Download or read book Design Algorithms for Parallel Transmission in Magnetic Resonance Imaging written by Kawin Setsompop and published by . This book was released on 2008 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt: The focus of this dissertation is on the algorithm design, implementation, and validation of parallel transmission technology in Magnetic Resonance Imaging (MRI). Novel algorithms are proposed which yield excellent excitation control, low RF power requirements, methods that extend to non-linear large-flip-angle excitation, as well as a new algorithm for simultaneous spectral and spatial excitation critical to quantification of low-SNR brain metabolites in MR spectroscopic imaging. For testing and validation, these methods were implemented on a newly developed parallel transmission platform on both 3 T and 7 T MRI scanners to demonstrate the ability of these methods for highfidelity B1+ mitigation, first by excitation of phantoms and then by human imaging. Further, spatially tailored RF pulses were demonstrated beyond conventional slice- or slab-selective excitation.

Download or read book Computational Methods and Optimization Strategies for Parallel Transmission in Ultra High Field MRI written by Mihir Rajendra Pendse and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Magnetic resonance imaging (MRI) is a powerful imaging modality that is widely used in medicine for both clinical and research purposes. Despite its success, there is still a demand for improved image quality in the form of higher SNR and resolution and a promising approach to achieve this is with higher static field strengths (7 Tesla and above) corresponding to the ultra high frequency (UHF) regime of the RF pulse. At these frequencies, wavelength effects and complex interactions with biological tissue become problematic leading to field inhomogeneity artifacts and tissue heating concerns quantified by the specific absorption rate (SAR). This dissertation will focus on the excitation portion of the imaging process with parallel transmission (pTx) that involves using a transmit RF coil with multiple independent transmit channels. pTx is an effective way to address the challenges of ultra high field MRI through optimization of the transmitted pulse in a patient-specific way. We introduce the Iterative Minimization Procedure with Uncompressed Local SAR Estimate (IMPULSE) which is a novel distributed optimization algorithm that has favorable scaling properties and eliminates the need for virtual observation points (VOPs) thus resulting in superior SAR performance and shorter computation time. The optimization problem is to minimize SAR over a pulse sequence consisting of multiple slice excitations while ensuring that the flip angle inhomogeneity (FAI) for each excited slice is within some user specified tolerance. IMPULSE uses the alternating direction method of mulitpliers (ADMM) to split the optimization into two subproblems, a SAR-update and a FAI-update, that are solved at each iteration until convergence. The SAR-update can be formulated as an unconstrained minimization of a piecewise quadratic function which can be solved efficiently by using a bundle method to build a piecewise linear surrogate that can easily be minimized. The computation time for the FAI-update can be reduced by exploiting parallelization and using an efficient algorithm for projection of a point onto an ellipsoid. IMPULSE achieves superior SAR performance and reduced computation time compared to a conventional approach using virtual observation points or compared to using a generic sequential quadratic programming (SQP) solver in MATLAB. Using the Duke head model consisting of over six million voxels, minimum SAR pTx pulses were designed for 120 slices within 45 seconds with an FAI tolerance of 5\% at each slice. IMPULSE combined with variable rate selective excitation (VERSE) can also be used to improve SAR performance and reduce computation time for simultaneous multislice (SMS) excitation with a pTx-SMS pulse. This method (IMPULSE-SMS) was used for the pTx-SMS task of the ISMRM RF Pulse Design competition in 2016 and resulted in a pulse that was about 20\% shorter than the second best submission and about 10 times shorter than a conventional approach (SAR-unaware pulse design without VERSE). Increasing the number of transmit channels in a coil can give more degrees of freedom to achieve flip angle uniformity and reduce SAR but also increases cost and complexity of the hardware. Studying the performance of massively parallel transmit arrays in simulation can help determine whether investment in these arrays is justified based on new applications that are enabled. An 84 channel loop array for 10.5T with 6 rows and 14 columns was simulated using the Ella body model and applied to two novel applications: power independent of number of slices (PINS) pulses combined with pTx for SMS excitation and SAR focusing for therapeutic hyperthermia. Using this coil in addition to an insertable head gradient (slew rate of 1500 T/m/s), a pulse duration of about 13ms for a 16 slice coronal excitation with 0.4mm slice thickness with 10\% FAI was achieved. SAR focusing is possible for a range of locations throughout the head (although focusing is better at the periphery than at the center). A solution to a simplified bioheat equation indicates that achievable temperature rise would be within acceptable range for some forms of hyperthermia (but not high enough to achieve for ablation). A significant concern in SAR-aware pTx is mismatch between the patient and the tissue model used for SAR estimation since running the optimization on a mismatched model can result in significantly higher SAR compared to a perfect match. One technique to introduce robustness to this mismatch is to use the SAR terms for voxels of multiple tissue models (rather than a single model) in the cost function of IMPULSE. Results indicate that using multiple poorly matched models can achieve similar SAR performance compared to using a single closely matched model indicating that the multiple model approach is a way to get by with a sparse model library that doesn't fully represent the entire human population. A more sophisticated approach is to use deep learning to predict the 3D SAR maps from measured magnetic field maps. An initial implementation of this concept shows promise but is still inconclusive.

