Naked to the Bone: Medical Imaging in the 20th Century 
by Bettyann Holtzmann Kevles.
Rutgers, 380 pp., $35.95, January 1997, 0 8135 2358 3
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We know the Insides of our bodies intimately. We suffer and enjoy spasms, orgasms, pains, shivers, stomach heaves, heart-beats, knee trembles and twinges. We make guesses about the causes of burps, rumbles, farts, sweats, swellings, flushes and rashes. We may even get a glance, by way of a nasty accident, at a bit of bone. But in other ways we know our insides hardly at all. We are vague about what they look like. Even when we have the words – spleen, kidney and so forth – the associated pictures are often schematic or gleaned from the supermarket meat counter.

It looks as though we don’t want to know. We defend ourselves with squeamishness. The sight of the guts of a road-kill pigeon, let alone of a cat, or, God forbid, ourselves, is nauseating. The heartiness of surgeons and butchers is a self-protecting acknowledgment that even when they break into bodies for the best of reasons, and even when the bodies are not human ones, they are doing something indelicate. An exploration of the dark continent within when it could only be done by way of surgery was about as dangerous a trip as could be made.

Then in 1896, Roentgen discovered X-rays and we became transparent. The world reacted to his announcement with astonishment and delight. It was so wonderfully straightforward: as soon as anyone saw the radiograph of Frau Roentgen’s hand they understood what X-rays did and what they could be used for. If the severity of a fracture or the position of a lodged bullet was to be established, this was the way to do it. But X-rays also put a new distance between us and the reality of our hidden parts. Naked to the Bone is the story of the improvements to medical imaging which have resulted in drawings and photographs of the violated cadavers of the anatomy theatre being replaced by pale shadows, gaudy computer-generated diagrams and grey slice-of-salami-like scans. These say little about the slithery reality of opened bodies. They are produced without violence and we contemplate them with equanimity. The only medical images which still give us a taste of road-kill reality are glimpses on television of fluttering hearts framed in green operating-theatre linen, which go with good news about how we can be reamed, stitched and supplied with spare parts. The terror of the dark interior still lives, but we confront it now in images of war and disaster or in special effects at the movies. Although we have never had so much information available about the insides of living bodies, it is probably fair to say that most of us have never been so protected from the gross facts which hunting, street butchery and public executions used to make plain.

It is not easy to be dissected with dignity. The ancestors of the figures in modern textbooks and encyclopedias, the man and woman in Vesalius’s De Humani Corporis Fabrica, manage it by gesturing eloquently as they are unpacked tripe by tripe. Their classical attitudes clearly label them as art. Francis Bacon turned his back on art when he used a book about positioning X-ray subjects as a source for his paintings. But even these pictures, while not exactly dignified, fit in the heroic/horrific tradition of Rembrandt’s flayed oxen and anatomy lessons. On the other hand, pictures which draw on the new images of X-rays and scans are more melancholic than heroic – genteel reminders of mortality, modern versions of the skulls and bones of old tomb sculpture or skeletons in a Dance of Death. Faces and bodies are art’s most gripping subjects. X-rays and scans offer an alternative to the view from without. The price paid by artists who use them is a loss of access to the subtle and powerful mechanism which makes us so good at distinguishing one body or face from another. The X-ray is a great leveller: we speak of beautiful bone structure, but shown only skulls we are hard put to tell the gross from the gorgeous.

This is probably why some of the connections between medical imaging and works of art that Bettyann Holtzmann Kevles suggests seem shaky, and why, in much of the work which uses them, X-rays and scans are not much more than reminders, of a quasi-Jacobean sort, of the skull beneath the skin. It is easy, too, to push the science/art connection too hard. For example, the Cubists were not ‘the first to portray the transparency and simultaneity of seeing through the body’ – Cubist pictures may show things from different points of view but you don’t see through them, and while Duchamp’s Nude Descending a Staircase is, as Kevles points out, very like one of Marey’s chronophotographs (which show overlapping images of moving figures) it is not at all like an X-ray. To say that Impressionism was ‘produced’ by the ‘study of optics and colour perception’ is to put a very large cart before a very small horse.

The new medical images, by contrast, are powerfully suggestive. The equation of truth with what can be seen – ‘I saw it with my own eyes’, ‘seeing is believing’ – has less force when the deepest speculations about the nature of things involve reconstructing the paths of invisible particles, plots of extra-galactic radio sources and representations of molecules which cannot be resolved by any ordinary microscope. The concept of ‘seeing’ must be revised to include ways of ‘knowing’ shapes which cannot, in any ordinary sense, be seen at all. In this revision, which has affected the whole field of visual information, medical imaging systems have played an important part. From the first it was clear that X-rays are shadow-graphs, not photographs. When other sources of invisible radiation were found, and ways of plotting the information they supplied invented, the results were more like maps or diagrams than pictures. The simple geometry of reflection and refraction which makes it easy for us to grasp the relation between objects and rays of light, retinal images, photographs and even draughtsmen’s versions of what is seen, was no longer relevant. In all sorts of situations the expression ‘I see’ – the end of the argument when photographic evidence is produced – must be replaced by ‘tell me what I am seeing here,’ and the image must be critically examined in case what appears to be structure is a mere artefact, a by-product of the way the data were processed.

