The Nobel Prize in Medicine for 2003 rewards the idea that a method used to identify the contents of a test tube could also be used to visualize the contents of our bodies. Magnetic resonance imaging, or MRI, has emerged as a powerful medical accompaniment to X-rays and CT scans, providing strikingly clear pictures of organs such as the brain and lungs. However, its roots lie in the seemingly esoteric world of subatomic particles.
In the late 1940s, Felix Bloch and Edward Purcell discovered nuclear magnetic resonance, or NMR, the concept that certain atomic nuclei behave like microscopic magnets, which can be manipulated by external magnetic fields and radio waves in a manner that can reveal the identity of the atoms in question. Since then NMR has been used to scrutinize the structure of compounds in solution, mainly through detecting the characteristic NMR signals transmitted from the hydrogen atoms that are commonplace in all organic molecules.
An abundant source of hydrogen atoms, of course, is the water molecules that make up most of the content of our cells, and in the early 1970s Paul Lauterbur showed how these could be viewed using NMR signals. Rather than using the stringently uniform magnetic fields researchers traditionally favoured for detecting hydrogen atoms in a sample of molecules, Lauterbur deliberately introduced small variations, or gradients, in the strength of the magnetic field, and he showed that these variations can distinguish hydrogen nuclei in different parts of a sample. Applying these magnetic field gradients in different directions through a sample and combining the resulting NMR signals allowed Lauterbur to construct images that could pinpoint the three-dimensional locations of hydrogen nuclei.
Peter Mansfield further developed efficient ways by which to acquire NMR signals and construct these images; methods that have improved the resolution and speed of MRI to such an extent that images can now be captured in a matter of seconds, not hours. Mansfield’s improvements have provided doctors with the opportunity to view many of life’s essential functions, from the workings of the brain to the beating of a heart.