Presentation Speech by Professor Torgny Greitz of the Karolinska Medico-Chirurgical Institute

Translation from the Swedish text

Your Majesties, Your Royal Highnesses, Ladies and Gentlemen,

Neither of this year’s laureates in physiology or medicine is a medical doctor. Nevertheless, they have achieved a revolution in the field of medicine. It is sometimes said that this new X-ray method that they have developed – computerized tomography – has ushered medicine into the space age. Well, sometimes, art can adumbrate reality. In his epic poem about the space ship “Aniara,” Nobel Prizewinner in Literature Harry Martinson tells how, one day, the mimarobe, the computer guardian, “…by means of Mima’s formula cycles, phase by phase …saw into the transtomies…” and was able to “…see through everything as though it were glass…”

There, in a single stanza, the poet has captured the essential characteristics and elements of computerized tomography. In addition to X-ray tubes and radiation detectors, the method requires a Mima – that is, a powerful computer; it also calls for a mathematical method, perhaps based on the formula cycles of Fourier transforms, phase by phase; and it produces almost unbelievably clear images of transtomies – that is, cross-sectional views through the human body.

The analogy with the epic poem can be taken even further. The mimarobe remarks: “At this discovery, I went nearly mad…” Few medical achievements have received such immediate acceptance and met with such unreserved enthusiasm as computerized tomography. It literally swept the world. But the enormous procurement costs involved caused some observers to wonder about the mental health of the health-services sector. Indeed, in the United States, a moratorium on computerized tomography was suggested.

What, then, lay behind this spectacular success? Well, to understand something of the background, let us go back to 1895, the year Röntgen discovered X-rays. The very first X-ray photograph Röntgen ever took – of his wife’s hand – indicated, at one and the same time, both the potential and the limitations of conventional X-ray technique. The bones of the hand can be seen, but the complex anatomy of soft tissues – of muscles, tendons, blood vessels, and nerves – does not register.

This inability to distinguish between density differences in the various soft tissues is one of the fundamental limitations of conventional X-ray technique. It means that, in an ordinary X-ray picture, essentially all we can discern are bones and gas-filled spaces. It is the air in the lungs, for example, that enables us to study the lungs’ structure and the shape of the heart.

Conventional X-ray technique has two additional shortcomings that are eliminated by computerized tomography.

One such shortcoming is that structures in threedimensional space overlap in a conventional, two-dimensional, X-ray photograph. What we see is a shadow play – a play, alas, with far too many actors on the stage. It becomes difficult to discern the villain.

The other limitation is that X-ray film cannot indicate any absolute values for variations in tissue density.

Allan Cormack became aware of this latter drawback when, as a young physicist, he was asked to calculate radiation dosages in cancer therapy at Groote Schuur Hospital in Cape Town. He found that the methods then being used – methods based on conventional X-ray examination techniques – were extremely imprecise.

Cormack realized that the problem of obtaining precise values for the tissue-density distribution within the body was a mathematical one. He found a solution and was able, in model experiments, to reconstruct an accurate cross-section of an irregularly shaped object. This was reported in two articles, in 1963 and 1964. Cormack’s cross-section reconstructions were the first computerized tomograms ever made – although his “computer” was a simple desktop calculator.

Cormack realized that his method could be used to produce precise Xray images and so-called positron-camera pictures of cross-sectional “slices” of the body. However, no apparatus for practical diagnostic application of these procedures was constructed.

One probable reason for Cormack’s difficulty in arousing interest in his experiments was that the computers of the time were incapable of executing – within a reasonable amount of time – the enormous calculations the procedure required.

It was Godfrey Hounsfield who brought Cormack’s predictions to fruition. Hounsfield is indisputably the central figure in computerized tomography. Wholly independently of Cormack, he developed a method of his own for computerized tomography and constructed the first clinically usable computerized tomograph – the EMI scanner, which was intended for examinations of the head.

Publication of the first clinical results in the spring of 1972 flabbergasted the world. Up to that time, ordinary X-ray examinations of the head had shown the skull bones, but the brain had remained a gray, undifferentiated fog. Now, suddenly, the fog had cleared. Now, one could see clear images of cross-sections of the brain, with the brain’s gray and white matter and its liquid-filled cavities. Pathological processes that previously could only be indicated by means of unpleasant – indeed, downright painfuland not altogether risk-free examinations could now be rendered visible, simply and painlessly – and as clearly defined as in a section from an anatomical specimen.

Today, computerized tomography is an established method for the examination of all the organ systems of the body. The method’s greatest significance, though, is in the diagnosis of neurological disorders. Since nearly one out of three persons suffers from some disease or disorder of the central nervous system – usually of the brain – during his lifetime, computerized tomography means increased certainty in diagnosis and greater precision in treatment for literally millions of patients.

Cormack and Hounslield have ushered in a new era in diagnostics. Now they, as well as others inspired by their pioneering contributions, are at work developing yet newer methods for the production of images of cross-sections in the body. In those images, we will be able to discern not only structure, but also function; physiology, or biochemistry. In this, new voyages of discovery are being prepared: voyages into man’s own interior, into inner space.

Allan Cormack and Godfrey Hounsfield! Few laureates in physiology or medicine have, at the time of receiving their prizes, to the degree that you have, satisfied the provision in Alfred Nobel’s will that stipulates that the prizewinner “shall have conferred the greatest benefit on mankind.” Your ingenious new thinking has not only had a tremendous impact on everyday medicine; it has also provided entirely new avenues for medical research. It is my task and my pleasure to convey to you the heartiest congratulations of the Karolinska Institute and to ask you now to receive your insignia from His Majesty, the King.