Factors affecting the 13.56-MHz radio-frequency-mediated heating of gold nanoparticles
Paul PantanoCheri D. HarrisonJohn PouloseDavid UrrabazoTrevor Q. NormanElizabeth I. BraunRockford K. DraperLawrence Overzet
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The use of radio-frequency (RF) energy for the thermal activation of tumor-targeted nanoparticles (NPs) is a promising non-invasive hyperthermic treatment because RF waves penetrate deep through tissue. Nonetheless, while the approach has been demonstrated using gold (Au) and iron oxide NPs, the RF-mediated heating mechanism of AuNPs has been controversial. A part of the reason is that measuring and modeling the heating of AuNPs in an RF field is a complex endeavor that depends on the chemical and physical properties of the AuNPs, interfacial phenomena involving AuNP coatings and the sample medium, and the antenna design and characteristics of the RF field. Herein, the mechanisms and factors affecting the 13.56-MHz RF-mediated heating of AuNPs are reviewed, a new factor concerning the thermal isolation of RF antennae is presented, and the ability of a new water-free cooling system to thermally isolate samples from the heat generated by metal RF-induction coils is demonstrated.Keywords:
Induction Heating
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RF probe
During the TTF-FEL Phase I, the RF gun of the TESLA Test Facility (TTF) has been operated with long RF pulses (up to 0.9 ms) and high RF peak power (up to 3 MW). RF breakdowns have been observed and localized in the RF input coupler. In this report we will present statistics of RF breakdowns for different RF pulse length, peak power and repetition rates from 0.1 Hz to 2 Hz. We will also discuss the origin of these breakdowns.
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The sensitivity gain of ultrahigh field Magnetic Resonance (UHF-MR) holds the promise to enhance spatial and temporal resolution. Such improvements could be beneficial for cardiovascular MR. However, intracoronary stents used for treatment of coronary artery disease are currently considered to be contra-indications for UHF-MR. The antenna effect induced by a stent together with RF wavelength shortening could increase local radiofrequency (RF) power deposition at 7.0 T and bears the potential to induce local heating, which might cause tissue damage. Realizing these constraints, this work examines RF heating effects of stents using electro-magnetic field (EMF) simulations and phantoms with properties that mimic myocardium. For this purpose, RF power deposition that exceeds the clinical limits was induced by a dedicated birdcage coil. Fiber optic probes and MR thermometry were applied for temperature monitoring using agarose phantoms containing copper tubes or coronary stents. The results demonstrate an agreement between RF heating induced temperature changes derived from EMF simulations versus MR thermometry. The birdcage coil tailored for RF heating was capable of irradiating power exceeding the specific-absorption rate (SAR) limits defined by the IEC guidelines by a factor of three. This setup afforded RF induced temperature changes up to +27 K in a reference phantom. The maximum extra temperature increase, induced by a copper tube or a coronary stent was less than 3 K. The coronary stents examined showed an RF heating behavior similar to a copper tube. Our results suggest that, if IEC guidelines for local/global SAR are followed, the extra RF heating induced in myocardial tissue by stents may not be significant versus the baseline heating induced by the energy deposited by a tailored cardiac transmit RF coil at 7.0 T, and may be smaller if not insignificant than the extra RF heating observed under the circumstances used in this study.
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Abstract The article contains sections titled: 1. Introduction 2. Resistance Heating 2.1. Direct Resistance Heating of Electrically Conducting Materials 2.2. Indirect Resistance Heating of Materials 3. Infrared Heating 4. Induction Heating 4.1. Direct Induction Heating of Metals 4.2. Indirect Induction Heating of Materials 5. Dielectric Heating of Nonmetals 6. Thermal Plasma Heating 7. Electron Beam Heating 8. Laser Heating
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Induction and dielectric heating have assumed in recent years an important position in industrial heating; dielectric heating more recently than induction. These unique forms of heating, once responsible only for power losses in electric equipment and machinery, offer many advantages over conventional means of heating by convection, conduction, and radiation. The field of application is very broad because induction heating is suited to metals, particularly those that have a high magnetic permeability, and dielectric heating may be accomplished in a large class of thermally insulating materials which at low frequencies are also electrically insulating.
