Download or read book Radio Frequency Pulse Designs for Magnetic Resonance Imaging at High Field written by Jason E. Moore and published by . This book was released on 2011 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Rf Pulse Design for Parallel Excitation in Magnetic Resonance Imaging written by Yinan Liu and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Parallel excitation is an emerging technique to improve or accelerate multi-dimensional spatially selective excitations in magnetic resonance imaging (MRI) using multi-channel transmit arrays. The technique has potential in many applications, such as accelerating imaging speed, mitigating field inhomogeneity in high-field MRI, and alleviating the susceptibility artifact in functional MRI (fMRI). In these applications, controlling radiofrequency (RF) power deposition (quantified by Specific Absorption Rate, or SAR) under safe limit is a critical issue, particularly in high-field MRI. This \dissertation will start with a review of multidimensional spatially selective excitation in MRI and current parallel excitation techniques. Then it will present two new RF pulse design methods to achieve reduced local/global SAR for parallel excitation while preserving the time duration and excitation pattern quality. Simulations incorporating human-model based tissue density and dielectric property were performed. Results have show that the proposed methods can achieve significant SAR reductions without enlonging the pulse duration at high-fields.

Download or read book Radio frequency Coil Design for High Field Magnetic Resonance Imaging written by Gene Bogdanov and published by . This book was released on 2002 with total page 404 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Non selective Refocusing Pulse Design in Parallel Transmission for Magnetic Resonance Imaging of the Human Brain at Ultra High Field written by Aurélien Massire and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In Magnetic Resonance Imaging (MRI), the increase of the static magnetic field strength is used to provide in theory a higher signal-to-noise ratio, thereby improving the overall image quality. The purpose of ultra-high-field MRI is to achieve a spatial image resolution sufficiently high to be able to distinguish structures so fine that they are currently impossible to view in a non-invasive manner. However, at such static magnetic fields strengths, the wavelength of the electromagnetic waves sent to flip the water proton spins is of the same order of magnitude than the scanned object. Interference wave phenomena are then observed, which are caused by the radiofrequency (RF) field inhomogeneity within the object. These generate signal and/or contrast artifacts in MR images, making their exploitation difficult, if not impossible, in certain areas of the body. It is therefore crucial to provide solutions to mitigate the non-uniformity of the spins excitation. Failing this, these imaging systems with very high fields will not reach their full potential.For relevant high field clinical diagnosis, it is therefore necessary to create RF pulses homogenizing the excitation of all spins (here of the human brain), and optimized for each individual to be imaged. For this, an 8-channel parallel transmission system (pTX) was installed in our 7 Tesla scanner. While most clinical MRI systems only use a single transmission channel, the pTX extension allows to simultaneously playing various forms of RF pulses on all channels. The resulting sum of the interference must be optimized in order to reduce the non-uniformity typically seen.The objective of this thesis is to synthesize this type of tailored RF pulses, using parallel transmission. These pulses will have as an additional constraint the compliance with the international exposure limits for radiofrequency exposure, which induces a temperature rise in the tissue. In this sense, many electromagnetic and temperature simulations were carried out as an introduction of this thesis, in order to assess the relationship between the recommended RF exposure limits and the temperature rise actually predicted in tissues.This thesis focuses specifically on the design of all RF refocusing pulses used in non-selective MRI sequences based on the spin-echo. Initially, only one RF pulse was generated for a simple application: the reversal of spin dephasing in the transverse plane, as part of a classic spin echo sequence. In a second time, sequences with very long refocusing echo train applied to in vivo imaging are considered. In all cases, the mathematical operator acting on the magnetization, and not its final state as is done conventionally, is optimized. The gain in high field imaging is clearly visible, as the necessary mathematical operations (that is to say, the rotation of the spins) are performed with a much greater fidelity than with the methods of the state of the art. For this, the generation of RF pulses is combining a k-space-based spin excitation method, the kT-points, and an optimization algorithm, called Gradient Ascent Pulse Engineering (GRAPE), using optimal control.This design is relatively fast thanks to analytical calculations rather than finite difference methods. The inclusion of a large number of parameters requires the use of GPUs (Graphics Processing Units) to achieve computation times compatible with clinical examinations. This method of designing RF pulses has been experimentally validated successfully on the NeuroSpin 7 Tesla scanner, with a cohort of healthy volunteers. An imaging protocol was developed to assess the image quality improvement using these RF pulses compared to typically used non-optimized RF pulses. All methodological developments made during this thesis have contributed to improve the performance of ultra-high-field MRI in NeuroSpin, while increasing the number of MRI sequences compatible with parallel transmission.

