1,196 research outputs found

    Dielectric properties of colon polyps, cancer, and normal mucosa: Ex vivo measurements from 0.5 to 20 GHz

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    This is the accepted version of the following article: Guardiola, M. , Buitrago, S. , Fernández‐Esparrach, G. , O'Callaghan, J. M., Romeu, J. , Cuatrecasas, M. , Córdova, H. , González Ballester, M. Á. and Camara, O. (2018), Dielectric properties of colon polyps, cancer, and normal mucosa: Ex vivo measurements from 0.5 to 20 GHz. Med. Phys., 45: 3768-3782. doi:10.1002/mp.13016, which has been published in final form at https://aapm.onlinelibrary.wiley.com/doi/pdf/10.1002/mp.13016. This article may be used for non-commercial purposes in accordance with the Wiley Self-Archiving Policy [http://olabout.wiley.com/WileyCDA/Section/id-820227.html].Colorectal cancer is highly preventable by detecting and removing polyps, which are the precursors. 20 Currently, the most accurate test is colonoscopy, but still misses 22% of polyps due to visualization limitations. In this paper we preliminary assess the potential of microwave imaging and dielectric properties (e.g. complex permittivity) as a complementary method for detecting polyps and cancer tissue in the colon. The dielectric properties of biological tissues have been used in a wide variety of applications, including safety assessment of wireless technologies and design of medical diagnostic or therapeutic techniques 25 (microwave imaging, hyperthermia and ablation). The main purpose of this work is to measure the complex permittivity of different types of colon polyps, cancer and normal mucosa in ex vivo human samples to study if the dielectric properties are appropriate for classification purposes.Peer ReviewedPostprint (author's final draft

    Electromagnetic Nondestructive Evaluation of Wire Insulation and Models of Insulation Material Properties

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    Polymers have been widely used as wiring electrical insulation materials in space/air-craft. The dielectric properties of insulation polymers can change over time, however, due to various aging processes such as exposure to heat, humidity and mechanical stress. Therefore, the study of polymers used in electrical insulation of wiring is important to the aerospace industry due to potential loss of life and aircraft in the event of an electrical fire caused by breakdown of wiring insulation. Part of this research is focused on studying the mechanisms of various environmental aging process of the polymers used in electrical wiring insulation and the ways in which their dielectric properties change as the material is subject to the aging processes. The other part of the project is to determine the feasibility of a new capacitive nondestructive testing method to indicate degradation in the wiring insulation, by measuring its permittivity

    Soil Moisture Sensing via Swept Frequency Based Microwave Sensors

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    There is a need for low-cost, high-accuracy measurement of water content in various materials. This study assesses the performance of a new microwave swept frequency domain instrument (SFI) that has promise to provide a low-cost, high-accuracy alternative to the traditional and more expensive time domain reflectometry (TDR). The technique obtains permittivity measurements of soils in the frequency domain utilizing a through transmission configuration, transmissometry, which provides a frequency domain transmissometry measurement (FDT). The measurement is comparable to time domain transmissometry (TDT) with the added advantage of also being able to separately quantify the real and imaginary portions of the complex permittivity so that the measured bulk permittivity is more accurate that the measurement TDR provides where the apparent permittivity is impacted by the signal loss, which can be significant in heavier soils. The experimental SFI was compared with a high-end 12 GHz TDR/TDT system across a range of soils at varying soil water contents and densities. As propagation delay is the fundamental measurement of interest to the well-established TDR or TDT technique; the first set of tests utilized precision propagation delay lines to test the accuracy of the SFI instrument’s ability to resolve propagation delays across the expected range of delays that a soil probe would present when subjected to the expected range of soil types and soil moisture typical to an agronomic cropping system. The results of the precision-delay line testing suggests the instrument is capable of predicting propagation delays with a RMSE of +/−105 ps across the range of delays ranging from 0 to 12,000 ps with a coefficient of determination of r2 = 0.998. The second phase of tests noted the rich history of TDR for prediction of soil moisture and leveraged this history by utilizing TDT measured with a high-end Hewlett Packard TDR/TDT instrument to directly benchmark the SFI instrument over a range of soil types, at varying levels of moisture. This testing protocol was developed to provide the best possible comparison between SFI to TDT than would otherwise be possible by using soil moisture as the bench mark, due to variations in soil density between soil water content levels which are known to impact the calibration between TDR’s estimate of soil water content from the measured propagation delay which is converted to an apparent permittivity measurement. This experimental decision, to compare propagation delay of TDT to FDT, effectively removes the errors due to variations in packing density from the evaluation and provides a direct comparison between the SFI instrument and the time domain technique of TDT. The tests utilized three soils (a sand, an Acuff loam and an Olton clay-loam) that were packed to varying bulk densities and prepared to provide a range of water contents and electrical conductivities by which to compare the performance of the SFI technology to TDT measurements of propagation delay. For each sample tested, the SFI instrument and the TDT both performed the measurements on the exact same probe, thereby both instruments were measuring the exact same soil/soil-probe response to ensure the most accurate means to compare the SFI instrument to a high-end TDT instrument. Test results provided an estimated instrumental accuracy for the SFI of +/−0.98% of full scale, RMSE basis, for the precision delay lines and +/−1.32% when the SFI was evaluated on loam and clay loam soils, in comparison to TDT as the bench-mark. Results from both experiments provide evidence that the low-cost SFI approach is a viable alternative to conventional TDR/TDT for high accuracy applications

