Author: Christof Thalhammer
Publisher:
ISBN:
Category :
Languages : en
Pages : 120

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Author: BuSik Park
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Radiofrequency magnetic (B1) field inhomogeneity and absorbed power in sample and RF coil have been among the main causes for image degradation in magnetic resonance imaging (MRI) since its inception. The problem becomes more pronounced at high frequencies as wavelengths in tissue become shorter. To address these problems, we present methods for design, implementation, and evaluation of RF coils considering excitation uniformity and/or specific absorption rate (SAR) for high field nuclear magnetic resonance (NMR) and MRI. Specifically, we present 1) the design of a novel radiofrequency (RF) coil for imaging of histological slices of tissue using a 7.0 T MRI system, 2) numerical model of a dielectric resonator for high field MRI, 3) a method to separate conservative and magnetically-induced electric fields from numerical calculations for MR microscopy, 4) a simple method to decrease sample heating using conductive wires, 5) a numerical analysis of conservative and magnetically-induced electric field for low-frequency human imaging, 6) numerical calculation results for the B1 field and SAR evaluation in a 3T neonate head coil, and 7) design of a slice-selective array-optimized composite pulse to improve B1 uniformity and reduce SAR using an 8-channel transmit head array loaded with a head model. The methods and results presented here can provide very useful information for designing RF coils considering excitation uniformity and SAR simultaneously in high field MRI/NMR.

Author: Bing Wu
Publisher: Open Dissertation Press
ISBN: 9781361469507
Category :
Languages : en
Pages :

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This dissertation, "Microstrip Radio-frequency Coil and Array Design for Magnetic Resonance Imaging" by Bing, Wu, 吳冰, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Microstrip Radio-frequency Coil and Array Design for Magnetic Resonance Imaging submitted by Wu Bing For the degree of Doctor of Philosophy at The University of Hong Kong in September 2006 In the past five years, microstrip RF coils have been developed and widely applied for MR applications at high magnetic fields. In contrast to conventional surface coils, the microstrip coil uses the microstrip transmission line which in its simplest form consists of a thin strip conductor and a ground plane separated by a low-loss dielectric substrate. The semi-open, unbalanced structure microstrip generates a unique B field distribution mainly on one side of the coil where a sample is located. This results in several unique features: reduced losses, higher Q- factor, reduced coupling among multiple microstrip coils. In addition, the microstrip RF coil's unbalanced nature obviates the need of a matching balun. This dissertation presents the author's investigates in microstrip RF coil and array designs at the fields higher than 1.5 Tesla. Firstly, a novel tunable loop microstrip (TLM) RF coil based on the ring resonant circuit has been presented. SNR comparison between the TLM coil and conventional surface coil has been performed at various magnetic field strengths from 1.5 Tesla to 11.1 Tesla. Our study has demonstrated that utilization of the TLM coil can substantially reduce radiation loss and deliver better SNR performance than a conventional coil at ultra high fields. Results also indicate a trend to superior performance of the TLM coil as the field increases. Secondly, several current decoupling techniques have been utilized to the TLM planar array, which consists of two identical TLM coils elements. Simulation, bench test and MRI experiments have been carried out to provide a quantitative analysis of those decoupling schemes. Thirdly, the commonly used capacitive decoupling method for microstrip arrays has been analyzed. It appears that the decoupling capacitance is usually quite small at ultra-high fields and difficult to finely tune. A capacitively decoupled TLM array has been proposed, fabricated and tested at 7 Tesla. Using the TLM array, the capacitive decoupling method can be easily applied with reasonable decoupling capacitance. Bench test and MRI experiments at 7 Tesla show that excellent isolations (-37 dB) between the adjacent elements can be achieved and this TLM array is appropriate for SENSE imaging. Lastly, a new inductive decoupling approach for microstrip arrays has been presented at fields higher than 7 Tesla. In contrast to the capacitive decoupling methods, the decoupling inductance is independent of the resonant frequency, making this method much easier to be implemented. An inductively decoupled eight- channel microstrip array has been implemented and tested at 9.4 Tesla. This decoupling approach should enable more elements to be packed into microstrip arrays for the purpose of parallel imaging at ultrahigh fields. Number of words: 425 Signature: DOI: 10.5353/th_b3704672 Subjects: Magnetic resonance imaging

Author: Pierre-Marie Robitaille
Publisher: Springer Science & Business Media
ISBN: 0387496483
Category : Medical
Languages : en
Pages : 487

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The foundation for understanding the function and dynamics of biological systems is not only knowledge of their structure, but the new methodologies and applications used to determine that structure. This volume in Biological Magnetic Resonance emphasizes the methods that involve Ultra High Field Magnetic Resonance Imaging. It will interest researchers working in the field of imaging.

