Peter Mansfield - Nobel Lecture

The topic of magnetic resonance imaging (MRI) started for us at Nottingham in the early summer of 1972. During a discussion with one of my graduate students, Peter Grannell and my post-doc Dr Allan Garroway, concerning multiple-pulse line narrowing experiments in solids, the idea occurred to me to use the line narrowing technique as a means of effectively removing dipolar interactions in a material like CaF2 and at the same time impose an external linear gradient on the sample thus broadening the line shape to reveal the atomic or molecular structure within the sample. It soon became apparent, however, even with the achievable narrowed linewidths of around 1 Hz for CaF2, corresponding to a line width reduction of 3 104, that the residual line width was still too broad using practical external gradients to resolve the atomic structure in a single crystal of CaF2. Despite this setback, work continued with artificial one-dimensional lattices made up of several thin plates of camphor. Peter Grannell and I continued this work during the course of 1972 and it resulted finally in a paper presented at the First Specialized Colloque Ampère, Krakow in 1973 (1). Formal publication appeared shortly after (2). These papers emphasized the Fourier transform approach used, even though the images of the camphor stacks were one-dimensional. It was clear that we had made our task much more difficult by choosing to work with solids. Thoughts rapidly turned to liquid-like spin systems where the line narrowing approach would be unnecessary. The imaging approach considered so far was essentially one or two-dimensional. The next step was to define a thin slice of material so that this would be imaged without spill over to adjacent planes. This was achieved using a technique called selective irradiation (3). One of the major practical difficulties encountered with MRI to this point was the time it took to acquire the data. Line-scanning, for example, took typically 10–20 min to acquire an image comprising 64 64 pixels (4). The breakthrough came in 1977 with the introduction of echo-planar imaging (EPI) (5). This snap-shot technique meant that in principle complete two-dimensional images could be achieved in extremely short times