Download or read book The Principles of Nuclear Magnetism written by A. Abragam and published by Oxford University Press. This book was released on 1961 with total page 666 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Principles of Nuclear Magnetism

Download or read book Ultra High Field Magnetic Resonance Imaging written by Pierre-Marie Robitaille and published by Springer Science & Business Media. This book was released on 2007-12-31 with total page 487 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Radiofrequency Pulses for Improved Simultaneous Multislice Magnetic Resonance Imaging written by Anuj Sharma and published by . This book was released on 2015 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Preamplifier Noise Figure Measurement and Radio Frequency Field Optimization in High Field Magnetic Resonance Imaging written by Russell Luke Lagore and published by . This book was released on 2014 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: High field magnetic resonance imaging (MRI) is an area of research interest due to the associated improvement in image quality possible. This improvement comes at a cost. Hardware design becomes more complex in order to overcome technical challenges at these higher field strengths. Signal-to-noise ratio is of paramount importance to MR image quality and this comes from carefully designed hardware and pulse sequences. This thesis focuses on the radiofrequency hardware of a high field MRI system. As frequency increases, the difficulties associated with radiofrequency hardware design increase. A noise figure and noise parameter measurement system was developed for measurement of the noise added by measurement electronics in MRI. Noise figure was found to increase for many transistor semiconductors as magnetic field increased. The radiofrequency transmit field was also studied. Radiofrequency hardware was modified to optimize the radiofrequency field to achieve proper contrast in MR images and improve transmit power efficiency.

Download or read book Contrast Enhanced Clinical Magnetic Resonance Imaging written by Val M. Runge and published by University Press of Kentucky. This book was released on 1997 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Open Field Magnetic Resonance Imaging written by D.H.W. Grönemeyer and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 670 pages. Available in PDF, EPUB and Kindle. Book excerpt: Covers issues related to the practice of both diagnostic and interventional MRI on this new type of open design MR scanner. The unique configuration and often mid-field strengths of these machines necessitates new strategies for both diagnostic and interventional procedures compared to that ofthe standard 1.5 tesla diagnostic-only MR scanners, to which the majority of the radiologic literature is addressed today. This broad, multi-authored work will appeal to radiologists, medical physicists, other physicians, and health care personnel.

Download or read book Radiofrequency Pulse Design for Use in Nuclear Magnetic Resonance Imaging and Localized Spectroscopy written by Timothy Paul Leslie Roberts and published by . This book was released on 1992 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electromagnetics in Magnetic Resonance Imaging written by Christopher M. Collins and published by Morgan & Claypool Publishers. This book was released on 2016-03-01 with total page 82 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the past few decades, Magnetic Resonance Imaging (MRI) has become an indispensable tool in modern medicine, with MRI systems now available at every major hospital in the developed world. But for all its utility and prevalence, it is much less commonly understood and less readily explained than other common medical imaging techniques. Unlike optical, ultrasonic, X-ray (including CT), and nuclear medicine-based imaging, MRI does not rely primarily on simple transmission and/or reflection of energy, and the highest achievable resolution in MRI is orders of magnitude smaller that the smallest wavelength involved. In this book, MRI will be explained with emphasis on the magnetic fields required, their generation, their concomitant electric fields, the various interactions of all these fields with the subject being imaged, and the implications of these interactions to image quality and patient safety. Classical electromagnetics will be used to describe aspects from the fundamental phenomenon of nuclear precession through signal detection and MRI safety. Simple explanations and Illustrations combined with pertinent equations are designed to help the reader rapidly gain a fundamental understanding and an appreciation of this technology as it is used today, as well as ongoing advances that will increase its value in the future. Numerous references are included to facilitate further study with an emphasis on areas most directly related to electromagnetics.

