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Статті в журналах з теми "Radio-Frequency (RF) coils"
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Truszkiewicz, Adrian, David Aebisher, Zuzanna Bober, Łukasz Ożóg, and Dorota Bartusik-Aebisher. "Radio Frequency MRI coils." European Journal of Clinical and Experimental Medicine 18, no. 1 (2020): 24–27. http://dx.doi.org/10.15584/ejcem.2020.1.5.
Повний текст джерелаАнотація:
Introduction. Magnetic Resonance Imaging (MRI) coils technology is a powerful improvement for clinical diagnostics. This includes opportunities for mathematical and physical research into coil design. Aim. Here we present the method applied to MRI coil array designs. Material and methods. Analysis of literature and self-research. Results. The coils that emit the radiofrequency pulses are designed similarly. As much as possible, they deliver the same strength of radiofrequency to all voxels within their imaging volume. Surface coils on the other hand are usually not embedded in cylindrical surfaces relatively close to the surface of the body. Conclusion. The presented here results relates to the art of magnetic resonance imaging (MRI) and RF coils design. It finds particular application of RF coils in conjunction with bore type MRI scanners.
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Seo, Jeung-Hoon, Yeunchul Ryu, and Jun-Young Chung. "Simulation Study of Radio Frequency Safety and the Optimal Size of a Single-Channel Surface Radio Frequency Coil for Mice at 9.4 T Magnetic Resonance Imaging." Sensors 22, no. 11 (June 3, 2022): 4274. http://dx.doi.org/10.3390/s22114274.
Повний текст джерелаАнотація:
The optimized size of a single-channel surface radio frequency (RF) coil for mouse body images in a 9.4 T magnetic resonance imaging (MRI) system was determined via electromagnetic-field analysis of the signal depth according to the size of a single-channel coil. The single-channel surface RF coils used in electromagnetic field simulations were configured to operate in transmission/reception mode at a frequency of 9.4 T–400 MHz. Computational analysis using the finite-difference time-domain method was used to assess the single-channel surface RF coil by comparing single-channel surface RF coils of varying sizes in terms of |B1|-, |B1+|-, |B1−|- and |E|-field distribution. RF safety for the prevention of burn injuries to small animals was assessed using an analysis of the specific absorption rate. A single-channel surface RF coil with a 20 mm diameter provided optimal B1-field distribution and RF safety, thus confirming that single-channel surface RF coils with ≥25 mm diameter could not provide typical B1-field distribution. A single-channel surface RF coil with a 20 mm diameter for mouse body imaging at 9.4 T MRI was recommended to preserve the characteristics of single-channel surface RF coils, and ensured that RF signals were applied correctly to the target point within RF safety guidelines.
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Seo, Jeung-Hoon, Young-Seung Jo, Chang-Hyun Oh, and Jun-Young Chung. "A New Combination of Radio-Frequency Coil Configurations Using High-Permittivity Materials and Inductively Coupled Structures for Ultrahigh-Field Magnetic Resonance Imaging." Sensors 22, no. 22 (November 19, 2022): 8968. http://dx.doi.org/10.3390/s22228968.
Повний текст джерелаАнотація:
In ultrahigh-field (UHF) magnetic resonance imaging (MRI) system, the RF power required to excite the nuclei of the target object increases. As the strength of the main magnetic field (B0 field) increases, the improvement of the RF transmit field (B1+ field) efficiency and receive field (B1− field) sensitivity of radio-frequency (RF) coils is essential to reduce their specific absorption rate and power deposition in UHF MRI. To address these problems, we previously proposed a method to simultaneously improve the B1+ field efficiency and B1− field sensitivity of 16-leg bandpass birdcage RF coils (BP-BC RF coils) by combining a multichannel wireless RF element (MCWE) and segmented cylindrical high-permittivity material (scHPM) comprising 16 elements in 7.0 T MRI. In this work, we further improved the performance of transmit/receive RF coils. A new combination of RF coil with wireless element and HPM was proposed by comparing the BP-BC RF coil with the MCWE and the scHPM proposed in the previous study and the multichannel RF coils with a birdcage RF coil-type wireless element (BCWE) and the scHPM proposed in this study. The proposed 16-ch RF coils with the BCWE and scHPM provided excellent B1+ field efficiency and B1− field sensitivity improvement.
