Intended for healthcare professionals

Medical Milestones

Imaging: revealing the world within

BMJ 2007; 334 doi: (Published 04 January 2007) Cite this as: BMJ 2007;334:s12
  1. Adrian M K Thomas, consultant radiologist Adrian.Thomas@bromleyhospitals.nhs.uk1,
  2. John Pickstone, Wellcome research professor2
  1. 1Princess Royal University Hospital, Farnborough Common, Orpington, Kent BR6 8ND
  2. 2Centre for the History of Science, Technology and Medicine, University of Manchester, Oxford Rd, Manchester M13 9PL

    A chance discovery in a physics laboratory opened the body to sight— from bones to molecules—and where the eye has penetrated, the hand is now reaching

    On 8 November 1895 a German physicist, Wilhelm Conrad Röntgen of Würzburg, was investigating the effects of passing electricity through rarefied gases. He was surprised to find that a distant fluorescent screen glowed in the dark. He was amazed when his wife placed her hand in front of the screen and a shadow image of the bones appeared. Röntgen communicated his discovery in a short manuscript entitled “Über eine neue Art von Strahlen” (“On a new kind of rays”), which he submitted to the Würzburg Physical Medical Society on 28 December 1895. He called the rays “X,” because their nature was unknown. In 1901 he was awarded the first Nobel prize for physics.

    In the 19th century many researchers, stimulated in part by the work of Michael Faraday, had studied the passage of electricity through rarefied gases. In England in about 1880 William Crookes had developed an evacuated glass bulb with which he observed “rays” at the negative electrode or cathode. Röntgen was working with a Crookes tube when he discovered his x rays.

    Opening new fields of discovery

    Röntgen's news spread rapidly around the world. The phenomena were readily demonstrable in scientific laboratories and also in public fairs. But classical physics could not explain the rays, and the era of modern physics began—a physics that was based on new understandings of atomic structure.

    In medicine, too, x rays broke old assumptions. The new technology came into its own as an aid to surgery; it was particularly useful for locating needles and bullets and for visualising difficult fractures. X rays were used in the Italo-Abyssinian war of 1896, and in the first world war all the major armies had well organised radiological services. After that war x ray examinations became routine in civilian hospitals, and radiologists became established as medical specialists, now assisted by radiographers.

    By this time, too, more robust tubes were available, and practitioners took precautions against the radiation burns that had cost the hands or lives of many radiological pioneers. But despite awareness of the dangers of radiation, dedicated x ray machines were used in the mid-20th century as an aid in shoe fitting in many high street shops.

    From shadows to slices

    Modern digital radiology was introduced with computed tomography, which has transformed investigative medicine. The British designer of computed tomography, Godfrey Hounsfield, and the South African Allan Cormack were jointly awarded the Nobel prize for physiology or medicine in 1979. In this type of scanning Röntgen's shadows are replaced by detailed, three dimensional images, usually viewed as “slices” through the body. Magnetic resonance imaging and positron emission tomography followed, firstly rendering the body effectively transparent and then revealing the sites of biochemical activity. For example, functional magnetic resonance images can now locate the areas of the brain associated with particular activities, such as listening to music.

    X rays also found many other uses in science and industry, one of which was to prove hugely important for biology and medicine. X ray crystallography was pioneered by William and Lawrence Bragg in Britain; and in Cambridge after the second world war it proved the key to unpacking the structures of nucleic acids and proteins. That was the basis of molecular biology, which by the end of the century had redefined many areas of biomedical research and practice.

    From investigation to intervention

    Shortly after the discovery of x rays their therapeutic potential was realised, and alongside radium treatment they became a mainstay of cancer treatment and palliation. Therapeutic applications continue to develop today, most recently with intensity modulated radiotherapy, which uses a computer to match the beam of x rays to the three dimensional shape of tumours, minimising exposure of the surrounding normal tissue.

    Cardiac catheters, initially used to visualise the coronary arteries in coronary artery disease, are now used to guide interventions such as angioplasty and insertion of stents. Thus radiology has advanced from diagnosis into treatment; it has become a tool used directly by physicians and surgeons. In rich countries, all cancers are imaged before they are treated. Modern medicine can hardly be imagined without imaging. But is this due only to the success of x rays?

    Some recent imaging techniques, notably ultrasonography, arose from technologies outside medicine and might have developed independently of x ray techniques. Computed tomography drew on mathematical principles of interest to several academic disciplines, but it was effectively developed for use with x rays. Magnetic resonance imaging originated in methods used for chemical analysis; but its adaptation to imaging, and the huge investments needed for this, depended on the prior success of computed tomography and hence on that of x rays.

    At the root of sophisticated 21st century medical imaging we find a chance discovery in a 19th century physics laboratory. In transforming physics and later revealing the secrets of biological molecules x rays were the common root of the two great branches of 20th century science. And for medicine the discovery led to an array of visualisation and interventional techniques that permeate modern practice and continue to astonish. Without x rays, doctors, like Röntgen, would be working in the dark.


    • Publication of this online supplement is made possible by an educational grant from AstraZeneca

    • Competing interests: None declared.

    View Abstract