Introduction

Since the first image of the human wrist was obtained by Paul Lauterbur in 1972, magnetic resonance imaging (MRI) has developed significantly to a stage where it has found applications to most of the speciality branches in medicine. In the last decade there has been a rapid development in gradient and RF coil technology and this has resulted in the implementation of fast imaging techniques such as echo planar imaging (EPI), on clinical imaging systems. It is now possible to acquire a single image of the brain in less than 50 ms using EPI. During this period, MR has been used for obtaining functional information about the different physiological processes in the brain, such as diffusion and perfusion. This has resulted in the development of newer techniques, with the MR systems being equipped with faster gradients. MRI has been used in the acute stroke setting over the past few years, due to the unique sensitivity of several new MRI techniques to rapidly detect cerebral ischemia. These new techniques include diffusion-weighted imaging (DWI), perfusion-weighted imaging (PWI), magnetic resonance spectroscopy (MRS) and high-speed MR-angiography (MRA). In this chapter, we will briefly outline the basic physical principles of MRI, which will lay a foundation for the following chapters. A brief overview of the MR techniques that have been developed for investigating stroke patients is provided. It is assumed, however, that the reader is familiar with the basic physics of MRI.