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Ahmad, Sheikh Faisal, Young Cheol Kim, Ick Chang Choi, and Hyun Deok Kim. "Recent Progress in Birdcage RF Coil Technology for MRI System." Diagnostics 10, no. 12 (November 27, 2020): 1017. http://dx.doi.org/10.3390/diagnostics10121017.
Повний текст джерелаАнотація:
The radio frequency (RF) coil is one of the key components of the magnetic resonance imaging (MRI) system. It has a significant impact on the performance of the nuclear magnetic resonance (NMR) detection. Among numerous practical designs of RF coils for NMR imaging, the birdcage RF coil is the most popular choice from low field to ultra-high field MRI systems. In the transmission mode, it can establish a strong and homogeneous transverse magnetic field B1 for any element at its Larmor frequency. Similarly, in the reception mode, it exhibits extremely high sensitivity for the detection of even faint NMR signals from the volume of interest. Despite the sophisticated 3D structure of the birdcage coil, the developments in the design, analysis, and implementation technologies during the past decade have rendered the development of the birdcage coils quite reasonable. This article provides a detailed review of the recent progress in the birdcage RF coil technology for the MRI system.
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Duan, Yunsuo, Tamer S. Ibrahim, Bradley S. Peterson, Feng Liu, and Alayar Kangarlu. "Assessment of a PML Boundary Condition for Simulating an MRI Radio Frequency Coil." International Journal of Antennas and Propagation 2008 (2008): 1–10. http://dx.doi.org/10.1155/2008/563196.
Повний текст джерелаАнотація:
Computational methods such as the finite difference time domain (FDTD) play an important role in simulating radiofrequency (RF) coils used in magnetic resonance imaging (MRI). The choice of absorbing boundary conditions affects the final outcome of such studies. We have used FDTD to assess the Berenger's perfectly matched layer (PML) as an absorbing boundary condition for computation of the resonance patterns and electromagnetic fields of RF coils. We first experimentally constructed a high-pass birdcage head coil, measured its resonance pattern, and used it to acquire proton phantom MRI images. We then computed the resonance pattern and field of the coil using FDTD with a PML as an absorbing boundary condition. We assessed the accuracy and efficiency of PML by adjusting the parameters of the PML and comparing the calculated results with measured ones. The optimal PML parameters that produce accurate (comparable to the experimental findings) FDTD calculations are then provided for the birdcage head coil operating at 127.72 MHz, the Larmor frequency of at 3 Tesla (T).
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Aebischer, H. A. "Inductance Formula for Square Spiral Inductors with Rectangular Conductor Cross Section." Advanced Electromagnetics 8, no. 4 (September 10, 2019): 80–88. http://dx.doi.org/10.7716/aem.v8i4.1074.
Повний текст джерелаАнотація:
Planar spiral coils are used as inductors in radio frequency (RF) microelectronic integrated circuits (IC’s) and as antennas in both radio frequency identification (RFID) and telemetry systems. They must be designed to a specified inductance. From the literature, approximate analytical formulae for the inductance of such coils with rectangular conductor cross section are known. They yield the direct current (DC) inductance, which is considered as a good approximation for inductors in RF IC’s up to the GHz range. In principle, these formulae can simplify coil design considerably. But a recent comparative study of the most cited formulae revealed that their maximum relative error is often much larger than claimed by the author, and too large to be useful in circuit design.
This paper presents a more accurate formula for the DC inductance of square planar spiral coils than was known so far. It is applicable to any design of such coils with up to windings. Owing to its scalability, this holds irrespectively of the coil size and the inductance range. It lowers the maximum error over the whole domain of definition from so far down to . This has been tested by the same method used in the comparative study mentioned above, where the precise reference inductances were computed with the help of the free standard software FastHenry2. A comparison to measurements is included. Moreover, the source code of a MATLAB® function to implement the formula is given in the appendix.
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Hong, Seon-Eui, Sukhoon Oh, and Hyung-Do Choi. "RF Exposure Assessment for Various Poses of Patient Assistant in Open MRI Environment." Applied Sciences 11, no. 11 (May 28, 2021): 4967. http://dx.doi.org/10.3390/app11114967.