X-rays which have passed through the body produce radiographs by darkening a photographic emulsion or making a screen fluoresce. Recorded differently, by sensors which register changes in the intensity of a beam emitted by a source that moves round the body, they are the basis of CAT (computeraided tomography) scans. An ingested radioactive isotope can be tracked as it joins in the metabolic activity of the brain to produce PET (position emission tomography) scans. Molecules, polarised by a very powerful magnetic field, emit radio signals when the field is turned off and they return to a state of rest. Those signals provide information for MRI (magnetic resonance image) scans. And even sound now translates – via ultrasound scans – into pictures.

The outputs from the new imaging machines are processed by the same kind of software and displayed on the same kind of screens as those used by other disciplines – the uninitiated may need captions to tell tumours, radio galaxies and rainstorms apart. It has never been easier, in abstract terms, to think of ourselves as part of the physical world and we have never been more in the hands of experts when we want to understand what the visual evidence implies.

There are scientific, technological, medical and sociological stories to be told about the new medical images. Kevles has a go at telling all of them. The dimensions of the canvas she has chosen are uncomfortably large. No reader is likely to be well-informed about every part of it. I would have traded much of the space given to the use of medical images in the arts for a more concerted attempt to explain, for example, the mathematics of image reconstruction. The treatment of difficult subjects sorts the popularisations of science which describe results from those which give a sense of the thinking that goes into obtaining them. The geometry of image-making is at the heart of any explanation of how the new devices work, yet Naked to the Bone has no diagrams, and the fact that what is surely an MRI scan of the neck seems to be reproduced upside down, or, if it is not, is captioned in a way which makes it almost impossible to work out what is shown, emphasises the degree to which a book that is about images turns its back on visual ways of explaining things.

Some captions are impenetrable to the layman and seem to have been taken straight from the medical literature (‘the infant began to show rapid diffuse hamartomatous malformation’) while an overuse of the dramatic vignette suggests a lack of faith in the inherent interest of technical aspects of the subject: ‘On a hot, humid July morning in 1881, President Garfield arrived early at the old Baltimore and Potomac depot ...’ (He was, of course, shot: Alexander Graham Bell rigged up an electrical machine which failed to find the position of the bullet.) ‘At about the time the Roentgens were celebrating their last quiet Christmas outside the limelight in 1895, young Tolman Cunnings was losing an argument in a Canadian bar’ (he, too, was shot: the lodged bullet was shown in an X-ray and extracted; his assailant was convicted, X-ray evidence was used). Then on to the McKinley assassination (he didn’t have an X-ray, although the apparatus was set up, and died of gangrene eight days after being shot), and yet more forensic examples – a French milkman who was able to demonstrate that he had been shot by a drunk (the bullet was still inside him).

These stories are bathetic – imaging technology does not produce Pasteur-like patient and physician heroics, and even doctors who used themselves as guinea pigs are not figures to put beside pioneers who infected themselves with potentially lethal diseases. In the history of imaging science it is technology, epidemiology and diagnosis that provide the interesting stories. The details of the trials in which the reliability of X-ray evidence was established, and the authority of professional radiographers acknowledged, is only of passing concern.

Kevles finally hits her stride when describing technological economics and politics. The basic science – from Roentgen’s X-rays through to the physics of nuclear magnetic resonance and mathematics of image reconstruction – was the necessary foundation on which the players in the imaging game built. The latter were tinkerers, but tinkerers at the highest level – inventors, doctors, engineers, even, in one case, a patient – who combined fairly original ideas (there were many cases of duplication and some arguments about precedence) with various combinations of energy, luck, ambition, ingenuity and persistence. The arch tinkerer, Thomas Alva Edison, built himself an X-ray machine within four days of learning of Roentgen’s discovery; he made a better tube, found the best material for making screens which fluoresced when struck by X-rays (it made the non-photographic use of X-rays easier, and, when used as an image-intensifier between subject and plate, reduced exposure times). With Edison the dark side of the story makes an early appearance. He noticed burns on his own body, and gave up experimenting with X-rays. The member of his team who specialised in X-ray work, Clarence Dalley, lost all his fingers, then his whole left hand (‘a gloved or amputated hand became the emblem of X-ray workers’), before he died, very painfully, in 1904.

