Magnetic Resonance Imaging

Physical Principles and Sequence Design

Robert W. Brown, Y.-C. Norman Cheng, E. Mark Haacke, Michael R. Thompson, Ramesh Venkatesan

• Publisher: Wiley-Blackwell
• Year: 2014
• ISBN:
  9781118633977
• Edition: 2
• Topic: Medicine
• Subtopic: Radiology, Radiotherapy & Nuclear Medicine

New edition explores contemporary MRI principles and practices

Thoroughly revised, updated and expanded, the second edition of Magnetic Resonance Imaging: Physical Principles and Sequence Design remains the preeminent text in its field. Using consistent nomenclature and mathematical notations throughout all the chapters, this new edition carefully explains the physical principles of magnetic resonance imaging design and implementation. In addition, detailed figures and MR images enable readers to better grasp core concepts, methods, and applications.

Magnetic Resonance Imaging, Second Edition begins with an introduction to fundamental principles, with coverage of magnetization, relaxation, quantum mechanics, signal detection and acquisition, Fourier imaging, image reconstruction, contrast, signal, and noise. The second part of the text explores MRI methods and applications, including fast imaging, water-fat separation, steady state gradient echo imaging, echo planar imaging, diffusion-weighted imaging, and induced magnetism. Lastly, the text discusses important hardware issues and parallel imaging.

Readers familiar with the first edition will find much new material, including:

• New chapter dedicated to parallel imaging
• New sections examining off-resonance excitation principles, contrast optimization in fast steady-state incoherent imaging, and efficient lower-dimension analogues for discrete Fourier transforms in echo planar imaging applications
• Enhanced sections pertaining to Fourier transforms, filter effects on image resolution, and Bloch equation solutions when both rf pulse and slice select gradient fields are present
• Valuable improvements throughout with respect to equations, formulas, and text
• New and updated problems to test further the readers' grasp of core concepts

Three appendices at the end of the text offer review material for basic electromagnetism and statistics as well as a list of acquisition parameters for the images in the book.

Acclaimed by both students and instructors, the second edition of Magnetic Resonance Imaging offers the most comprehensive and approachable introduction to the physics and the applications of magnetic resonance imaging.

Chapter 1
Magnetic Resonance Imaging: A Preview

Chapter Contents

1. 1.1 Magnetic Resonance Imaging: The Name
2. 1.2 The Origin of Magnetic Resonance Imaging
3. 1.3 A Brief Overview of MRI Concepts

Introduction

The primary purpose of this chapter is to provide a succinct overview of the basic principles involved in the process of using nuclear magnetic resonance for imaging. This overview is in the form of a list of results, without derivation, in order to provide a story line and goals for the reader to follow in the detailed treatment of this material in the coming chapters.

The chapter begins with an explanation of the name, ‘magnetic resonance imaging,’ or MRI, followed by a short and inadequate history¹ of some of the developments that led to the discovery of key imaging concepts. The third, and largest, section is a preview of the subsequent twenty-seven chapters. Finally, some relevant reference texts and articles are listed in the Suggested Reading at the end of the chapter.

1.1 Magnetic Resonance Imaging: The Name

Magnetic resonance imaging is a relatively new discipline in the realm of applied sciences. A main thrust has come from the imaging of soft tissues in the human body and metabolic processes therein, such that it occupies a strong position in biomedical science applications. MRI is a powerful imaging modality because of its flexibility and sensitivity to a broad range of tissue properties. One of the original reasons for the excitement about MM was. and continues to be, its relative safety, where the ‘noninvasive’ nature of the magnetic fields employed makes it possible to diagnose conditions of people of almost any age. Today MM also offers great promise in understanding much more about the human body, both its form and its function.

MRI stems from the application of nuclear magnetic resonance (NMR) to radiological imaging. The adjective ‘magnetic’ refers to the use of an assortment of magnetic fields and ‘resonance’ refers to the need to match the (radio)frequency of an oscillating magnetic field to the ‘precessional’ frequency of the spin of some nucleus (hence the ‘nuclear') in a tissue molecule. It might be more accurate to refer to this field as NMM rather than MM, but there is widespread concern over any phrase containing the word ‘nuclear.’ Although the nuclear component simply refers to a benign role of the ‘spin’ of the nucleus in the process, the word has been suppressed and the public and the profession have embraced the MM acronym.

1.2 The Origin of Magnetic Resonance Imaging

To describe the history of any technological advance in a given field is a very difficult and sensitive issue; to offer a brief and incomplete account is fraught with peril. Still, the beginning student may be aided and inspired by even a short historical discussion. It may be said that MM had its beginnings in 1973 with the seminal papers by Lauterbur and Mansfield. It was already well known that the intrinsic angular momentum (or ‘spin’) of a hydrogen nucleus (the proton) in a magnetic field precesses about that field at the ‘Larmor frequency’ which, in turn, depends linearly on the magnitude of the field itself. Their idea was very simple. If a spatially varying magnetic field is introduced across the object, the Larmor frequencies are also spatially varying. They proposed and showed that the different frequency components of the signal could be separated to give spatial information about the object. This key point of spatially encoding the data opened the door to MR imaging. Others also recognized the importance of this area, with early attention brought to tumor detection by Damadian.

Something may be learned here by the beginning student. Often the basic step toward new developments, which may become quite complicated as a whole, is a simple connecting idea. The concept of using a magnetic field gradient was one such ‘aha’ that captured the essence of MRI as it is practiced today, much like the coupling of the nuclear spin of the proton to the magnetic field was the key to the early experiments by both Bloch’s group and Purcell’s group in their pioneering work in NMR.

The c...