Повний текст джерелаАнотація:
In this study, the radio-frequency (RF) energy exposure of patient assistants was assessed for an open magnetic resonance imaging (MRI) system based on numerical computations of the head and body RF coil. Various poses of the patient assistants were defined to see how poorly they affected the RF energy exposure. For the assessments, the peak spatial-averaged specific absorption rate (SAR) levels were carefully compared with each patient assistant pose based on the finite-difference time domain calculations of RF coil models when the patient was placed in such coils in a 0.3 Tesla open MRI system. Overall, the SAR levels of the patient assistant were much lower than those of the patient. However, significantly increased SAR levels were observed under specific conditions, including a larger loop size of the patient assistants’ arms and a closer distance to the RF coils. A comparably high level of SAR to the patient’s body was also found. More careful investigations are needed to prevent the increase of SAR in patient assistants for open MRI systems at higher field strengths.
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Ramsaroop, Neetu, and Oludayo O. Olugbara. "Wireless Power Transfer Using Harvested Radio Frequency Energy with Magnetic Resonance Coupling to Charge Mobile Device Batteries." Applied Sciences 11, no. 16 (August 21, 2021): 7707. http://dx.doi.org/10.3390/app11167707.
Повний текст джерелаАнотація:
This research paper presents the design of a wireless power transfer (WPT) circuit integrated with magnetic resonance coupling (MRC) and harvested radio frequency (RF) energy to wirelessly charge the battery of a mobile device. A capacitor (100 µF, 16 V) in the RF energy harvesting circuit stored the converted power, and the accumulated voltage stored in the capacitor was 9.46 V. The foundation of the proposed WPT prototype circuit included two coils (28 AWG)—a transmitter coil, and a receiver coil. The transmitter coil was energized by the alternating current (AC), which produced a magnetic field, which in turn induced a current in the receiver coil. The harvested RF energy (9.46 V) was converted into AC, which energized the transmitter coil and generated a magnetic field. The electronics in the receiver coil then converted the AC into direct current (DC), which became usable power to charge the battery of a mobile device. The experimental setup based on mathematical modeling and simulation displayed successful charging capabilities of MRC, with the alternate power source being the harvested RF energy. Mathematical formulae were applied to calculate the amount of power generated from the prototype circuit. LTSpice simulation software was applied to demonstrate the behavior of the different components in the circuit layout for effective WPT transfer.
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Lu, Ming, Xiaoyang Zhang, Shuyang Chai, and Xinqiang Yan. "Improving Specific Absorption Rate Efficiency and Coil Robustness of Self-Decoupled Transmit/Receive Coils by Elevating Feed and Mode Conductors." Sensors 23, no. 4 (February 6, 2023): 1800. http://dx.doi.org/10.3390/s23041800.
Повний текст джерелаАнотація:
Self-decoupling technology was recently proposed for radio frequency (RF) coil array designs. Here, we propose a novel geometry to reduce the peak local specific absorption rate (SAR) and improve the robustness of the self-decoupled coil. We first demonstrate that B1 is determined by the arm conductors, while the maximum E-field and local SAR are determined by the feed conductor in a self-decoupled coil. Then, we investigate how the B1, E-field, local SAR, SAR efficiency, and coil robustness change with respect to different lift-off distances for feed and mode conductors. Next, the simulation of self-decoupled coils with optimal lift-off distances on a realistic human body is performed. Finally, self-decoupled coils with optimal lift-off distances are fabricated and tested on the workbench and MRI experiments. The peak 10 g-averaged SAR of the self-decoupled coil on the human body can be reduced by 34% by elevating the feed conductor. Less coil mismatching and less resonant frequency shift with respect to loadings were observed by elevating the mode conductor. Both the simulation and experimental results show that the coils with elevated conductors can preserve the high interelement isolation, B1+ efficiency, and SNR of the original self-decoupled coils.
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Domenick, Robert, Phillip Foreman, David M. Parish, and Donald W. Pettibone. "4882540 Magnetic resonance imaging (MRI) apparatus with quadrature radio frequency (RF) coils." Magnetic Resonance Imaging 8, no. 6 (January 1990): I. http://dx.doi.org/10.1016/0730-725x(90)90025-w.
Повний текст джерелаДисертації з теми "Radio-Frequency (RF) coils"
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MAGGIORELLI, FRANCESCA. "Design and Development of Radio Frequency Coils for Sodium Magnetic Resonance Imaging at 7 T." Doctoral thesis, Università di Siena, 2019. http://hdl.handle.net/11365/1066803.
Повний текст джерелаАнотація:
The main goal of this Thesis is the design and development of Radio-Frequency (RF) coils for sodium Magnetic Resonance Imaging (MRI) at Ultra High Field (UHF). The advantage of using UHF MR scanners is due to the possibility to achieve improved Signal-to-Noise-Ratio (SNR) and spatial resolution. These characteristics are fundamental in case of imaging with nuclei different from proton, which provide an intrinsically lower signal because of their lower in-vivo concentration and lower gyromagnetic ratio. Moreover, the overlap between sodium and proton images allows the accurate localization of regions with an anomalous sodium concentration, thanks to the anatomically more detailed proton images. For this reason, in case of imaging with non-proton nuclei, Dual-Tuned (DT) coils are preferable, since they allow the signal acquisition in a fixed spatial orientation of the subject, thus removing the need of patient’s repositioning between two consecutive acquisitions with two different RF coil resonating at the two Larmor frequencies of proton and sodium, respectively. Therefore, with a DT coil, automatically co-registered images can be obtained. The cost to pay is an increase in the design and development complexity with respect to a standard RF coil.
In this Thesis, RF coils prototypes for sodium imaging (Larmor frequency ≃ 79 MHz) have been designed and developed for two different applications: human knee and human head imaging. Concerning the knee imaging, both surface coils, suitable for the signal reception, and volume coils, suitable for the sample excitation, have been designed and developed. All surface coils for knee imaging are dual-tuned. The first DT-RF coil prototype has been developed to study and characterize the issues related to the coupling between the two resonant structures, which usually compose a DT coil. New decoupling strategies have been proposed and developed as an alternative to the standard decoupling by using trap circuits, including models based on PIN diodes and Micro-Electro-Mechanical System (MEMS) switches. The volume RF coil for the knee imaging, built to be sensitive to the sodium signal only, has been designed according to the birdcage model. It has been developed to face with potential issues related to sodium volume coil interfacing with the MR system and signal acquisition before starting the construction of DT volume coils. Concerning the head imaging, an imbricated DT-RF coil, consisting of two concentrically placed birdcages, and the related electronic interface needed to connect the coil to the MR system, have been developed. Finally, an unconventional DT volume coil model (four-ring model), consisting of two birdcage-like resonant structures arranged on the same cylindrical surface and tuned at the two frequencies of interest, has been taken into account. The four-ring model has been optimized though electromagnetic simulations, with the main purpose of increasing the magnetic field homogeneity at the proton Larmor frequency at 7 T (≃ 300 MHz), and finally compared with the imbricated model.
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Nohava, Lena. "Concepts for Wearable Technology in MR : Lightweight Flexible Radio Frequency Coils and Optical Wireless Communication Flexible multi-turn multi-gap coaxial RF coils: design concept and implementation for Magnetic Resonance Imaging at 3 and 7 Tesla Perspectives in Wireless Radio Frequency Coil Development for Magnetic Resonance Imaging." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST069.
Повний текст джерелаАнотація:
Ce projet doctoral a été réalisé au laboratoire BioMaps de l'Université Paris-Saclay et au CMPBME de l'Université Médicale de Vienne. Afin d’améliorer la valeur diagnostique de l'IRM, il est souhaitable de réduire les durées d’acquisition, d’avoir une prise en charge plus efficace des patients et une meilleure qualité des images. Dans ce but, une instrumentation portable avec un matériel optimisé permettrait de réduire le poids, d’augmenter la flexibilité et de transmettre sans fil les signaux RMN, améliorant ainsi la sensibilité, le confort, la sécurité et la facilité d'utilisation de ces dispositifs.Dans ce contexte, nous avons étudié des antennes RF souples à câbles coaxiaux basées sur le principe des résonateurs à lignes à transmission. Ces résonateurs, pouvant posséder plusieurs tours et/ou plusieurs fentes, permettent d'optimiser la taille de l’antenne RF en fonction de l'application visée. Le concept a d'abord été étudiée in silico. De nombreux prototypes ont été construits et leurs performances ont été testées sur table et en IRM à 3 et 7 T. Les antennes coaxiales ont révélé avoir des performances robustes à la déformation, ne dégradent pas le TAS et peuvent améliorer le RSB et l'efficacité de transmission lorsqu'elles sont conformées au relief de la zone imagée. En parallèle, nous avons mené une étude approfondie des technologies de transmission sans fil en IRM. Un premier prototype de communication optique sans fil pour la transmission de données de capteurs de mouvements a été réalisé et testé. Les antennes coaxiales portables que nous avons étudiées offrent une alternative intéressante aux antennes standard en raison de leur faible poids et de leur flexibilitéThis PhD thesis work was conducted at the BioMaps laboratory at the Université Paris-Saclay and the Center for Medical Physics and