The development of CAT scans is typical of the stories Kevles tells. More than one person had the idea of passing a beam from a moving source through an object and using mathematics to construct an image from readings of variations in the exiting rays. William Oldendorf, an American doctor, set up a model using a gamma-ray source, applied for a patent in 1960 and published his work in 1961. A physicist, Alan Cormack, working first in South Africa and then in America, built an experimental scanner which used a computer to reconstruct images. David Kuhl transmitted the first image of a living human thorax in 1965, using a radioactive source and a computer monitor, while Ronald Bracewell, back in the Fifties, had done work on the mathematics of image reconstruction in the context of radio astronomy. Then, late in the Sixties, EMI entered the arena. A research scientist, Godfrey Hounsfield, picked out pattern recognition from a list of research topics offered when EMI sold the computer division he had been working in. This led to his proposal for a CAT scanner, which eventually became the basis for EMI’s 1968 British patent. A link with the Medical Research Council was established and, as brain scans seemed to offer the greatest potential benefit, it was agreed to develop a suitable instrument. In 1971 the first scan of a patient was made. The woman had to lie still for 15 hours while the source moved round, degree by degree. The results were recorded on tape, processed by computer and photographed off the monitor. Laborious, but successful: a tumour was identified and removed. Other generations of scanners followed – within a few years whole body scans were being done in seconds. EMI’s experience proved that the machines were needed, in the sense that patients and doctors wanted them and that hospitals were able to come up with the half-million or so dollars they cost. They made a lot of money for EMI before the company found the pace too hot and left the field to those whose main business was in medical instruments. In this case, as in others, it was money, not ideas, that set the pace of development, and a harnessing of several disciplines (computing, physics, medicine) which made them possible.

CAT and MRI machines are wonderful instruments. They are also very expensive. Justifying the expense of new ones, as Kevles explains, is not as straightforward as you might think. If you have had a tumour successfully diagnosed and removed, or been spared the trauma of investigative surgery, you will bless them. Because they allow a beam of radiation to be directed at malignant tissue they have made non-invasive intervention as well as exploration possible. On the other hand, they may have encouraged an indulgence in, and reliance on, expensive tests in an environment where resources are finite. What has been revealed by the new machines is fascinating in itself, but it will take a lot of epidemiological work to decide whether the great benefits which scans have brought in acute cases can be extended. Some people believe that mass screenings may do more harm than good. Kevles describes a situation in which the impetus to develop new systems for body imaging is fading. The funds needed to take the next step may not be easy for a government to justify or for private medical suppliers to find out of their profits. She compares the problems to those of space exploration: the machine which (for example) would let a doctor ‘feel’ in a reconstructed body image for an invisible area of hard, cancerous tissue may, like manned missions to Mars, have to wait.

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Vol. 19 No. 16 · 21 August 1997

Peter Campbell’s piece on medical imaging (LRB, 31 July) expressed a wish to know more about the mathematics of tomography. The problem is to reconstruct an image of a slice through a body from a set of readings, known as projections, taken as an X-ray source and detector are routed in a circle around the slice. If we know what is in a body we can calculate what will happen to an X-ray that passes through it. The problem here is the inverse – given the X-ray data, determine what is in the body through which it passed – and is, in the language of mathematics, ill-posed: it may not admit of a unique solution. There was, however, an approach to this kind of problem developed by an Austrian mathematician called Radon, 56 years before the inception of tomography.

The theorem deals with the Fourier transform of the image: the set of elementary wave-like patterns, each defined by a frequency, an amplitude and an orientation, which if superimposed would produce the image. The theorem states that the Fourier transform of the one-dimensional projection at each position of the detector forms one line through the two-dimensional Fourier transform of the image we seek to construct. So, if we have Fourier transforms of enough projections, we will have a set of lines from which we can assemble the Fourier transform of the image we require. There is a well-known equation for deriving an image from its Fourier transform. Rejigging this using the theorem, one can derive an equation which has two parts, corresponding to a two-stage process for image reconstruction: filtering and back-projection. The second stage is easy to explain: think of each X-ray as a jet of some kind of magic ink that can pass easily through air, less easily through tissue and hardly at all through bone, and imagine that the detector is a sponge which absorbs only the ink which passes in a straight line through the slice. Back-projection is equivalent to dragging the sponge across a sheet of paper in the direction corresponding to that travelled by the X-ray, so that all the ink in the sponge is transferred smoothly to the paper. If an exposure was taken for every possible line through the slice, the pattern of ink built up on the paper would be an (admittedly pretty ropey) image of the way ink was absorbed in the slice: which bits were bone, which were tissue and so on. The first stage can be thought of as a process which produces ‘filtered’ data suitable for back-projection, by combining the Fourier transform of the projection data with a mathematical function, the definition of which is neither perspicuous nor intuitive.

The calculations involved are not exactly the stuff of mental arithmetic and the rendering of the relevant acronym as Computer Assisted Tomography perhaps understates the contribution of the computer. The OED prefers Computerised Axial Tomography but the process is now universally known as CT. A much more exciting development in medical imaging acronyms is the addition of a lowercase ‘f’ before MRI. In MRI, as in CT, stacks of two-dimensional images form a three-dimensional representation of anatomy. Such scans can now be completed at a speed which allows the charting of fluctuations over time, enabling the reconstruction of images which are no longer representations of static anatomy but which visualise anatomical function. The promise of fMRI (functional Magnetic Resonance Imaging) is that we might be able not just to look inside a French milkman, but to see what he is thinking. Or at least the impact that his mental life is having on his cerebral blood flow. Such is our curiosity about this topic that it now attracts the kind of funding Peter Campbell worries might be lacking for medical imaging research.

Paul Taylor
UCL Medical School,

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