver samples and the reported results show the capability of microwave tomography of imaging the transition between ablated and untreated tissue. Moreover, the discussion section provides some guidelines to follow in order to improve the achievable performances.

Brain Stroke Microwave Imaging by Means of a Newton-Conjugate-Gradient Method in &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$L^{p}$ &lt;/tex-math&gt; &lt;/inline-formula&gt; Banach Spaces

A conjugate-gradient-based regularization technique in $L^{p}$ Banach spaces, in conjunction with an inexact-Newton solving scheme, is presented in this paper. The proposed method is applied to obtain the reconstruction of the dielectric properties of human tissues in hemorrhagic brain stroke microwave imaging. The dielectric reconstruction is obtained by solving a nonlinear inverse problem, starting from a set of scattered-field measurements. The presented numerical simulations with 2-D and 3-D anatomically realistic phantoms, as well as the preliminary experimental results, show that this method can be useful for retrieving the dielectric properties of the human head with a reduced over-smoothing effect in the final images.

New method for establishing a 3D subject-specific numerical electromagnetic model using hybrid imaging modalities

Numerical electromagnetic models that can mimic the dielectric properties of human tissues have been widely used for dosimetry-related studies in bio-electromagnetics, particularly for the calculation of electromagnetic field distribution inside the human body, which is subject specific. Reports indicated that considerable electromagnetic field variations may occur inside different human subjects even when existing differences in the geometrical dimensions of these subjects are minimal. Therefore, a subject-specific three-dimensional (3D) electromagnetic model is crucially required to calculate the electromagnetic field distribution accurately. However, the manner in which a precise subject-specific 3D electromagnetic model is established has not been fully explored in the literature yet. In this study, a new method was proposed for the establishment of a subject-specific 3D electromagnetic model using hybrid imaging modalities, with computed tomography (CT) and magnetic resonance (MR) images as sources. The exemplary application was provided by using the established subject-specific model to calculate the local specific absorption rates in MR imaging. Comparison studies indicated that detailed information was obtained using the proposed model.

Dielectric Properties Characterization From 0.5 to 50 GHz of Breast Cancer Tissues

Knowledge of the dielectric properties of human tissues is important for several biomedical applications, including imaging and hyperthermia treatment, as well as for determining safety thresholds in policy making. Breast tissues, both normal and tumorous, are of particular interest because of the medical and social impact of breast cancers. While experimental data is available up to 20 GHz, for higher frequencies, this information is missing, or has been extrapolated from models based on lower-frequency data. Emerging technologies and applications in the millimeter-wave region would benefit from experimental data that bridge this gap. This paper presents the characterization of dielectric properties of breast tissues for the frequency range from 0.5 to 50 GHz. Cole–Cole models are derived for normal and tumorous tissues based on experimental measurements on more than 220 tissue samples obtained at surgery ( ex vivo ) from a population exceeding 50 patients, covering a wide span of normal and tumorous tissues, from patients ranging in age from 28 to 85 years, with a time from excision to measurements under 3.5 h. This paper also presents a comprehensive analysis of the differences between normal and tumorous breast tissues at different frequencies in terms of sensitivity and specificity.

MEASURING THE DIELECTRIC PROPERTIES OF TUMOR AND BREAST PHANTOMS USED IN THE MICROWAVE FREQUENCY RANGE

INTRODUCTION: This article deals with measurement of dielectric properties (relative permittivity and conductivity) of phantoms, specifically a tumor phantom and a breast phantom. We focused on the waveguide and resonance methods for the measurement of dielectric properties. The article describes the principle of these methods, and also the production process of a breast phantom and a tumor phantom. These phantoms can be used for measurements in the microwave frequency range, 8–12 GHz.OBJECTIVE: The study’s objective was to design a tumor phantom and a breast phantom, and to measure their dielectric properties. These properties must simulate human tissue.METHODS: To measure dielectric properties of human tissue, phantoms were designed using the waveguide Hippel`s method and the resonance method with a cavity resonator.RESULTS: The aim of this work was to create the phantoms that would have properties comparable to those of real tissues. Results of measurement are shown as frequency dependence of relative permittivity and conductivity for breast, breast phantom, tumor, and tumor phantom.

Heterogeneous breast phantom development for microwave imaging using regression models.