Download or read book Magnetic Resonance Spectroscopic Imaging Using Parallel Transmission at 7T written by Borjan Aleksandar Gagoski and published by . This book was released on 2011 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: Conventional magnetic resonance spectroscopic imaging (MRSI), also known as phase-encoded (PE) chemical shift imaging (CSI), suffers from both low signal-to-noise ratio (SNR) of the brain metabolites, as well as inflexible tradeoffs between acquisition time and spatial resolution. In addition, although CSI at higher main field strengths, e.g. 7 Tesla (T), offers improved SNR over clinical 1.5T or 3. OT scanners, the realization of these benefits is limited by severe inhomogeneities of the radio frequency (RF) excitation magnetic field (B, +), which is responsible for significant signal variation within the volume of interest (VOI) resulting in spatially dependent SNR losses. The work presented in this dissertation aims to provide the necessary means for using spectroscopic imaging for reliable and robust whole brain metabolite detection and quantification at high main field strengths. It addresses the challenges mentioned above by improving both the excitation and the readout components of the CSI acquisition. The long acquisition times of the PE CSI are significantly shortened (at least 20 fold) by implementing the time-efficient spiral CSI algorithm, while the B1 non-uniformities are corrected for using RF pulses designed for new RF excitation hardware at 7T, so-called parallel transmission (pTx). The B1 homogeneity of the pTx excitations improved at least by a factor of 4 (measured by the normalized spatial standard deviations) compared to conventional single channel transmit systems. The first contribution of this thesis describes the implementation of spiral CSI algorithm for online gradient waveform design and spectroscopic image reconstruction with standard clinical excitation protocols and applied in studies of Late-Onset Tay- Sachs (LOTS), adrenoleukodystrophy (ALD) and brain tumors. A major contribution of this thesis is pTx excitation design for CSI to provide spectral-spatial mitigation of the B1+ inhomogeneities at 7T. Novel pTx RF designs are proposed and demonstrated to yield excellent flip angle mitigation of the brain metabolites, and also enable improved suppression of the undesired water and lipid signals. A major obstacle to the deployment of 7T pTx applications for clinical imaging is the monitoring and management of local specific absorption rate (SAR). This thesis also proposes a pTx SAR monitoring system with real-time RF monitoring and shut-off capabilities.

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 Universal Parallel Transmission Pulse Design for the Human Brain and Spinal Cord MRI at 9 4T written by Ole Geldschläger and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Magnetic resonance imaging is a powerful, non-invasive technology to acquire anatomical images from the human body. Operating at a magnetic field strength of 7T or higher (i.e. ultrahigh field (UHF)) provides a higher signal-to-noise ratio, facilitates higher spatial resolutions, and potentially improves diagnostic sensitivity and specificity compared to clinical field strength, such as 1.5T or 3T. Unfortunately, UHF is accompanied with technical hurdles, from which the most problematic is the inhomogeneity in the radiofrequency transmit field. That can lead to spatially varying flip angles and, thus, to signal dropouts, local brightening or spatially altering imaging contrast. The most flexible approach to address this issue is the parallel transmission (pTx) technique, which itself has the disadvantage of a lengthy calibration procedure. To overcome the calibration procedure the 'universal pTx pulse' (UP) concept was introduced. It is a radiofrequency pulse design concept that relies on a pre-collected design database. The resulting pulses then work on a wide cohort of subjects without recalibration. As a first step, in this PhD project the advantages of imaging the human spinal cord at UHF were exploited. It was possible to acquire the first images from the human spinal cord at an ultrahigh in-plane resolution of 0.15x0.15mm2 at 9.4T. The images showed the tiny structures of the spinal cord in great detail. The signal-to-noise ratio and T2 *- times in the human spinal cord at 9.4T were presented. Furthermore, in this thesis the UP concept was further developed, in order to use UHF and the pTx technique more widely. While UPs were originally introduced for whole-brain or slice selective excitation, in this work a feasibility study for UPs for local excitation in the human brain (i.e. exciting only specific regions of the brain, while others should experience no excitation) was performed. UPs that locally excite the visual cortex area were calculated. The underlying transmit k-space trajectory for these radiofrequency pulses were 'spiral' trajectories. These local excitation UPs were successfully tested in vivo on nondatabase subjects at 9.4T. In a next step, the UP performance was further improved by optimizing the underlying transmit k-space trajectory to match the excitation target. The trajectory optimization and the UP design algorithms have been implemented into an open source software package (called OTUP) and demonstrated using simulations and in vivo experiments at 9.4T. The code was tested for three different target excitation pattern with varying complexity.

Download or read book Parallel Imaging in Clinical MR Applications written by Stefan O. Schönberg and published by Springer Science & Business Media. This book was released on 2007-01-11 with total page 548 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the first in-depth introduction to parallel imaging techniques and, in particular, to the application of parallel imaging in clinical MRI. It will provide readers with a broader understanding of the fundamental principles of parallel imaging and of the advantages and disadvantages of specific MR protocols in clinical applications in all parts of the body at 1.5 and 3 Tesla.

Download or read book PET and SPECT in Neurology written by Rudi A. J. O. Dierckx and published by Springer Nature. This book was released on 2020-10-20 with total page 1270 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive overview of the use of PET and SPECT in not only classic neurodegenerative disorders but also cerebrovascular disorders, brain tumors, epilepsy, head trauma, coma, sleeping disorders, and inflammatory and infectious diseases of the CNS. The new edition has been revised and updated to reflect recent advances and includes additional chapters, for example on the use of artificial intelligence and machine learning in imaging data analysis, the study of brain connectivity using PET and SPECT images, and the role of PET imaging in modulation of brain functioning by deep brain stimulation. The authors are renowned experts whose dedication to the investigation of neurological disorders through nuclear medicine technology has achieved international recognition. Most chapters are written jointly by a clinical neurologist and a nuclear medicine specialist to ensure a multidisciplinary approach. This state of the art compendium will be invaluable for neurologists and radiologists/nuclear medicine specialists and will also be informative for interested general practitioners and geriatricians. Companion volumes on PET and SPECT in psychiatry and in neurobiological systems complete a trilogy.

Download or read book Ultra High Field Neuro MRI written by Karin Markenroth Bloch and published by Elsevier. This book was released on 2023-08-21 with total page 628 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ultra-High Field Neuro MRI is a comprehensive reference and educational resource on the current state of neuroimaging at ultra-high field (UHF), with an emphasis on 7T. Sections cover the MR physics aspects of UHF, including the technical challenges and practical solutions that have enabled the rapid growth of 7T MRI. Individual chapters are dedicated to the different techniques that most strongly benefit from UHF, as well as chapters with a focus on different application areas in anatomical, functional and metabolic imaging. Finally, several chapters highlight the neurological and psychiatric applications for which 7T has shown benefits. The book is aimed at scientists who develop MR technologies and support clinical and neuroscience research, as well as users who want to benefit from UHF neuro MR techniques in their work. It also provides a comprehensive introduction to the field. Presents the opportunities and technical challenges presented by MRI at ultra-high field Describes advanced ultra-high field neuro MR techniques for clinical and neuroscience applications Enables the reader to critically assess the specific UHF advantages over currently available techniques at clinical field strengths

Download or read book Issues in Medical Lasers Imaging and Devices Research and Application 2013 Edition written by and published by ScholarlyEditions. This book was released on 2013-05-01 with total page 567 pages. Available in PDF, EPUB and Kindle. Book excerpt: Issues in Medical Lasers, Imaging, and Devices Research and Application: 2013 Edition is a ScholarlyEditions™ book that delivers timely, authoritative, and comprehensive information about Medical Ultrasonography. The editors have built Issues in Medical Lasers, Imaging, and Devices Research and Application: 2013 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about Medical Ultrasonography in this book to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Issues in Medical Lasers, Imaging, and Devices Research and Application: 2013 Edition has been produced by the world’s leading scientists, engineers, analysts, research institutions, and companies. All of the content is from peer-reviewed sources, and all of it is written, assembled, and edited by the editors at ScholarlyEditions™ and available exclusively from us. You now have a source you can cite with authority, confidence, and credibility. More information is available at http://www.ScholarlyEditions.com/.

Download or read book Algorithms and Architectures for Parallel Processing written by Yang Xiang and published by Springer. This book was released on 2012-09-04 with total page 581 pages. Available in PDF, EPUB and Kindle. Book excerpt: The two volume set LNCS 7439 and 7440 comprises the proceedings of the 12th International Conference on Algorithms and Architectures for Parallel Processing, ICA3PP 2012, as well as some workshop papers of the CDCN 2012 workshop which was held in conjunction with this conference. The 40 regular paper and 26 short papers included in these proceedings were carefully reviewed and selected from 156 submissions. The CDCN workshop attracted a total of 19 original submissions, 8 of which are included in part II of these proceedings. The papers cover many dimensions of parallel algorithms and architectures, encompassing fundamental theoretical approaches, practical experimental results, and commercial components and systems.

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 Innovations in MR Hardware from Ultra Low to Ultra High Field written by Elmar Laistler and published by Frontiers Media SA. This book was released on 2022-10-20 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Cardiovascular Magnetic Resonance written by Warren J. Manning and published by Elsevier Health Sciences. This book was released on 2018-04-26 with total page 672 pages. Available in PDF, EPUB and Kindle. Book excerpt: Provides state-of-the-art coverage of CMR technologies and guidelines, including basic principles, imaging techniques, ischemic heart disease, right ventricular and congenital heart disease, vascular and pericardium conditions, and functional cardiovascular disease. Includes new chapters on non-cardiac pathology, pacemaker safety, economics of CMR, and guidelines as well as new coverage of myocarditis and its diagnosis and assessment of prognosis by cardiovascular magnetic resonance, and the use of PET/CMR imaging of the heart, especially in sarcoidosis. Features more than 1,100 high-quality images representing today’s CMR imaging. Covers T1, T2 and ECV mapping, as well as T2* imaging in iron overload, which has been shown to save lives in patients with thalassaemia major Discusses the cost-effectiveness of CMR.

Download or read book Magnetic Resonance Microscopy written by Sabina Haber-Pohlmeier and published by John Wiley & Sons. This book was released on 2022-04-20 with total page 468 pages. Available in PDF, EPUB and Kindle. Book excerpt: Magnetic Resonance Microscopy Explore the interdisciplinary applications of magnetic resonance microscopy in this one-of-a-kind resource In Magnetic Resonance Microscopy: Instrumentation and Applications in Engineering, Life Science and Energy Research, a team of distinguished researchers delivers a comprehensive exploration of the use of magnetic resonance microscopy (MRM) and similar techniques in an interdisciplinary milieux. Opening with a section on hardware and methodology, the book moves on to consider developments in the field of mobile nuclear magnetic resonance. Essential processes, including filtration, multi-phase flow and transport, and a wide range of systems – from biomarkers via single cells to plants and biofilms – are discussed next. After a fulsome treatment of MRM in the field of energy research, the editors conclude the book with a chapter extoling the virtues of a holistic treatment of theory and application in MRM. Magnetic Resonance Microscopy: Instrumentation and Applications in Engineering, Life Science and Energy Research also includes: A thorough introduction to recent developments in magnetic resonance microscopy hardware and methods, including ceramic coils for MR microscopy Comprehensive explorations of applications in chemical engineering, including ultra-fast MR techniques to image multi-phase flow in pipes and reactors Practical discussions of applications in the life sciences, including MRI of single cells labelled with super paramagnetic iron oxide nanoparticles In-depth examinations of new applications in energy research, including spectroscopic imaging of devices for electrochemical storage Perfect for practicing scientists from all fields, Magnetic Resonance Microscopy: Instrumentation and Applications in Engineering, Life Science and Energy Research is an ideal resource for anyone seeking a one-stop guide to magnetic resonance microscopy for engineers, life scientists, and energy researchers.

Download or read book High Performance Computing Systems and Applications written by Robert D. Kent and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 337 pages. Available in PDF, EPUB and Kindle. Book excerpt: High Performance Computing Systems and Applications contains fully refereed papers from the 15th Annual Symposium on High Performance Computing. These papers cover both fundamental and applied topics in HPC: parallel algorithms, distributed systems and architectures, distributed memory and performance, high level applications, tools and solvers, numerical methods and simulation, advanced computing systems, and the emerging area of computational grids. High Performance Computing Systems and Applications is suitable as a secondary text for graduate level courses, and as a reference for researchers and practitioners in industry.

Download or read book An Introduction to Variational Autoencoders written by Diederik P. Kingma and published by . This book was released on 2019-11-12 with total page 102 pages. Available in PDF, EPUB and Kindle. Book excerpt: An Introduction to Variational Autoencoders provides a quick summary for the of a topic that has become an important tool in modern-day deep learning techniques.

Download or read book Proceedings of the 1995 International Conference on Parallel Processing written by Kyle Gallivan and published by CRC Press. This book was released on 1995-08-08 with total page 262 pages. Available in PDF, EPUB and Kindle. Book excerpt: This set of technical books contains all the information presented at the 1995 International Conference on Parallel Processing. This conference, held August 14 - 18, featured over 100 lectures from more than 300 contributors, and included three panel sessions and three keynote addresses. The international authorship includes experts from around the globe, from Texas to Tokyo, from Leiden to London. Compiled by faculty at the University of Illinois and sponsored by Penn State University, these Proceedings are a comprehensive look at all that's new in the field of parallel processing.