    Thermal degradation of biological DNA studied by dielectric spectroscopy

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    Dielectric spectroscopy was tested as an alternative tool to study degradation of deoxyribonucleic acid (DNA) in its solid form. The specimens, prepared from biological DNA, were periodically heated and cooled according to a programmed scheme. Simultaneously, their dielectric parameters (permittivity and dielectric loss) were monitored as function of frequency and temperature. The analysis of Bode plots allowed to determine the upper limit of thermal stability of solid DNA at 120 °C, because heating at higher temperatures resulted in irreversible changes. These changes were identified as denaturation by gel electrophoresis and UV–vis absorption methods

    An Investigation of Radiometer and Antenna Properties for Microwave Thermography

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    Microwave thermography obtains information about the subcutaneous body temperature by a spectral measurement of the intensity of the natural thermally generated radiation emitted by the body tissues. At lower microwave frequencies the thermal radiation can penetrate through biological tissue for significant distances. The microwave thermal radiation from inside the body can be detected and measured non-invasively at the skin surface by the microwave thermography technique, which uses a radiometer to measure the radiation which is received from an antenna on the skin. In the microwave region the radiative power received from a volume of material has a dependence on viewed tissue temperature T(r) of the form, where k is the Boltzmann's constant, B the measurement bandwidth, c(r) is the relative contribution from a volume element dv (the antenna weighting function). The weighting function, c(r), depends on the structure and the dielectric properties of the tissue being viewed, the measurement frequency and the characteristics of the antenna. In any practical radiometer system the body microwave thermal signal has to be measured along with a similar noise signal generated in the radiometer circuits. The work described in this thesis is intended to lead to improvement in the performance of microwave thermography equipment through investigations of antenna weighting functions and radiometer circuit noise sources. All work has been carried out at 3.2 GHz, the central operating frequency of the existing Glasgow developed microwave thermography system. The effects of input circuit losses on the operation of the form of Dicke radiometer used for the Glasgow equipment have been investigated using a computational model and compared with measurements made on test circuits. Very good agreement has been obtained for modelled and measured behaviour. The losses contributed by the microstrip circuit structure, that must be used in the radiometer at 3.2 GHz, have been investigated in detail. Microwave correlation radiometry, by "add and square" method, has been applied to the received signals from a crossed-pair antenna arrangement, the antennas being arranged to view a common region at a certain depth. The antenna response has been investigated using a noise source and by the nonresonant perturbation technique. The received pattern formed by the product of the individual antenna patterns gives a maximum depth in phantom dielectric material. The depth can be adjusted by changing the spacing of the antennas and the phase in an antenna path. However, the pattern is modulated by a set of positive and negative interference fringes so that the complete receive pattern has a complicated form. On uniform temperature distributions the total radiometric signal is zero with the positive and negative contributions cancelling each other out. The fringe modulation can be removed by placing the antennas close enough together, The pattern is then simple and gives a modest maximum response at a known depth in a known material. The radiometer system remains sensitive to the temperature gradients only and the wide range of dielectric properties and tissue structures in the region being investigated usually makes the system response difficult to interpret. For crossed-pair antennas in phase the effective penetration depth in high-and medium-water content tissues is about 2.5 cm at a frequency of 3.2 GHz. The field pattern observed was of the form expected from the measurements of the individual antenna behaviour with the appropriate interference pattern superimposed. The nonresonant perturbation technique has been developed and applied to assist the development of the medical application of both microwave thermographic temperature measurement and microwave hyperthermia induction. These techniques require the electromagnetic field patterns of the special antennas used to be known. These antennas are often formed by short lengths of rectangular or cylindrical waveguide loaded with a low-loss dielectric material to achieve good coupling to body tissues. The high microwave attenuation in biological materials requires the field configurations to be measured close to the antenna aperture in the near-field wave. The nonresonant perturbation is a simple technique which can be used to measure electromagnetic fields in lossy material close to the antenna. It has been applied here to measure accurately the antenna weighting function and the effective penetration depth in tissue simulating dielectric phantom materials. (Abstract shortened by ProQuest.)