Download or read book Mathematics and Physics of Emerging Biomedical Imaging written by Committee on the Mathematics and Physics of Emerging Dynamic Biomedical Imaging and published by National Academies Press. This book was released on 1996-03-13 with total page 261 pages. Available in PDF, EPUB and Kindle. Book excerpt: This cross-disciplinary book documents the key research challenges in the mathematical sciences and physics that could enable the economical development of novel biomedical imaging devices. It is hoped that the infusion of new insights from mathematical scientists and physicists will accelerate progress in imaging. Incorporating input from dozens of biomedical researchers who described what they perceived as key open problems of imaging that are amenable to attack by mathematical scientists and physicists, this book introduces the frontiers of biomedical imaging, especially the imaging of dynamic physiological functions, to the educated nonspecialist. Ten imaging modalities are covered, from the well-established (e.g., CAT scanning, MRI) to the more speculative (e.g., electrical and magnetic source imaging). For each modality, mathematics and physics research challenges are identified and a short list of suggested reading offered. Two additional chapters offer visions of the next generation of surgical and interventional techniques and of image processing. A final chapter provides an overview of mathematical issues that cut across the various modalities.

Download or read book Ultra high Field Magnetic Resonance Imaging Mri Instrumentation And Clinical Implementation written by Shaileshkumar B. Raval, Ph.D. and published by Index of Sciences Ltd. This book was released on 2021-04-06 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt: Magnetic Resonance Imaging“Magnetic Resonance Imaging” (MRI) is the most widely clinically used diagnostic tool for soft tissue imaging. This advanced technology and its applications are under continuous research and development, ranging from lower fields to ultra-high fields to the highest possible fields for preclinical (animal) and human imaging. Formerly known as Nuclear Magnetic Resonance Imaging (NMR), with the rising demands of clinical diagnosis requirements, it is under constant development and innovation in hospitals for populations around the world because of constant desire to go to higher fields that lead to unique research and clinical applications that aren’t achievable with other commercially and or research technologies. The basics of MRIThe human body is rich in hydrogen, when a human body is subjected to a large magnetic field, many of the free hydrogen nuclei align themselves with the direction of the magnetic field. MRI works on the principle of the directional magnetic field associated with charged particles in motion. MRI is also known as nuclear magnetic resonance imaging, a technique used to create images of parts of the human body based on the resonance of nuclei in motion under the effect of a magnetic field. Overview of the bookThis book’s lucid style makes it an easy read. It is written in a simple and comprehensible way, making it easy to followand readfor a large audience ranging from students to researchers. The areas covered include an overview of the theories and practical aspects of High-Field MRIwith each chapter Introduction, Challenges, Objectives, Methods(Materials), Results, Discussion, FutureWworks,including basic concepts, along with research-oriented and clinical concepts, technologies that are researched and developed, and implemented clinically, and published nationally and internationally recognized conferences, and publications with global awards recognition from ISMRM, TTS, and many other academic and industry organizationsthat are recognized worldwide. In this book, unexplored research theories are described along with a list of products, project developments, and completion of major and unattempted theories, which are considered to be challenging in high-field MRI. These unexplored research theories are further delved into to emerge with practical and translational products, as described in various chapters. These products are deemed to be of potential research and clinical use if implemented in clinical and hospital settings, to help thus could the patients as well as healthy populations to improve the standard of their lives. Advances in extremities and musculoskeletal imaging in patients undergoing transplants, including first-ever(never been implemented)technologies such as Ultra high field upper extremity RF coils, research publications, and intellectual properties have been explored in detail. Another major advancement discussed in this book is the Whole-body MRI RF high density transmit coil and receiver array designs(first evevr application of antenna design), published in national and international journals as intellectual properties. Various other aspects of these 4intellectual properties have been discussed such as instrumentation developed, design procedures, Electromagnetic Simulations (simulated versions), Novel whole head(Brain) MRI RF array, Innovative Visualization Techniques, Neuro and vascular flow imaging, Segmentation methods. Regenerative Imaging, Pre and post-operative (surgical) imaging, clinical implementations, pulse sequence developments and optimizations, imaging resultswith 3D volume Texture and Visualizations, also peer research and references from around the world, plus future works, and more have been entailed. This is a rather different book in terms of depth and detail in which the subject is dealt with in this book. The data is well represented with tables, equations, and nearly three hundred figures. Combining technologies, research, and clinical applications of innovations in the field of MRI, it is one of a kind and a treat for curious minds. The content is mainly focused on whole head imaging, whole-body imaging, and extremity imaging, describing their clinical applications and their implementation for high risk and high demand patient populations, healthy populations for enhanced human anatomical, biological, functional and physiological performances in a detailed manner. The research has been utilized by peers in their studies, research, publications, and learning as part of the research and clinical developments, and implementations. This book presents the author’s original research works and their applications in the real world to offer advanced innovations to the healthcare sector and improve quality and standard of life for the masses around the world and beyond as future goals as there are many aviations,Biomedical Applications and projects are in demand. The author’s research works have been publishedand awarded in various nationalllyand internationallyrecognized journals and presented in numerous conferences as well. The chapters of this book are each one of the many research publications by the author

