X-ray Vision Through Flesh & Bone

Science

27 February 2019
Article
Auteur(s): Philip Lepoutre
Have you ever wondered how an X-ray works?

by David Salazar Marcano  

Contributing Writer

Being able to see what is going on within the human body without having to actually cut someone open is one of the greatest challenges of medical diagnosis. Indeed, this wasn’t actually possible until the discovery of X-ray imaging! This medical imaging technique is now routinely used in most hospitals. But how exactly does it work?

X-ray imaging has actually been around for over a century. It was first discovered by Wilhelm Röntgen on November 8th 1895 who went on to produce the first X-ray image of a human body part in the form of his wife’s hand. In fact, X-rays, so-called at the time due to the unknown nature of the radiation, are also known as Röntgen radiation in his honour in several languages such as German. Furthermore, this discovery was so monumental that it earned Röntgen the first ever Nobel Prize in Physics in 1901.

Now, 250 million X-ray examinations are performed annually in Europe and much has changed since Röntgen’s time. X-rays are no longer considered so mysterious. We now know that they are a type of electromagnetic radiation similar to the visible light emitted from the lightbulb in a flashlight and which we can see every day with our own eyes in the form of colours. However, X-rays are invisible to the eye and they have a much higher energy than visible light, allowing them to pass through solid objects without being absorbed as easily. Hence, they can easily traverse the human body.

Moreover, how easily radiation can go through an object depends on its density and its composition. For example, bones which are much denser than the surrounding body tissue will absorb X-rays more strongly. As a result, if you put photographic film behind a person and then expose them to X-ray radiation not all X-rays will make it through. The areas with no bones will allow the X-rays to pass right through turning the film black, but where there are bones the X-rays will be absorbed and the film will remain white. So, in the end your photographic film will show exactly where all the bones are.

Using photographic film is indeed how it was done at first for many years, but now digital detectors are used more often. These digital detectors can convert the intensity of the incident X-rays into an electrical signal which is then processed by a computer to produce a digital image. What is more, digital technology and a better understanding of X-rays now allows us to see more detail as well as to also observe parts of the body with only low-density body tissue. Such advances are particularly important when trying to detect breast cancer by means of mammography, a form of X-ray imaging.