Biomedical Engineering (CMPBME) at the Medical University of Vienna.To improve diagnostic value in MRI, shorter acquisitions, more efficient patient handling and improved image quality are needed. Wearable technology with optimized hardware reduces weight, increases flexibility, and could be wireless, thereby improving sensitivity, comfort, safety, and usability.In this work, flexible self-resonant coaxial transmission line resonators were investigated. Coaxial coils with multiple turns and gaps enable size optimization depending on the target application. The design was first studied in silico. Numerous prototypes were constructed and their performance was tested on the bench and in 3 and 7 T MRI. Coaxial coils were shown to be robust against bending, have no SAR penalty and improve SNR and transmit efficiency when form-fitted.A review of wireless MR, associated hardware developments and data transmission technology is given.An optical wireless communication module for sensor data transmission was demonstrated experimentally.Wearable coaxial coils offer an attractive alternative to standard coils due to low weight and flexibility. With wireless motion sensors diagnostic value in e.g. breast, knee, or cardiac MRI could be increased
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Winter, Lukas. "Detailing radio frequency controlled hyperthermia and its application in ultrahigh field magnetic resonance." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://dx.doi.org/10.18452/17012.
Повний текст джерелаАнотація:
Die vorliegende Arbeit untersucht die grundsätzliche Machbarkeit, Radiofrequenzimpulse (RF) der Ultrahochfeld (UHF) Magnetresonanztomographie (MRT) (B0≥7.0T) für therapeutische Verfahren wie die RF Hyperthermie oder die lokalisierte Freigabe von Wirkstoffträgern und Markern zu nutzen. Im Rahmen der Arbeit wurde ein 8-Kanal Sened/Empfangsapplikator entwickelt, der bei einer Protonenfrequenz von 298MHz operiert. Mit diesem weltweit ersten System konnte in der Arbeit experimentell bewiesen werden, dass die entwickelte Hardware sowohl zielgerichtete lokalisierte RF Erwärmung als auch MR Bildgebung und MR Thermometrie (MRTh) realisiert. Mit den zusätzlichen Freiheitsgraden (Phase, Amplitude) eines mehrkanaligen Sendesystems konnte aufgezeigt werden, dass der Ort der thermischen Dosierung gezielt verändert bzw. festgelegt werden kann. In realitätsnahen Temperatursimulationen mit numerischen Modellen des Menschen, wird in der Arbeit aufgezeigt, dass mittels des entwickelten Hybridaufbaus eine kontrollierte und lokalisierte thermische Dosierung im Zentrum des menschlichen Kopfes erzeugt werden kann. Nach der erfolgreichen Durchführung dieser Machbarkeitsstudie wurden in theoretischen Überlegungen, numerischen Simulationen und in ersten grundlegenden experimentellen Versuchen die elektromagnetischen Gegebenheiten von MRT und lokal induzierter RF Hyperthermie für Frequenzen größer als 298MHz untersucht. In einem Frequenzbereich bis zu 1.44GHz konnte der Energiefokus mit Hilfe spezialisierter RF Antennenkonfigurationen entscheidend weiter verkleinert werden, sodass Temperaturkegeldurchmesser von wenigen Millimetern erreicht wurden. Gleichzeitig konnte gezeigt werden, dass die vorgestellten Konzepte ausreichende Signalstärke der zirkular polarisierten Spinanregungsfelder bei akzeptabler oberflächlicher Energieabsorption erzeugen, um eine potentielle Machbarkeit von in vivo MRT bei B0=33.8T oder in vivo Elektronenspinresonanz (ESR) im L-Band zu demonstrieren.The presented work details the basic feasibility of using radiofrequency (RF) fields generated by ultrahigh field (UHF) magnetic resonance (MR) (B0≥7.0T) systems for therapeutic applications such as RF hyperthermia and targeted drug delivery. A truly hybrid 8-channel transmit/receive applicator operating at the 7.0T proton MR frequency of 298MHz has been developed. Experimental verification conducted in this work demonstrated that the hybrid applicator supports targeted RF heating, MR imaging and MR thermometry (MRTh). The approach offers extra degrees of freedom (RF phase, RF amplitude) that afford deliberate changes in the location and thermal dose of targeted RF induced heating. High spatial and temporal MR temperature mapping can be achieved due to intrinsic signal-to-noise ratio (SNR) gain of UHF MR together with the enhanced parallel imaging performance inherent to the multi-channel receive architecture used. Temperature simulations in human voxel models revealed that the proposed hybrid setup is capable to deposit a controlled and localized RF induced thermal dose in the center of the human brain. After demonstrating basic feasibility, theoretical considerations and proof-of-principle experiments were conducted for RF frequencies of up to 1.44GHz to explore electrodynamic constraints for MRI and targeted RF heating applications for a frequency range larger than 298MHz. For this frequency regime a significant reduction in the effective area of energy absorption was observed when using dedicated RF antenna arrays proposed and developed in this work. Based upon this initial experience it is safe to conclude that the presented concepts generate sufficient signal strength for the circular polarized spin excitation fields with acceptable specific absorption rate (SAR) on the surface, to render in vivo MRI at B0=33.8T or in vivo electron paramagnetic resonance (EPR) at L-Band feasible.