    Antenna and system design for controlled delivery of microwave thermal ablation

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    Doctor of PhilosophyDepartment of Electrical and Computer EngineeringPunit PrakashMicrowave ablation is an established minimally invasive modality for thermal ablation of unresectable tumors and other diseases. The goal of a microwave ablation procedure is to deliver microwave power in a manner localized to the targeted tissue, with the objective of raising the target tissue to ablative temperatures (~60 °C). Engineering efforts in microwave applicator design have largely been focused on the design of microwave antennas that yield large, near-spherical ablation zones, and can fit within rigid needles or flexible catheters. These efforts have led to significant progress in the development and clinical application of microwave ablation systems, particularly for treating tumors in the liver and other highly vascular organs. However, currently available applicator designs are ill-suited to treating targets of diverse shapes and sizes. Furthermore, there are a lack of non-imaging-based techniques for monitoring the transient progression of the ablation zone as a means for providing feedback to the physician. This dissertation presents the design, implementation, and experimental evaluation of microwave ablation antennas for site-specific therapeutic applications with these issues in mind. A deployable 915 MHz loop antenna is presented, providing a minimally-invasive approach for thermal ablation of the endometrial lining of the uterus for treatment of heavy menstrual bleeding. The antenna incorporates a radiating loop, which can be deployed to adjustable shapes within the uterine cavity, and a passive element, to enable thermal ablation, to 5.7–9.6 mm depth, of uterine cavities ranging in size from 4–6.5 cm in length and 2.5–4.5 cm in width. Electromagnetic–bioheat transfer simulations were employed for design optimization of the antennas, and proof-of-concept applicators were fabricated and extensively evaluated in ex vivo tissue. Finally, feasibility of using the broadband antenna reflection coefficient for monitoring the ablation progress during the course of ablation was evaluated. Experimental studies demonstrated a shift in antenna resonant frequency of 50 MHz correlated with complete ablation. For treatment of 1–2 cm spherical targets, water-cooled monopole antennas operating at 2.45 and 5.8 GHz were designed and experimentally evaluated in ex vivo tissue. The technical feasibility of using these applicators for treating 1–2 cm diameter benign adrenal adenomas was demonstrated. These studies demonstrated the potential of using minimally-invasive microwave ablation applicators for treatment of hypertension caused by benign aldosterone producing adenomas. Since tissue dielectric properties have been observed to change substantially at elevated temperatures, knowledge of the temperature-dependence of tissue dielectric properties may provide a means for estimating treatment state from changes in antenna reflection coefficient during a procedure. The broadband dielectric properties of bovine liver, an established tissue for experimental characterization of microwave ablation applicators, were measured from room temperature to ablative temperatures. The measured dielectric data were fit to a parametric model using piecewise linear functions, providing a means for readily incorporating these data into computational models. These data represent the first report of changes in broadband dielectric properties of liver tissue at ablative temperatures and should help enable additional studies in ablation system development

