The scientific principles of magnetic resonance imaging (MRI) stem from those of nuclear magnetic resonance (NMR; Milestone 8); however, now, especially in the mind of the public, the latter lies very much in the shadow of the former. The technological jump from NMR spectrum to MR image began in the early 1970s, and subsequent developments have established MRI as a priceless technique in medical research and diagnostics.
MRI uses magnetic fields and radiowaves to produce, in a non-invasive manner, 'tomographic' images of a three-dimensional object. Paul Lauterbur introduced the scientific basis behind this mode of visualization as "image formation by induced local interactions". His idea was to combine two magnetic fields, so that one induces an interaction whereas the other restricts this interaction to a localized region in space. He proposed the term 'zeugmatography' to describe the technique, from a Greek word meaning 'that which is used for joining'; however, the name never became widely accepted.
Lauterbur's pioneering experiment involved the imaging of a cross-section through two glass tubes of ordinary water (H2O) attached to the inside wall of a larger tube of deuterated water (D2O). A two-dimensional image showing the location of the tubes of H2O was generated by combining four projections taken from different angles around the set-up.
Some scepticism surrounded this initial observation. It seemed counterintuitive that radiowaves could be used to image objects that were much smaller than their wavelength. Yet it was because the interactions were restricted to certain regions that, in fact, the technique became independent of wavelength.
Lauterbur recognized the potential of the concept at the time of the first simple experiment. He believed it could be used to investigate complex systems and noted the possibility of visualizing biological tissues — in particular, distinguishing between malignant tumours and healthy tissue. Many of the early practical developments in MRI were made by Peter Mansfield, who discovered how to acquire images rapidly. In recognition of their contributions, Lauterbur and Mansfield shared the 2003 Nobel Prize in Medicine.
The invention of MRI has not been without controversy. Others have claimed to have produced the first 'NMR image', most notably Raymond Damadian, who had reported in 1971 the ability to distinguish between normal tissue and tumours using magnetic resonance. On the announcement of the prize, he fervently disputed the decision of the Nobel committee.
The unquestionable fact remains that, although the invention of MRI — with its marriage of magnetic fields — took scientists by surprise at its conception, in its more recent lifetime it has proved to be an invaluable tool for the medical world.
