Aspects off the engineering design of whole-body nuclear magnetic resonance machines

Whole-body nuclear magnetic resonance (NMR) machines are being installed at a surprisingly rapid rate in hospitals worldwide. There they are seen as having an imaging sensitivity at least as good as that of CT X-ray scanners with additional capabilities for the display and measurement of flow and of noninvasive chemical analysis for the monitoring of metabolism. The engineering of such machines is demanding, with requirements for great precision, not only from magnets, but also from electronics ranging from direct current to radio frequencies with power levels varying from nanowatts to many kilowatts. The paper reviews the basic physics very briefly, then examines the design requirements and engineering constraints for the major components of a system; although magnet design and construction, a paper in its own right, is not considered here. The paper concludes with a brief resumé of the techniques used, and a short presentation of the type of results that are achieved.