Download or read book Parallel Radiofrequency Transmission for 3 Tesla and 7 Tesla Magnetic Resonance Imaging written by Filiz Yetişir and published by . This book was released on 2017 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: Magnetic resonance imaging (MRI) is a noninvasive imaging technique with high soft tissue contrast. MR scanners are characterized by their main magnetic field strength. Commercially available clinical MR scanners commonly have main field strengths of 1.5 and 3 Tesla. Researchers increasingly explore clinical benefits of higher field strength scanners as they provide higher signal to noise ratio and higher resolution images. On the other hand, higher field strength imaging comes with increased image shading leading to non-uniform image contrast. Moreover, the tissue heating rate due to radiofrequency (RF) energy deposition (also called specific absorption rate or SAR) increases, limiting the imaging speed. Parallel RF transmission (pTx) was proposed to address both of these challenges by optimization of RF pulses transmitted from multiple independent channels simultaneously. However, both the RF pulse design and RF safety management become more complicated with pTx. In this work, a framework to apply pTx to 3T fetal and 7T brain imaging is developed to address the image shading and high SAR issues. Fetal imaging where a large pregnant torso is imaged rapidly to avoid fetal motion artifacts, suffers from similar levels of image shading and imaging limitations by SAR to 7T brain MRI. Hence the same techniques benefit both application domains. First, a SAR constrained pTx RF pulse design technique is developed for slice selective high flip angle imaging which is clinically the most common imaging technique. Next, the performance of the developed technique in reducing SAR and the image contrast non-uniformity is demonstrated through simulations and in phantom experiments for 7T brain imaging. Then, a comprehensive RF safety workflow for an 8 channel pTx system at 7T is developed. Finally, the potential of pTx for fetal imaging at 3T is demonstrated with simulation studies and a protected fetus mode of pTx was created using additional constraints in the RF pulse design. By addressing the two main RF transmission challenges associated with high and ultrahigh field MRI, this work aims to help bring the benefits of 7T brain imaging into routine clinical use and significantly improve the clinical experience for 3T fetal imaging.

Download or read book Radio Frequency Probes for Ultra high Field Magnetic Resonance Imaging written by Daniel James Lee and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes the design, construction and testing of a dome coil. The dome coil is hemispherical in shape and is intended to be used within a set of hemispherical gradient coils in a seven tesla magnetic resonance imaging magnet. The dome coil has eight independent elements and is designed to be used for parallel transmission and reception. It is shown that the dome coil produces less specific absorption rate than a conventional birdcage coil and is suitable for head imaging. A study of travelling wave magnetic resonance imaging is also presented. In this study two different methods of generating a travelling wave (using a patch antenna and an end-fire helix antenna) are compared, and the power requirements and specific absorption rate of the travelling wave approach are considered. It is concluded that travelling wave magnetic resonance imaging is best performed using a local receive coil and with the travelling wave antenna placed at least 50 cm from the subject. All theory relevant to the design, construction, testing and use of these coils and antennas is also presented.

Download or read book Design of Multidimensional Large Tip Angle Radiofrequency Pulses for Parallel Transmission in Magnetic Resonance Imaging written by and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: