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Magnetic resonance imaging (MRI) is a powerful medical imaging modality providing excellent soft-tissue contrast without exposing the patient to ionizing radiation. In particular, MRI plays a critical role in the diagnosis and management of cardiovascular disease with the possibility of obtaining a wide range of anatomical and functional information in a single examination. However, despite technical advancements such as parallel imaging and compressed sensing, the scan time of cardiovascular MRI is still relatively long compared to X-ray or CT. The temporal resolution for functional assessment is limited, and compensation for respiratory and cardiac motion remains challenging. To improve the temporal resolution, an undersampling acquisition scheme and a low-rank matrix-completion reconstruction method recovering the missing data are developed and applied to perfusion imaging in the lower extremities. To exploit the spatial-temporal information redundancy, the proposed method formulates the image construction as an optimization problem with the low-rank constraint and the data-consistency constraint. With the proposed method, dynamic contrast-enhanced perfusion imaging in the lower extremities with high temporal resolution (3 s) and volumetric coverage ( 32x16x32 cm3) is achieved. Pulse sequence design is another approach to achieve scan acceleration. Recognizing that the region of interest (ROI) is smaller than the full spatial extent of the anatomy in coronary magnetic resonance angiography (MRA), a new magnetization preparation sequence that combines outer volume suppression with T2 preparation is designed and implemented, enabling accelerated free-breathing whole-heart coronary MRA with enhanced blood-myocardium contrast in a scan time of less than 3 minutes by reducing the image field-of-view. Two nonrigid motion-correction methods are also developed to reduce the motion artifacts generated during the scan. These two methods extract several motion trajectories from 3D image-based navigators (iNAVs) and compensate for them with an autofocusing algorithm. A bank of motion-corrected images is generated by motion correction with every motion trajectory, and the final image is assembled on a pixel-by-pixel basis with the best-focused pixel chosen from the bank of images according to a localized gradient entropy metric. The first method is developed for free-breathing whole-heart coronary MRA in which the motion is complicated and nonrigid. Both global rigid motion and localized nonrigid motion are extracted from the 3D iNAVs. The second method is designed for abdominal MRA, in which the imaging volume is divided into ROIs with different 3D translational motion patterns. An automatic ROI-clustering method is developed and a translational motion trajectory is estimated for every ROI. Both motion correction methods demonstrate improved vessel sharpness in the in vivo studies. The image reconstruction method, pulse sequence and motion-correction methods developed enable scan acceleration and motion correction to address several challenges in cardiovascular MRI. These methods show promise of extending the diagnostic utility of MRI in this application.
Motion Correction in MR: Correction of Position, Motion, and Dynamic Changes, Volume Eight provides a comprehensive survey of the state-of-the-art in motion detection and correction in magnetic resonance imaging and magnetic resonance spectroscopy. The book describes the problem of correctly and consistently identifying and positioning the organ of interest and tracking it throughout the scan. The basic principles of how image artefacts arise because of position changes during scanning are described, along with retrospective and prospective techniques for eliminating these artefacts, including classical approaches and methods using machine learning. Internal navigator-based approaches as well as external systems for estimating motion are also presented, along with practical applications in each organ system and each MR modality covered. This book provides a technical basis for physicists and engineers to develop motion correction methods, giving guidance to technologists and radiologists for incorporating these methods in patient examinations. - Provides approaches for correcting scans prospectively and retrospectively - Shows how motion and secondary effects such as field changes manifest in MR scans as artifacts and subtle biases in quantitative research - Gives methods for measuring motion and associated field changes, quantifying motion and judging the accuracy of the motion and field estimates
Magnetic resonance imaging (MRI) is a powerful medical imaging modality that offers excellent soft-tissue contrast and numerous contrast-generation mechanisms. However, due to the relatively low signal-to-noise ratio (SNR) of MRI, many volumetric and high-resolution imaging techniques require long acquisition times yielding an increased sensitivity to motion. In many cardiac MRI applications, one of the most significant challenges is the reduction of motion artifacts caused by cardiac and respiratory motion. In these applications, a combination of SNR-efficient balanced steady-state free precession (bSSFP) pulse sequences, high-temporal-resolution motion tracking acquisitions, and retrospective motion correction algorithms are commonly employed to mitigate motion artifacts. Despite recent advances in steady-state pulse sequence development, navigator motion tracking acquisitions, and motion correction algorithms, motion artifact reduction continues to be a significant challenge for many cardiac MRI applications. A novel class of perturbed steady-state free precession (SSFP) pulse sequences is developed and analyzed, yielding new forms of steady-state image contrast. These sequences utilize alternating perturbations of sequence parameters such as the repetition time (TR) and flip angle to produce oscillating steady-state frequency responses. Large oscillations of the signal magnitude and phase occur at specific off-resonant frequencies, and the combination of these signals can yield spectrally selective image contrast. Applications are demonstrated for retrospective motion correction using cardiac fat navigator acquisitions in free-breathing whole-heart cardiac MRI and for positive-contrast imaging of superparamagnetic iron-oxide nanoparticles. The bSSFP pulse sequence is widely used in cardiac imaging due to its high signal per unit time and excellent blood-myocardial contrast. A drawback of this pulse sequence is the generation of bright signal from fat, which can lead to unwanted image artifacts. Alternating repetition time (ATR) SSFP is a recently developed sequence that generates fat-suppressed steady-state contrast, but it requires the addition of an unused time interval every repetition, making it less time efficient than bSSFP. A small modification to the ATR pulse sequence is proposed to enable the acquisition of a one-dimensional self-gating signal during this unused time interval. The self-gating signals are used for retrospective cardiac triggering in breath-held cardiac cine imaging, and the proposed sequence is evaluated in volunteer and patient populations. The resulting ECG-free self-gated images have no statistically significant differences compared with conventional ECG-gated images. The proposed sequence also yields robust suppression of epicardial fat compared with standard bSSFP cardiac cine imaging. In coronary MR angiography (CMRA), high-resolution, whole-heart acquisitions are typically required for visualization of the relatively small coronary vasculature. These acquisitions require long scan times that are carried out during free breathing, which can lead to severe ghosting and blurring artifacts without motion compensation. A nonrigid retrospective motion correction technique is proposed for motion artifact reduction in image-navigated CMRA. The technique reconstructs a bank of motion-compensated CMRA images using many candidate motion estimates derived from navigator images acquired throughout the scan. A metric-based autofocusing approach is used to automatically generate a final nonrigid-motion-corrected image from this bank of images. The proposed technique is evaluated in volunteer and patient studies, leading to improvements in vessel sharpness and image quality compared with rigid-body translational motion correction. These new steady-state pulse sequences, motion tracking acquisitions, and nonrigid reconstruction techniques address several of the challenges to cardiac MRI, enabling the reduction of motion artifacts and improvement of image quality.