    Application of microwave sensors to potato products

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    The first microwave measurement techniques uses an open ended coaxial probe with a purposely built sample holder to measure the dielectric properties of potato products from 500 MHz to 1 GHz. The second system utilises a waveguide cell with a purposely built sample holder to characterise potato products from 2.4 to 3.5 GHz. Common British varieties of raw potatoes such as Estima, King Edward and Maris Piper are used in this study. The two microwave measurement techniques are also used to measure the dielectric properties of potato products at elevated temperatures for these frequency ranges. Both measurement techniques are also used to study the effect of storage temperature on the dielectric properties of Saturna raw potato. For this part of the study, it is concluded that the microwave measurement techniques are unable to discriminate between potatoes that had a storage history of different temperature profiles. On the other hand, waveguide cells and open ended coaxial probes are able to measure the dielectric properties of raw potato, partial cooked fried potato and fried potato at the 500 MHz to 1 GHz and 2.4 GHz to 3.5 GHz frequency range. The measurement results show that both dielectric constant and loss values of fried potatoes decreased with frying time, due to the reduced moisture content during the frying process. Furthermore, the dielectric loss behaviour of raw and fried potatoes is dominated by the effect of the ionic conductivity at frequencies lower than 1 GHz. An apparatus has been designed and built in order to measure the dielectric properties of potato for both frequency ranges as a function of temperature. In the subsequent measurements it is found that the dielectric properties of potato products at elevated temperatures also depend on frequency and moisture content. For high moisture content potato (~> 70 %), at 2.45 GHz both the dielectric constant and loss are found to decrease with temperature, whereas at 915 MHz the dielectric constant decreases but the loss increases for the moisture content above 30%. For the intermediate moisture content (10%<MC<70%), all dielectric properties increase with temperature at the microwave heating frequencies 2.45GHz, whereas at 915 MHz all the dielectric properties increase with temperature for the moisture content range 10% to 30%. The increase in dielectric properties with temperature is small and marginal for fried potatoes with low moisture content (< 10 %). It is therefore apparent that moisture content is the primary factor in detecting the complex permittivity of potato products.EThOS - Electronic Theses Online ServiceMARDIGBUnited Kingdo

    Spin resonance excitation of Gd-based contrast agents for thermal energy deposition

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    A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2016The theoretical and experimental investigation of electron spin-resonance relaxation to deposit thermal energy into liquid gadolinium-based contrast agents for cancer hyperthermia treatment is presented. Previous works suggest that using protons in water are inadequate, with a thermal deposition rate of approximately 1 ◦C per two years. A novel component of this research relies on the use of gadolinium-chelated molecules, which are currently used as contrast agents in clinical MRI scans. The chelating agents, or ligands, investigated are Gadobenate (MultiHance R ), Gadopentetate (Magnevist R ), Gadoterate (DotaremR ) and Gadoteridol (ProHance R ). The gadolinium atom has seven unpaired electrons in its inner f shell orbital and as a result has a 660 times stronger paramagnetic response when placed in an external magnetic field. The research tests the hypothesis that by using an appropriate external homogeneous DC magnetic field, together with a radiofrequency excited resonator, that a measurable amount of thermal energy is deposited into a liquid gadolinium-based contrast agent. The aim of this research is to ultimately discover a new cancer hyperthermia treatment. The research theory suggests that a temperature rate of 13.4 ◦C · s−1 can be achieved using the gadolinium-based contrast agents under certain experimental conditions, and a maximum of 29.4 ◦C · s−1 under more optimal conditions. The temperature rates are calculated using parameter values commonly found in literature and practice. The simulation and design of the DC magnetic field coil system is discussed, together with the simulation results and design parameters of the radiofrequency loop-gap resonator. The experimental results and analysis indicate that the selected contrast agents have varied responses based on their chemical nature and that only two out of the four contrast agents, Dotarem and ProHance, show a measurable effect albeit sufficiently small that statistical techniques were necessary to distinguish the effect from background. A model fit to the data is performed in order to determine the spin-lattice relaxation time of the contrast agents under the specified experimental conditions. The model estimate is significantly smaller than the values found in literature under similar conditions, with a spin-lattice relaxation time τ1e of approximately 0.2 ps compared to the literature value of 0.1 ns. Although the observed electron spin resonance heating rate is in the milli-Watt range it is still notably larger (167 000 times) compared to the heating rate obtained using protons. The low temperature rates suggest that a more suitable agent or molecule with a larger spin-relaxation time be used, in order to achieve clinical useful temperature rates in the range of 14 ◦C · s−1.MT201

