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H.P. HIGER 1 In the seventeenth century people dreamed about a machine to get rid of evil spirits and obsessions, which were thought to be the main source of mis fortune and disease. I am not going to question this approach, because in a way it sounds reasonable. They dreamed of a machine that would display im ages from the inner world of men which could be easily identified and named. Somehow these are the roots of MR imaging. Of course, we now view disease from a different point of view but our objectives remain the same, namely to make diseases visible and to try to characterize them in order to cure them. This was the reason for setting up a symposium on tissue characterization. About 300 years later the clinical introduction of MRI has great potential for making this dream come true, and I hope that this symposium has con stituted another step toward its realization. When Damadian published his article in 1971 about differences in T1 relaxation times between healthy and pathological tissues, this was a milestone in tissue characterization. His results initiated intensive research in to MR imaging and tissue parameters. Actually his encouraging discovery was not only the first but also the last for a long time in the field of MR tissue characterization.
Quantitative Magnetic Resonance Imaging is a 'go-to' reference for methods and applications of quantitative magnetic resonance imaging, with specific sections on Relaxometry, Perfusion, and Diffusion. Each section will start with an explanation of the basic techniques for mapping the tissue property in question, including a description of the challenges that arise when using these basic approaches. For properties which can be measured in multiple ways, each of these basic methods will be described in separate chapters. Following the basics, a chapter in each section presents more advanced and recently proposed techniques for quantitative tissue property mapping, with a concluding chapter on clinical applications. The reader will learn: - The basic physics behind tissue property mapping - How to implement basic pulse sequences for the quantitative measurement of tissue properties - The strengths and limitations to the basic and more rapid methods for mapping the magnetic relaxation properties T1, T2, and T2* - The pros and cons for different approaches to mapping perfusion - The methods of Diffusion-weighted imaging and how this approach can be used to generate diffusion tensor - maps and more complex representations of diffusion - How flow, magneto-electric tissue property, fat fraction, exchange, elastography, and temperature mapping are performed - How fast imaging approaches including parallel imaging, compressed sensing, and Magnetic Resonance - Fingerprinting can be used to accelerate or improve tissue property mapping schemes - How tissue property mapping is used clinically in different organs - Structured to cater for MRI researchers and graduate students with a wide variety of backgrounds - Explains basic methods for quantitatively measuring tissue properties with MRI - including T1, T2, perfusion, diffusion, fat and iron fraction, elastography, flow, susceptibility - enabling the implementation of pulse sequences to perform measurements - Shows the limitations of the techniques and explains the challenges to the clinical adoption of these traditional methods, presenting the latest research in rapid quantitative imaging which has the possibility to tackle these challenges - Each section contains a chapter explaining the basics of novel ideas for quantitative mapping, such as compressed sensing and Magnetic Resonance Fingerprinting-based approaches
This book is not intended as a general text on MRI. It is written as an intro duction to the field, for nonexperts. We present here a simple exposition of certain aspects of MRI that are important to understand to use this valuable diagnostic tool intelligently in a clinical setting. The basic principles are presented nonmathematically, using no equations and a minimum of symbols and abbreviations. For those requiring a deeper understanding of MRI, this book will help facilitate the transition to standard texts. Chapters 1 through 4 provide a general introduction to the phenomenon of nuclear magnetic resonance and how it is used in imaging. Chapter 1 discus ses magnetic resonance, using a compass needle as an example. In Chapter 2, the transition to the magnetic resonance of the atomic nucleus is made. Chapter 3 describes the principles of imaging. In Chapter 4, the terms T 1 and T 2 are described and their relationship to tissue characterization; the fun damental role of thermal magnetic noise in T 1 and T 2 is discussed.
Magnetic resonance multitasking (MR Multitasking) is a multi-dimensional imaging framework that was developed recently. With low-rank tensor modeling, signal correlation among images at different time dimensions are exploited in MR Multitasking to resolve motion, accelerate image acquisition, and enhance image quality. Though initially developed for cardiovascular imaging, it has also been extended to many other applications, such as whole-brain multi-parametric mapping, free-breathing abdominal dynamic contrast enhanced imaging, etc. The primary focus of this dissertation is to improve two important MR tissue characterization techniques using MR Multitasking: (1) Electrocardiogram (ECG)-less myocardial T1 and extracellular volume fraction (ECV) mapping in small animals at 9.4 T, and (2) Fast 3D chemical exchange saturation transfer (CEST) imaging for human studies at 3.0 T. ECV quantification with cardiovascular magnetic resonance T1 mapping is a powerful tool for the characterization of focal or diffuse myocardial fibrosis. However, it is technically challenging to acquire high-quality T1 and ECV maps in small animals for preclinical research because of high heart rates and high respiration rates. An ECG-less, free-breathing ECV mapping method using MR Multitasking was developed on a 9.4 T small animal MR system. The feasibility of characterizing diffuse myocardial fibrosis was tested in a rat heart failure model with preserved ejection fraction (HFpEF). A 25-min exam, including two 4-min T1 Multitasking scans before and after gadolinium injection, were performed on each rat. It allows a cardiac temporal resolution of 20 ms for a heart rate of ~300 bpm. Elevated ECV found in the HFpEF group is consistent with previous human studies and well correlated with histological data. This technique has the potential to be a viable imaging tool for myocardial tissue characterization in small animal models. CEST imaging is a non-contrast MRI technique that indirectly detects exchangeable protons in the water pool. It is achieved by performing frequency selective saturation at those protons before acquiring water signal readout. CEST MRI provides a novel contrast mechanism to image important physiological information, such as pH and metabolite concentration. However, long scan time is still a crucial problem in many CEST imaging applications, which makes it difficult to translate current CEST techniques into clinical practice. A novel 3D steady-state CEST method using MR Multitasking was developed in the brain at 3.0 T. This allows the Z-spectrum of 55 frequency offsets to be acquired with whole-brain coverage at 1.7 x 1.7 x 3.0 mm3 spatial resolution in 5.5 min. Quantitative CEST maps from multi-pool fitting showed consistent image quality across the volume. Motion handling in moving organs is another challenge for practical CEST imaging. For instance, breath-holding is currently needed in liver CEST imaging to reduce motion artifacts, which limits not only spatial resolution, but also scan volume coverage. Following the whole-brain CEST protocol, a respiration-resolved 3D abdominal CEST imaging technique using MR Multitasking was developed, which enables whole-liver coverage with free-breathing acquisition. CEST images of 55 frequency offsets with entire-liver coverage and 2.0 x 2.0 x 6.0 mm3 spatial resolution were generated within 9 min. Both APTw and glycoCEST signals showed high sensitivity between post-fasting and post-meal acquisitions.
Magnetic Resonance Spectroscopy in Biology and Medicine , presents the experimental and basic aspects of functional and pathological tissue characterization of MRS. A balance is drawn between the basic science, practical technologies and biomedical applications. Covering recent developments in the field: localization, 2D NMR, spectroscopic imaging, data quantification and quality assessment, as well as the basic principles of magnetic resonance spectroscopy, this book provides the lecturer and postdoctoral student, with a valuable research tool for the laboratory. This book is didactically-orientated, with 13 chapters devoted to MRS methodology, 3 chapters on MRS equipment, 13 chapters on clinical and experimental MRS, as well as an appendix containing the basic sciences for MRS and a MRS glossary.