Medical Physics - X-rays

Within a year of Roentgen's discovery, the Glasgow Royal Infirmary had set up a radiology department and was producing X-ray images of things like a penny stuck in a child's throat and kidney stones. X-rays were also used during the Boer War and First World War to locate exactly where bones had been broken and the site of embedded shrapnel and bullets. In the early 1900s, the damaging properties of X-rays were already being used to fight cancers and skin diseases but it was eventually realised that this was ionising radiation and precautions needed to be taken to protect staff and patients from receiving dangerously high doses.

Now we have come to understand a lot about how X-rays work and how we can utilise them to our advantage. Protection for radiographers (the people who operate the X-ray machines), and allowed safe levels for patients, are well established. The invention of computers has enabled complex machines like Computer Axial Tomography (CAT) scanners to be built. These have an X-ray generator that is mounted in such a way that it can be moved right round the body. It takes X-ray images as it moves and a computer converts the data to three-dimensional images of the inside of the body. Roentgen had used a fluorescent screen in his first experiments which provided 'live' images rather than a photograph. This technique is still used and is now called 'fluoroscopy'. It is often used to examine patients with digestive system problems.

X-rays are a type of electromagnetic radiation that has a much shorter wavelength than visible light. They have the properties of being able to leave an image on photographic film, to be able to pass through opaque solids and they have a range of frequencies - the lower frequencies carry lower energies and are less ionising and less penetrating. More dense materials allow fewer X-rays to pass through so they appear lighter on images whereas less dense materials like skin allow almost all the X-rays through and appear darker.