NMR spin doctors

Nuclear magnetic resonance is a physical phenomenon which has had major impact in two other fields, chemistry and medicine, and this encyclopedia has been published to celebrate the 50th anniversary of its discovery.

Although I. I. Rabi had been awarded the Nobel prize in 1944 for his "resonance method for recording the magnetic properties of the atomic nucleus", this resonance phenomenon was first properly demonstrated (independently) by Edward Purcell at Harvard and Felix Bloch at Stanford, for which they were awarded the Nobel prize for physics in 1952.

The paper by Bloch (dated January 29 1946) is a classic Nobel prize-winning short paper (like that on the discovery of radioactivity) in that it comprises only 267 words. Rabi's original paper (January 31 1938) also fits on a single page, but Purcell (December 24, 1945) was rather more garrulous. Bloch (and hence Varian) cleverly obtained the first patent. The initial major impact of Purcell and Bloch's discovery was in chemistry, but later on, with the development of imaging methods based on NMR, medicine has also benefited.

It is interesting to note that as the word "nuclear" became more and more synonymous with "nasty", the medical imaging application became renamed Magnetic Resonance Imaging (MRI) so as not to frighten patients, although some still do ask for the NMR (pronounced "enema") unit, with curious results. As with X-ray based computerised tomography (CT), much of the development of MR imaging methods took place in the UK, but since then it has been dominated industrially by the major multinationals such as Siemens, Philips, Toshiba etc.

This impressive (and also weighty) encyclopedia is in eight volumes and totals 6,000 pages. The first volume gives an historical perspective, the rest contains a series of short articles in conventional alphabetic order, with contributions from about 600 authors.

The list of contributors looks like a Who's Who? of the subject, and it is pleasant to see that many of the articles were written by British authors, many of them friends and colleagues (aka the "Spin Doctors"). These short papers are quite up to date (1994) but given the rapid evolution of the subject, are likely to "decay" rather rapidly.

The historical review is the most entertaining part of the book, although some dramatic moments have been expurgated or toned down. In medical use, although the technique is believed to be completely safe, it has been suggested (as a joke) that maybe there are some unexpected psychological effects. Many of the key medical developments were performed by the inventors scanning their own brains, and some of them are a pretty rum bunch. A nice quote from Purcell is given: "I remember in the winter of our first experiments, just seven years ago, looking on snow with new eyes. There the snow lay around the doorstep, great heaps of protons quietly precessing in the earth's magnetic field. To see the world for a moment as something rich and strange is the private reward of many a discovery. But I'm afraid it has little bearing on the sober question which we must, as physicists, ask ourselves: what can we learn from all this about the structure of matter?"

This calm and philosophical approach is in contrast to later events when commercial competition became severe. I remember a presentation where one of the inventors in the field compared the significance of his work to that of Moses, Jesus Christ and Napoleon, somewhat to the surprise of the audience! In between these extremes, a number of stories from laboratory work are cited in the book. One example is when David Hoult (originally from Oxford but then working at the NIH in Washington) tripped, let go of a large steel bar which flew at his colleague Dooey Lee and passed "with great speed and precision between his legs without touching him" into the magnet. While events such as near castration are fortunately rare, the reader gets a good feeling for the boredom of much of scientific research, suddenly resulting in the Eureka moment of joy when something finally works.

The bulk of the encyclopedia comprises short scientific articles on NMR applications, some taken from chemistry, many taken from medicine and some from other disciplines such as botany and geology. Both principles and applications are included. Fortunately a good index permits the identification of most specific topics. The coverage is comprehensive; I noted only a few topics omitted, one example being that of imaging without an external magnet in the earth's magnetic field. Another omission is that of a good cross-referenced list of pulse sequence names.

In general, the articles are mostly self-contained. The level is appropriate for research workers in the field, and in certain cases, could be used as an introduction for students. Reasonable mathematical detail is sometimes included.

Where to now? How big can we expect the encyclopedia to be on the 100th anniversary, 200 CD-Roms? Some hints are suggested. Historically, the problems that held NMR back were the lack of precision (for example resolution) and the speed of data acquisition. Several advances contributed to their being overcome: progress in electronics, for example pulsed MR, advances in methodology, such as sample spinning, better magnets, such as superconducting magnets, and especially better data processing, initially in the use of the Fourier transform, later, the digital handling of the whole acquisition and analysis process. Smart methods, such as Echo Planar Imaging have been discovered to shorten (imaging) acquisition times very significantly, as Sir Peter Mansfield has reminded us over the years.

But can this progress be maintained? I think the answer is yes. The basic ingredients of any NMR system are a magnet, some electronics, a computer, and an appropriate application. Thus we might expect costs to decrease, and availability to increase. In radiology, the question is often asked, will MRI replace the use of the CT scanner? The answer again is increasingly yes, especially for soft tissue lesions. Can additional data be extracted? Again a positive answer is illustrated by the progress made in Magnetic Resonance Spectroscopy (MRS) in vivo, and by the progress in so-called functional imaging (as illustrated at the Institute of Neurology and University College London). Assessment of tissue, for example, after a stroke, using diffusion-weighted techniques are examples of problems which are now being addressed in the medical field, and given greater availability of the technique, could make significant medical impact. The use of open magnets for surgical intervention under NMR guidance is also very important. The widespread use of this method in chemistry and improvements in techniques are also evident. Such subjects are well covered in this encyclopedia. Finally a topical example (Euro 96) may be given of the value of the imaging method: that of assessing brain status after repetitive mechanical blows to the head, such as undergone in boxing and football, where changes in brain size and function would be expected. It is clear that the method in general is far from reaching its limits. Perhaps we may expect a portable MRI examination of football players after spectacular fouls in the near future.

But who will write the next encyclopedia? The contributors here are mostly from the US and the UK, and mostly from universities. This in part reflects the important contributions to the development of the subject of academics, for instance in the imaging field the teams at the Universities of Nottingham and Aberdeen.

This resulted in the past in many successful patents being granted and created the initial strength of EMI and Picker in exploiting these inventions; a notable success story of academic work leading to commercial value.

What we have seen since, as a result of the scale of investment involved, has been a transfer of the basic research from universities to industry, from nationals to multi-nationals, and out of the UK. My hunch (fear?) is that the next editors (as well as many of the contributors) may have Chinese names.

Who will read this encyclopedia? Many workers and students in the field will find much of value here. But who will purchase this encyclopedia? Only a few libraries (and few university libraries) will be able to afford it. Maybe some of the great British scientists involved, presumably in receipt of their well-deserved royalties, would like to reread, perhaps with wry amusement, of their roles in this great scientific success story of the last few decades. Good vibrations, from Harvard and California, indeed!

Andrew Todd-Pokropek is professor of medical physics, University College London.