Author: Gene Bogdanov
Publisher:
ISBN:
Category : Magnetic resonance imaging
Languages : en
Pages : 404

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Author: Joel Mispelter
Publisher: World Scientific Publishing Company
ISBN: 1783268042
Category : Technology & Engineering
Languages : en
Pages : 754

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Book Description
NMR Probeheads for Biophysical and Biomedical Experiments 2nd Edition is essential reading for anyone in the field of NMR or MRI, from students to medical or biological scientists performing experiments under certain physical and/or geometrical conditions, unattainable by conventional or available probes. The material guides the reader through the most basic and comprehensive stages in accomplishing a correct probe design, from a very basic oscillating circuit to much more elaborate designs.This new edition has been revised and updated to include a chapter dedicated to RF components, which are commonly used for probes realization and their frequency-dependent characteristics. Another completely revised chapter concerns the multiple coil systems and discusses arrays coils, different decoupling methods, and some principles for interfacing coils with low-noise preamplifiers. The principles of linear circuit analysis are presented in a dedicated chapter. Last but not least, accompanying files containing updated software for probe design have been made available from the publisher's website.

Author: Xiaoqun Liu
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
The increasing demands for improving magnetic resonance imaging (MRI) quality, especially reducing the imaging time have been driving the channel number of parallel magnetic resonance imaging (Parallel MRI) to increase. When the channel number increases to 64 or even 128, the traditional method of stacking the same number of radio-frequency (RF) receivers with very low level of integration becomes expensive and cumbersome. However, the cost, size, power consumption of the Parallel MRI receivers can be dramatically reduced by designing a whole receiver front-end even multiple receiver front-ends on a single chip using CMOS technology, and multiplexing the output signal of each receiver front-end into one channel so that as much hardware resource can be shared by as many channels as possible, especially the digitizer. The main object of this research is focused on the analysis and design of fully integrated multi-channel RF receiver and multiplexing technology. First, different architectures of RF receiver and different multiplexing method are analyzed. After comparing the advantages and the disadvantages of these architectures, an architecture of receiver front-end which is most suitable for fully on-chip multi-channel design is proposed and a multiplexing method is selected. According to this proposed architecture, a four-channel receiver front-end was designed and fabricated using TSMC 0.18Bm technology on a single chip and methods of testing in the MRI system using parallel planar coil array and phase coil array respectively as target coils were presented. Each channel of the receiver front-end includes an ultra low noise amplifier (LNA), a quadrature image rejection down-converter, a buffer, and a low-pass filter (LPF) which also acts as a variable gain amplifier (VGA). The quadrature image rejection downconverter consists of a quadrature generator, a passive mixer with a transimpedance amplifier which converts the output current signal of the passive mixer into voltage signal while acts as a LPF, and a polyphase filter after the TIA. The receiver has an over NF of 0.935dB, variable gain from about 80dB to 90dB, power consumption of 30.8mW, and chip area of 6mm2. Next, a prototype of 4-channel RF receiver with Time Domain Multiplexing (TDM) on a single printed circuit board (PCB) was designed and bench-tested. Then Parallel MRI experiment was carried out and images were acquired using this prototype. The testing results verify the proposed concepts.

Author: Stewart C. Bushong
Publisher: Elsevier Health Sciences
ISBN: 0323014852
Category : Medical
Languages : en
Pages : 526

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Book Description
Dette er en grundlæggende lærebog om konventionel MRI samt billedteknik. Den begynder med et overblik over elektricitet og magnetisme, herefter gives en dybtgående forklaring på hvordan MRI fungerer og her diskuteres de seneste metoder i radiografisk billedtagning, patientsikkerhed m.v.

Author: Donald W. McRobbie
Publisher: John Wiley & Sons
ISBN: 1119557178
Category : Medical
Languages : en
Pages : 405

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Book Description
Essentials of MRI Safety is a comprehensive guide that enables practitioners to recognise and assess safety risks and follow appropriate and effective safety procedures in clinical practice. The text covers all the vital aspects of clinical MRI safety, including the bio-effects of MRI, magnet safety, occupational exposure, scanning passive and active implants, MRI suite design, institutional governance, and more. Complex equations and models are stripped back to present the foundations of theory and physics necessary to understand each topic, from the basic laws of magnetism to fringe field spatial gradient maps of common MRI scanners. Written by an internationally recognised MRI author, educator, and MRI safety expert, this important textbook: Reflects the most current research, guidelines, and MRI safety information Explains procedures for scanning pregnant women, managing MRI noise exposure, and handling emergency situations Prepares candidates for the American Board of MR Safety exam and other professional certifications Aligns with MRI safety roles such as MR Medical Director (MRMD), MR Safety Officer (MRSO) and MR Safety Expert (MRSE) Contains numerous illustrations, figures, self-assessment tests, key references, and extensive appendices Essentials of MRI Safety is an indispensable text for all radiographers and radiologists, as well as physicists, engineers, and researchers with an interest in MRI.

Author: Won-Je Lee
Publisher:
ISBN:
Category :
Languages : en
Pages : 130

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