As new algorithms for microwave imaging emerge, it is important to have standard accurate benchmarking tests. Currently, most researchers use homogeneous phantoms for testing new algorithms. These simple structures lack the heterogeneity of the dielectric properties of human tissue and are inadequate for testing these algorithms for medical imaging. To adequately test breast microwave imaging algorithms, the phantom has to resemble different breast tissues physically and in terms of dielectric properties. We propose a systematic approach in designing phantoms that not only have dielectric properties close to breast tissues but also can be easily shaped to realistic physical models. The approach is based on regression model to match phantom's dielectric properties with the breast tissue dielectric properties found in Lazebnik et al. (2007). However, the methodology proposed here can be used to create phantoms for any tissue type as long as ex vivo, in vitro, or in vivo tissue dielectric properties are measured and available. Therefore, using this method, accurate benchmarking phantoms for testing emerging microwave imaging algorithms can be developed.

In-Vivo Time Domain Measurement of Dielectric Properties of Human Body Tissue

It is essential to measure dielectric properties of human tissues for the safety evaluation of electromagnetic field exposures. In this paper, towards developing an in-vivo measurement method for living human tissues, we employed an open-ended coaxial probe together with a time domain reflectometry (TDR) technique, which probably enables us to extract a reflected waveform from some specified tissues in the time domain. We compared the TDR-measured dielectric properties for human surface tissues with those derived from a conventional frequency-domain technique. As a result, we found a fair agreement between them in the frequency range from 300 MHz to 6 GHz. This result suggests the possibility of in-vivo dielectric property measurement for superficial human tissues by using the proposed TDR technique.

Qualitative Analysis of Human Semen Using Microwaves

Microwave engineering now a days plays a vital tool in diagnostic and therapeutic medicine. A quality evaluation of human semen at microwave frequencies using the measurements made at different intervals of time by cavity perturbation technique in the S-band of microwave spectrum is presented in this paper. Semen samples were also examined in the microscopic as well as macroscopic level in clinical laboratory. It is observed that conductivity of semen depends upon the motility of sperm and it increases as time elapses, which finds applications in forensic medicine. Accurate information about the dielectric properties of tissues and biological liquids is important for studies on the biological effects at radio and microwaves frequencies. In macroscopic level, these electrical properties determine the energy deposition patterns in tissue upon irradiation by an electromagnetic field. In microscopic level, they reflect the molecular mechanisms, which underlie the absorption of electromagnetic energy by the tissue or liquids. Knowledge of the microwave dielectric properties of human tissues is essential for the under- standing and development of medical microwave techniques. Microwave thermography, microwave hyperthermia and microwave tomography all rely on processes fundamentally determined by the high frequency electromag- netic properties of human tissues. Tissue temperature pattern retrieval in the microwave thermography is achieved using models of the underlying tissue structure, which depend particularly on the dielectric properties of the tissue (1). A recent review of published data on animal and human dielectric parameters shows that for most tissue types animal measurements are good substitute for human tissues (2). Gabriel etal., Cook and Land etal., reported the dielectric parameters of various human tissues at different RF frequencies.(3-6). Microwave study of human blood using coaxial line and wave-guide methods was carried out by Cook (7). Tissue samples of human brain at microwave frequencies were analysed using sample cell terminated transmission line methods (8). Open-ended coaxial line method allows measurements of tissue samples over a wide range of frequencies (9). Microwave medical tomography is emerging as a novel non-hazardous method of imaging for the detection of fracture, swelling and diagnosis of tumors. Active and passive microwave imaging for disease detection and treatment monitoring require proper knowledge of body tissue dielectric properties at the lower microwave frequencies (10-12). Studies on the variation of dielectric properties of body fluids and urinary calcifications at microwave frequencies have revealed that diagnosis is possible through cavity perturbation technique (13-15). The present paper reports dielectric properties of semen at microwave frequencies as well as the quantitative analysis in the clinical laboratory. It is observed that conductivity of semen depends upon the motility of sperm as well as the time elapses after ejaculation. 2. Materials and Methods The experimental set-up consists of a transmission type S-band rectangular cavity resonator, HP 8714 ET network analyser. The cavity resonator is a transmission line with one or both ends closed. The resonant frequencies are determined by the length of the resonator. The resonator in this set-up is excited in the TE10� mode. The sample holder which is made of glass in the form of a capillary tube flared to a disk shaped bulb at the bottom is placed into the cavity through the non-radiating cavity slot, at broader side of the cavity which can facilitate the easy movement of the holder. The resonant frequency fo and the corresponding quality factor Qo of the cavity at each resonant peak with the empty sample holder placed at the maximum electric field are noted. The same holder filled with known amount of sample under study is again introduced into the cavity resonator through the non-radiating slot. The resonant frequencies of the sample loaded cavity is selected and the position of the sample is adjusted for maximum perturbation (i.e., maximum shift of resonant frequency with minimum amplitude for the peak). The new resonant frequency fs and the quality factor Qs are noted. The same procedure is repeated for other resonant frequencies.

