Introduction

At the start of this book we said that you do not need to understand the workings of the internal combustion engine to be able to drive a car. However, if you're curious, this chapter provides an opportunity to get down and dirty with the innards of the equipment. The basic components of an MRI scanner were introduced in chapter 2. By now you will be familiar with many aspects of MR hardware, especially the use of various coils. In this chapter we provide more technical information. A lot of the detail is in the advanced topics boxes, as many of you will not be especially interested in the engineering and only need a basic understanding. In particular we will see that:

• Magnets for clinical MRI are available with field strengths from approximately 0.2 T to 3 T with even higher field magnets constructed for research purposes. In general higher field strengths give a better signal-to-noise ratio (SNR). Magnets can be classified as either open or closed systems depending on the ease of patient access.

• Four major types of magnets are used in MRI: air-cored resistive magnets, iron-cored electromagnets, permanent magnets and superconducting magnets. Each has advantages and disadvantages in terms of cost, ease of siting, patient and physician friendliness and image quality.

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