Magnetic Resonance Image Reconstruction: Theory, Methods and Applications presents the fundamental concepts of MR image reconstruction, including its formulation as an inverse problem, as well as the most common models and optimization methods for reconstructing MR images. The book discusses approaches for specific applications such as non-Cartesian imaging, under sampled reconstruction, motion correction, dynamic imaging and quantitative MRI. This unique resource is suitable for physicists, engineers, technologists and clinicians with an interest in medical image reconstruction and MRI. - Explains the underlying principles of MRI reconstruction, along with the latest research - Gives example codes for some of the methods presented - Includes updates on the latest developments, including compressed sensing, tensor-based reconstruction and machine learning based reconstruction
Based on research and clinical trials, this book details the latest research in magnetic resonance imaging (MRI) tagging technology related to heart mechanics. It covers clinical applications and examines future trends, providing a guide for future uses of MRI technology for studying heart mechanics.
The significantly updated second edition of this important work provides an up-to-date and comprehensive overview of cardiovascular magnetic resonance imaging (CMR), a rapidly evolving tool for diagnosis and intervention of cardiovascular disease. New and updated chapters focus on recent applications of CMR such as electrophysiological ablative treatment of arrhythmias, targeted molecular MRI, and T1 mapping methods. The book presents a state-of-the-art compilation of expert contributions to the field, each examining normal and pathologic anatomy of the cardiovascular system as assessed by magnetic resonance imaging. Functional techniques such as myocardial perfusion imaging and assessment of flow velocity are emphasized, along with the exciting areas of artherosclerosis plaque imaging and targeted MRI. This cutting-edge volume represents a multi-disciplinary approach to the field, with contributions from experts in cardiology, radiology, physics, engineering, physiology and biochemistry, and offers new directions in noninvasive imaging. The Second Edition of Cardiovascular Magnetic Resonance Imaging is an essential resource for cardiologists and radiologists striving to lead the way into the future of this important field.
Magnetic Resonance Angiography: Principles and Applications is a comprehensive text covering magnetic resonance angiography (MRA) in current clinical use. The first part of the book focuses on techniques, with chapters on contrast-enhanced MRA, time of flight, phase contrast, time-resolved angiography, and coronary MRA, as well as several chapters devoted to new non-contrast MRA techniques. Additionally, chapters describe in detail specific topics such as high-field MRA, susceptibility-weighted imaging, acceleration strategies such as parallel imaging, vessel wall imaging, targeted contrast agents, and low dose contrast-enhanced MRA. The second part of the book covers clinical applications of MRA, with each chapter describing the MRA techniques and protocols for a particular disease and vascular territory, as well as the pathology and imaging findings relevant to the disease state being discussed. Magnetic Resonance Angiography: Principles and Applications is designed to bring together into a single textbook all of the MRA techniques in clinical practice today and will be a valuable resource for practicing radiologists and other physicians involved in the diagnosis and treatment of vascular diseases, as well as biomedical physicists, MRI technologists, residents, and fellows. Editors James C. Carr, MD, is the Director of Cardiovascular Imaging and Associate Professor of Radiology and Medicine at Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA. Timothy J. Carroll, PhD, is the Director of MRI Research and Associate Professor in the Departments of Biomedical Engineering and Radiology at Northwestern University, Evanston, Illinois, USA. Magnetic Resonance Angiography: Principles and Applications is designed to bring together into a single textbook all of the MRA techniques in clinical practice today and will be a valuable resource for practicing radiologists and other physicians involved in the diagnosis and treatment of vascular diseases, as well as biomedical physicists, MRI technologists, residents, and fellows. Editors James C. Carr, MD, is Director of Cardiovascular Imaging and Associate Professor of Radiology and Medicine at Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA. Timothy J. Carroll, PhD, is Assistant Professor in the Department of Radiology at Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA. Editors James C. Carr, MD, is Director of Cardiovascular Imaging and Associate Professor of Radiology and Medicine at Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA. Timothy J. Carroll, PhD, is the Director of MRI Research and Associate Professor in the Departments of Biomedical Engineering and Radiology at Northwestern University, Evanston, Illinois, USA.
Cardiovascular Magnetic Resonance (CMR) is well established in clinical practice for the diagnosis and management of a wide array of cardiovascular diseases. This expertly written source offers a wealth of information on the application and performance of CMR for diagnosis and evaluation of treatment.