    암 진단 및 치료에 적용 가능한 마이크로파 능동 집적 탐침에 관한 연구

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    학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 2. 권영우.본 논문에서는 암 진단 및 치료에 적용 가능한 초소형 마이크로파 능동 집적 탐침에 대해 기술하였다. 생체 조직의 광대역 측정과 저전력 온열 치료에 적용 하기 위해 유전율 측정 회로를 평면형 동축 탐침에 집적하였고, 마이크로파 발생 회로를 어플리케이터에 집적하였다. MEMS 기술과 MMIC 기술을 적용함으로써 단일 플랫폼에 집적된 시스템으로 구현하여 집적도를 향상 시키고, 시스템을 소형화 하였다. 먼저 multi-state reflectometer를 이용하여 암 진단에 활용 가능한복소 유전율 측정 기술에 대해 제안하였다. 2, 16 GHz에서 동작하는 광대역 reflectometer는 이중 대역 위상 고정 루프 (PLL), 임피던스 튜너, RF 전력 검출기 등의 MMIC와 MEMS 기반의 방향성 결합기, 평면형 탐침을 집적하여 구현하였다. 제작한 능동 집적 탐침 시스템을 이용하여 생체 조직과 암 조직 등의 유전율을 측정함으로써 유용함을 확인하였고, 측정된 유전율과 표준값을 비교하여 시스템의 측정 정확도를 검증하였다. 또한 저전력 마이크로파 온열 치료 요법을 위한 능동 집적 탐침을 개발하였다. MEMS 공정을 통해 제작한 평면형 실리콘 탐침에 전압 제어 발진기, 구동 증폭기, 전력 증폭기를 집적하여 능동 집적 탐침 시스템을 제작하였다. 치료를 진행하는 동안, 마이크로파의 전력을 측정할 수 있도록 전력 검출기와 방향성 결합기도 함께 집적하였다. 암, 근육 등 다양한 생체 조직을 이용한 실험의 결과로부터 Ku 대역의 주파수에서 저전력 마이크로파 온열 치료가 가능함을 확인하였다. 마지막으로 자성 나노입자를 이용한 온열 치료에 적용하기 위해 능동 집적 탐침을 개발하였다. 자성 나노입자가 온열 치료 요법에 미치는 영향을 분석하기 위해 전자기-열 결합 해석을 수행하였고, 이로부터 자성 나노입자의 선택도 향상을 위한 최적의 주파수를 결정하였다. 발진기와 전력 증폭기 MMIC와 이중 채널 로그 전력 검출기, 방향성 결합기를 탐침에 집적하여 시스템을 제작하였다. 이를 이용한 실험 결과로부터 능동 집적 탐침의 성능을 확인하였으며, 자성 나노입자가 저전력 및 암 특이 마이크로파 온열 치료의 효율과 선택도를 향상시키는데 유용함을 검증하였다.This thesis presents miniaturized microwave active integrated probe systems applicable to cancer detection and treatment. To realize broadband detection and low-power hyperthermia, planar-type coaxial probes and heat applicators have been integrated with active circuits for permittivity measurement and microwave generation, respectively. Each integrated system is implemented on a single platform using Microelectromechanical Systems (MEMS) and monolithic microwave integrated circuit (MMIC) technologies for miniaturization and integration. First, a complex permittivity measurement technique using an integrated multi-state reflectometer (MSR) is proposed for cancer detection application. The broadband MSR covering both 2 and 16 GHz bands consists of a dual-band phase-locked loop, a directional coupler, an impedance tuner, two RF power detectors, and a micromachined silicon planar probe with an open-ended coaxial aperture. All the active and passive circuit components have been integrated on the micromachined probe platform in a small form factor of 6.8 mm × 50 mm × 0.6 mm. The performance of the fabricated integrated probe has been evaluated by comparing the measured permittivities of 0.9% saline, pork muscle, fat, and xenografted human breast cancer with the reference data. For low-power microwave hyperthermia, a Ku-band active integrated heat applicator is demonstrated. A planar-type coaxial applicator has been fabricated using silicon micromachining technology, on which a Ku-band voltage controlled oscillator (VCO), a driver amplifier, and a power amplifier (PA) have been integrated. A