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Cassidy, Paul Joseph. "Radio-frequency coil design for magnetic resonance imaging and spectroscopy." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249272.
Повний текст джерела
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Serano, Peter James. "Design of a Multi-Array Radio-Frequency Coil for Interventional MRI of the Female Breast." Digital WPI, 2009. https://digitalcommons.wpi.edu/etd-theses/747.
Повний текст джерелаАнотація:
A new method for the simulation of radio frequency (RF) coils has been developed. This method utilizes the FEM simulation package Ansoft HFSS as a base for the modeling of RF coils with complex biological loading effects. The abilities of this software have been augmented with custom MATLAB code to enable the fast prediction of lumped element values needed to properly tune and match the coil structure as well as to perform the necessary post processing of simulation data in order to quickly generate and evaluate field data of the resonating coil and compare design variations. This method was evaluated for accuracy and implemented in the re-design of an existing four channel breast coil array for clinical imaging of the female breasts. Based on the simulation results, a commercially viable printed circuit board (PCB) implementation was developed and tested in a clinical 1.5 T MR scanner. The new design allows for wide open bilateral access to the breast regions in order to accommodate various interventional procedures. The layout has also increased axillary B1 field coverage with minor penalty to the signal-to-noise ratio of the coil array, enabling high-resolution imaging over a wide field-of-view.
Частини книг з теми "Radio-Frequency (RF) coils"
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Lemdiasov, Rosti, Arun Venkatasubramanian, and Ranga Jegadeesan. "Estimating Electric Field and SAR in Tissue in the Proximity of RF Coils." In Brain and Human Body Modeling 2020, 293–307. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-45623-8_18.
Повний текст джерелаАнотація:
AbstractMedical implants that require recharging typically use magnetic resonant coupling of transmit (external) and receive (internal) RF coils. Apart from magnetic field, the transmit coil creates a time-varying electric field that excites currents not only in the receive coil but also in the surrounding tissues. Radio frequency (RF) exposure assessment for inductive systems used in wireless powering and telemetry is done using electric field, specific absorption rate (SAR), and induced current as metrics. Full-wave analysis using RF simulation tools such as Ansys HFSS is generally used to estimate these metrics, and the results are widely accepted. However, such simulation-based analysis is quite rigorous and time-consuming, let alone the complexities with setting up the simulation.In this paper, we present a simple approach to estimating exposure (electric field, SAR, induced current) from fundamental electromagnetic principles enabling ability to arrive at results quickly. It significantly reduces the computational time in iterative approaches where multiple simulation runs are needed.
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Noetscher, Gregory, Peter Serano, Ara Nazarian, and Sergey Makarov. "Computational Tool Comprising Visible Human Project® Based Anatomical Female CAD Model and Ansys HFSS/Mechanical® FEM Software for Temperature Rise Prediction Near an Orthopedic Femoral Nail Implant During a 1.5 T MRI Scan." In Brain and Human Body Modelling 2021, 133–51. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-15451-5_9.