Derivation of extracellular fluid volume fraction and equivalent dielectric constant of the cell membrane from dielectric properties of the human body. Part 1: Incorporation of fat tissue into cell suspension model in the arm.

The non-invasive characterisation of cell pathophysiology is clinically important. A cell suspension model is applied to derive the extracellular fluid (ECF) volume fraction and the equivalent dielectric constant of the cell membrane epsilon m from the dielectric properties of human arms. Frequency-dependent dielectric constants and electrical conductivities of arms are obtained from 35 surgical patients over a frequency range of 5-1000 kHz. The cell suspension model is applied to fit the data using a complex non-linear least-squares method. The arms show typical dielectric dispersions, although the cell suspension model yields a poor fitting in dielectric constants at lower frequencies and electrical conductivities at higher frequencies. In contrast, a new cell suspension model, taking into account the fat tissue component, remarkably improves the overall fitting performance, allowing estimation of the volume fractions of ECF (0.34 +/- 0.05) and fat tissue (0.16 +/- 0.04) and the equivalent epsilon m (23 +/- 9). The resulting estimates of the volume fraction of fat tissue are in good correlation with arm skinfold thickness (fat volume fraction of arm = 2.42 x 10(-3) x arm skinfold thickness (mm) + 0.099, R = 0.756, p < 0.0001). Therefore it is concluded that the newly derived cell suspension model is well suited for the description of the dielectric properties of human tissues and thus the derivation of the ECF volume fraction and equivalent epsilon m.

Dielectric measurements on reference liquids using automatic network analysers and calculable geometries

Knowledge of the in vivo dielectric properties of human tissues is essential to the development of biomedical techniques which make use of radiofrequency and microwave radiation. The sensors used for measurement of tissue properties can be conveniently calibrated using dielectric reference liquids, but this in turn requires that the dielectric properties of such liquids be accurately known. Many complex permittivity measurements on suitable liquids, such as the primary alcohols and saline solutions, have been reported in the literature, but unfortunately there are in some cases significant discrepancies between reported values. The authors describe a program of work undertaken to resolve some of these anomalies. A number of techniques which make use of 14 mm coaxial cells and sensors coupled to an automatic network analyser are under investigation. Comparison of the different techniques should facilitate evaluation of systematic uncertainties. The liquid measurement geometries and the associated computational methods are described. Details are given of the uncertainty analysis, and examples of mappings from the complex permittivity plane on to the scattering coefficient plane are shown. Some preliminary results are presented, which highlight the value of the comparative approach that has been adopted.

Dielectric properties of gelatine phantoms used for simulations of biological tissues between 10 and 50 MHz.

The use of gelatine phantoms for simulating the dielectric properties of human tissues is suggested. These phantoms are mainly made of gelatine and water and are therefore readily prepared at a low cost. They can be poured into moulds and adopt various shapes depending on the organ to be simulated. In addition, their preservation is not critical. We have studied, at 10, 27 and 50 MHz, the variations of relative permittivity and conductivity as a function of temperature between 15 and 50 degrees C. What is shown is that those values vary both as a function of gelatine concentrations and as a function of temperature. For example, at 37 degrees C and 27 MHz, variations of relative permittivity from 87 to 100 and variations of the conductivity from 0.27 to 0.45 S/m for concentrations of 10% to 40% are observed. At the above frequency, the permittivity of human and animal tissues range between 95 and 180 and the conductivity between 0.4 and 0.6 S/m. Furthermore, the addition of sodium chloride at variable concentrations enables both conductivity and permittivity values to be modified. We propose, as 'muscle-equivalent' phantoms at 27 MHz, a phantom consisting of 20% gelatine with an electrical conductivity from 0.27 to 0.48 S/m and a relative permittivity from 90 to 93 at temperatures between 15 and 50 degrees C. These gelatine, water and sodium chloride phantoms are adapted for easy and cheap simulation of most human tissues in a temperature range from 15 to 50 degrees C, for frequencies from 10 to 50 MHz.