ABSTRACT
The discovery of nuclear magnetic resonance (NMR) in the 1930s and 1940s was an important step in the history of physics, confirming predictions of the quantum theory of the nucleus. Since these early days, magnetic resonance imaging (MRI) has gone on to revolutionise the practice of medicine, allowing high spatial resolution imaging of both structure and function throughout the body. A good place to start to understand NMR is to consider the meaning of the term ‘nuclear magnetic resonance’ itself. The most obvious feature of an MRI scanner is a large magnet. For the magnetic field strengths used in NMR and MRI, the Larmor frequency lies in the same frequency range as the radiofrequency part of the electromagnetic spectrum. A magnetic field gradient is an additional magnetic field that is applied for a short period of time during the imaging process. Like all magnetic fields, it is a vector.