Повний текст джерелаАнотація:
AbstractThis medical device development tool (MDDT) is categorized as a non-clinical assessment model (NAM). This MDDT is a computational modeling and simulation tool. It can predict heating of metallic orthopedic implants with the radio frequency (RF) electromagnetic fields in the magnetic resonance imaging (MRI) coils while targeting a mid-aged and elderly female population primarily affected by osteoporosis and the associated bone fracture.This MDDT uses a high resolution anatomical female CAD (computer aided design) model coupled with the proven multiphysics finite element method (FEM) software (Ansys Workbench) to simulate the complete MRI environment. The environment is consisting of a tuned MRI coil with the given output power, detailed heterogeneous human model within the coil at the given landmark and a properly embedded metallic implant within the anatomical model to compute the extent of heating generated around the implant.Specifically, this MDDT is the in silico analog of an MRI scan for an elderly female subject with a metallic orthopedic implant at 1.5 T in a full-body birdcage RF coil.
Тези доповідей конференцій з теми "Radio-Frequency (RF) coils"
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Chen, Xin, Sergey Vinogradov, and Adam Cobb. "Shear Horizontal Guided Wave Corrosion Detection and Quantification in Pipes via Linear Scanning Magnetostrictive Transducers (MST)." In 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/qnde2021-75249.
Повний текст джерелаАнотація:
Abstract Shear horizontal (SH) guided waves are being widely considered as a promising tool for locating wall thinning corrosion in pipelike structures. One established approach to excite such waves in pipes is through the magnetostrictive transducers (MsT), which is an electromagnetic-based guided wave transducer that offers unique advantages over other transducer types. A common practice for fast screening of defects is using an automated probe positioning system. In this paper, we report the usage of a newly designed linear scanning MsT, where an iron cobalt (FeCo) strip of a predefined length wound with radio frequency (RF) coils is attached to the testing structure using shear wave couplants and a moving permanent magnet driven by a stepper motor is used to excite SH guided waves at predefined positions. In this fashion, manual manipulation of probe is minimized which significantly increases testing speed. The performance of the linear scanning MsT at corrosion inspection is evaluated experimentally by introducing “V” shaped gradual wall thinning patches of different depths and locations on a 406 mm outer diameter (OD) steel pipe with 10 mm wall thickness. The reflection and transmission amplitudes of SH modes, as well as indications from B-scan and synthetic aperture focusing technique (SAFT) images, are extracted for corrosion detection and quantification. Numerical modeling is also conducted to facilitate the understanding of SH waves interaction with defects.
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Shrivastava, Devashish, Timothy Hanson, Robert Schlentz, William Gallagher, Carl Snyder, Lance DelaBarre, Surya Prakash, Paul Iaizzo, and J. Thomas Vaughan. "MR Safety and In Vivo Thermal Characterization of an RF Coil at 9.4T." In ASME 2007 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2007. http://dx.doi.org/10.1115/sbc2007-176078.
Повний текст джерелаАнотація:
Correlating In vivo temperatures to the radio-frequency (RF) coil induced total RF power is necessary to ensure human safety in an ultra high field magnetic resonance (MR) application. Thus to ensure human safety in an ultra high field MR head imaging experiment, temperatures were measured as a function of time in the brain and surrounding cutaneous layer of twelve human sized, anesthetized swine (mean animal weight = 52kg, SD = ±6.7kg). In vivo temperatures were correlated to the RF power by developing coil and geometry specific normalized temperatures such that the RF coil induced cranial temperature change could be obtained during an MR exam by measuring only the whole head average specific absorption rate (ASAR) and the duration of the RF deposition. Thus, the feasibility of the thermal characterization of an RF volume head coil was shown. More specifically, a continuous wave (CW) RF was deposited in porcine cranium using a four loop RF head coil at 400 MHz (proton larmor frequency at 9.4T). Temperatures were recorded continuously using an inline probe placed at a predetermined location of 15mm inside the brain and a separate probe in the cutaneous layer. To differentiate the temperature response caused by the RF from that of anesthesia, the temperatures were recorded in four unheated, anesthetized swine for the complete duration of experiments (∼8hours). To study the effect of the spatial distribution of the RF as well as the tissue thermal/electrical properties and blood perfusion, the inline temperature probe was placed at two locations (N = 4 for each location). Results showed that the thermal characterization of an RF coil was possible such that the normalized temperature maps when multiplied by the ASAR and the RF heating time would predict In vivo temperature change during heating. Further, it was shown that at 9.4 T 1) the RF heating caused an inhomogeneous normalized temperature distribution in the brain; and 2) the skin temperature change was an unreliable parameter to assess In vivo temperature change.