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RF power amplifier efficiency and power output can be measured accurately without an RF power meter. The authors transfer to DC the measurement of RF voltage across a calibrated RF load which can be nominal resistive or nonnominal with parallel susceptance. They give an analysis of accuracy, including effects of RF harmonics.
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Abstract Previous studies have confirmed the possibility of using an intravascular MR imaging guidewire (MRIG) as a heating source to enhance vascular gene transfection/expression. This motivated us to develop a new intravascular system that can perform MR imaging, radiofrequncy (RF) heating, and MR temperature monitoring simultaneously in an MR scanner. To validate this concept, a series of mathematical simulations of RF power loss along a 0.032‐inch MRIG and RF energy spatial distribution were performed to determine the optimum RF heating frequency. Then, an RF generator/amplifier and a filter box were built. The possibility for simultaneous RF heating and MR thermal mapping of the system was confirmed in vitro using a phantom, and the obtained thermal mapping profile was compared with the simulated RF power distribution. Subsequently, the feasibility of simultaneous RF heating and temperature monitoring was successfully validated in vivo in the aorta of living rabbits. This MR imaging/RF heating system offers a potential tool for intravascular MR‐mediated, RF‐enhanced vascular gene therapy. Magn Reson Med 54:226–230, 2005. © 2005 Wiley‐Liss, Inc.
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Two electromagnetic heating methods have been studied in the hyperthermic treatment of cancer: dielectric heating, and induction heating using magnetic substances. Dielectric heating devices heat even normal tissues around cancer. On the other hand, induction heating has an advantage that it can heat cancer selectively. However, so far effective induction heating has been difficult: enough heat was not generated in the body because of (1) the magnetic field generated by portable induction heating devices was not strong enough, and (2) non-existence of excellent magnetic substances, and (3) strongly invasive temperature measurement in the body. In this paper, we try to solve those problems.Firstly, we develop an effective high-power induction heating device. Secondly, we obtain an excellent superparamagnetic substance known as magnetic fluid (MF) with large magnetic particles. Thirdly, we propose a detection technique of magnetic particle distribution in the body, using X-ray CT, from which the internal body temperature can be estimated. We confirm the validity of the proposed method in vitro. Finally, we do an experiment to heat the excellent MF injected into VX-2 bearing rabbits. A significant anti-cancer effect was observed. Such results suggest that our study would be quite useful for the development of induction heating hyperthermia.
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Electromagnetic induction
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An analysis technique has been developed that allows for the determination of the transistor dynamic I-V characteristics (RF l-V) directly from CW large signal RF measurements. A key feature of this technique is that it is performed under RF operation conditions similar to those found in power amplifiers under CW RF drive conditions. Investigations have shown that these dynamic RF I-V's are independent of initial DC bias conditons and RF drive level for the MODFET structures investigated in this paper. These dynamic RF I-V's can be directly compared with DC I-V's to allow for the investigation of phenomenas like dispersion, RF breakdown and thermal effects etc.. To demonstrate their potential capability in the area of non-linear modelling these RF I-V's have been used for non-linear parameter extraction of a relatively simple large signal model. A good comparison between the simulated and measured large signal behaviour even for the higher harmonics has been achieved.
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Unipolar radiofrequency (RF) is applied with a single electrode. Unipolar RF is to be distinguished from monopolar RF, which utilizes one active electrode and one return electrode. Aesthetic applications for unipolar RF are based on tissue heating. By understanding how various RF parameters, including RF frequency, power, coupling, and impedance matching, can impact the path of RF flow and its interaction with tissue, one can optimize the RF application for various indications. The current chapter examines the effect of each of these parameters on the flow of RF and on the efficiency of heating biological tissues.
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