directional coupler and power detectors are employed for power monitoring. The fully integrated heat applicator has been realized in a small footprint of 8 mm × 56 mm. In-vitro and in-vivo ablation experiments on pork muscle, fat, and human-cancer xenografted nude mouse demonstrate the feasibility of low-power hyperthermia using Ku-band microwaves. Finally, an active integrated heat applicator for magnetic nanoparticle (MNP)-assisted hyperthermia is developed. The effect of the MNP on microwave hyperthermia has been analyzed by a coupled electromagnetic-thermal analysis. The optimum frequency for hyperthermia is determined by the coupled analysis. A 2-GHz source module consisting of a VCO and a PA has been implemented in MMICs and integrated on the heat applicator platform. A dual-channel log detector and a directional coupler have been also employed to monitor the power levels during hyperthermia. Experiment results show not only sufficient heating performance of the integrated applicator, but also the effectiveness of the MNP for low-power and cancer-specific microwave hyperthermia.Abstract i Contents iv List of Figures viii List of Tables xv 1. Introduction 1 1.1 Motivation 1 1.2 Microwave Cancer Detection 4 1.3 Microwave Hyperthermia 5 1.4 Outline of Thesis 7 2. Active Integrated Probe for Cancer Detection 9 2.1 Introduction 9 2.2 Principle of Operation 13 2.2.1 Multi-State Reflectometer 14 2.2.2 Governing Equation for Complex Permittivity 15 2.2.3 Determination of Complex Permittivity 17 2.2.4 Calibration 19 2.3 Design and Fabrication 21 2.3.1 Micromachined Planar Coaxial Probe 21 2.3.2 Impedance Tuner 30 2.3.3 Directional Coupler 34 2.3.4 Power Detector 37 2.3.5 Signal Source 39 2.3.6 Active Integrated Probe System 43 2.4 Measurement Results 46 2.5 Summary 52 3. Ku-Band Active Integrated Heat Applicator for Cancer Ablation 54 3.1 Introduction 54 3.2 Design and Fabrication 57 3.2.1 Micromachined Planar Coaxial Applicator 58 3.2.2 Microwave Source 63 3.2.3 Power Monitoring Circuits 67 3.2.4 Ku-Band Active Integrated Applicator System 67 3.3 Experiment Results 70 3.4 Summary 77 4. Active Integrated Heat Applicator for Magnetic Nanoparticle-Assisted Hyperthermia 79 4.1 Introduction 79 4.2 Magnetic Nanoparticle (MNP) 82 4.2.1 Heating mechanism of MNP 83 4.2.2 Permeability of MNP 84 4.3 Coupled Electromagnetic-Thermal Analysis 88 4.3.1 Coupled Electromagnetic-Thermal Problems 88 4.3.2 Electromagnetic Analysis 92 4.3.3 Thermal Analysis 94 4.3.4 Analysis Results 96 4.4 Design and Fabrication 103 4.4.1 Spiral Applicator 104 4.4.2 Microwave Source 107 4.4.3 Power Monitoring Circuits 111 4.4.4 Active Integrated Applicator for MNP-Assisted Hyperthermia 119 4.5 Experiment Results 122 4.6 Summary 132 5. Conclusion 134 Bibliography 137 Abstract in Korean 152Docto
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