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Ling, J. X., Jeffrey W. Hand, and Ian R. Young. "Effect of the SAR Distribution of a Radio Frequency (RF) Coil on the Temperature Field Within a Human Leg: Numerical Studies." In ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-0570.
Повний текст джерелаАнотація:
Abstract This paper presents a three dimensional Finite Element Model for studying the effect of the specific absorption rate (SAR) distribution of a RF coil on the temperature distribution within a human leg due to the energy deposit. The model consists of fat, muscle, and bone, and has 21,158 uniform elements. The 3-D leg model was derived from the tissue maps that are obtained from the 79 sequential MR images of a volunteer’s leg. The specific absorption rate (SAR) data are from the solution to the fundamental Maxwell’s electromagnetic equations of the leg with RF coil in place using finite difference time domain (FDTD) method. The blood perfusion term, which is a function of the local tissue temperature, along with the metabolic heat as well as the SAR term, are treated as one heat source term in the classical bio-heat transfer equation. A commercial FEA code, ANSYS, was used to solve the 3-D heat conduction equation with an additional iteration method to deal with the temperature dependent source term. The 3-D temperature fields without and with the SAR term were computed, as well as the changes in temperature. They predict that the maximum temperature change occurs in approximately the same location as the maximum local SAR. The map of the temperature change clearly shows how the presence of the RF coil affect the temperature distribution within the leg. With 2 watts absorbed in the leg, about 8.8 w/kg of peak SAR value, the maximum change in temperature of the leg is about 1.74° C.
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Hawkes, Grant, John Richardson, Dirk Gombert, and John Morrison. "Heat Transfer Model for an RF Cold Crucible Induction Heated Melter." In ASME 2003 Heat Transfer Summer Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/ht2003-47397.
Повний текст джерелаАнотація:
A method to reduce radioactive waste volume that includes melting glass in a cold crucible radio frequency induction heated melter has been investigated numerically. The purpose of the study is to correlate the numerical investigation with an experimental apparatus that melts glass in the above mentioned melter. A model has been created that couples the magnetic vector potential (real and imaginary) to a transient startup of the melting process. This magnetic field is coupled to the mass, momentum, and energy equations that vary with time and position as the melt grows. The coupling occurs with the electrical conductivity of the glass as it rises above the melt temperature of the glass and heat is generated. Natural convection within the molten glass helps determine the shape of the melt as it progresses in time. An electromagnetic force is also implemented that is dependent on the electrical properties and frequency of the coil. This study shows the progression of the melt shape with time along with temperatures, power input, velocites, and magnetic vector potential. A power controller is implemented that controls the primary coil current so that the power induced in the melt does not exceed 60 kW. The coupling with the 60 kW generator occurs with the impedance of the melt as it progresses and changes with time. With a current source of 70 Amps (rms) in the primary coil and a frequency of 2.6 MHz, the time to melt the glass takes 0.8 hours for a crucible that is 10 inches in diameter and 10 inches high.
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Hawkes, Grant. "Modeling an RF Cold Crucible Induction Heated Melter With Subsidence." In ASME 2004 Heat Transfer/Fluids Engineering Summer Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/ht-fed2004-56376.
Повний текст джерелаАнотація:
A method to reduce radioactive waste volume that includes melting glass in a cold crucible radio frequency induction heated melter has been investigated numerically. The purpose of the study is to correlate the numerical investigation with an experimental apparatus that melts glass in the above mentioned melter. Unique to this model is the subsidence of the glass as it changes from a powder to molten glass and drastically changes density. A model has been created that couples the magnetic vector potential (real and imaginary) to a transient startup of the melting process. This magnetic field is coupled to the mass, momentum, and energy equations that vary with time and position as the melt grows. The coupling occurs with the electrical conductivity of the glass as it rises above the melt temperature of the glass and heat is generated. Natural convection within the molten glass helps determine the shape of the melt as it progresses in time. An electromagnetic force is also implemented that is dependent on the electrical properties and frequency of the coil. This study shows the progression of the melt shape with time along with temperatures, power input, velocities, and magnetic vector potential. Coupled to all of this is a generator that will be used for this lab sized experiment. The coupling with the 60 kW generator occurs with the impedance of the melt as it progresses and changes with time. A power controller has been implemented that controls the primary coil current depending on the power that is induced into the molten glass region.