Daily Science

On 8 November 1895, Wilhelm Röntgen discovered an unknown type of electromagnetic radiation. He called this radiation X-rays, using the mathematical symbol x to represent something unknown. Not only did he win the first Nobel Prize for his work in 1901, he also ushered in a new era in medicine, one where it was no longer necessary to cut open the body to investigate an ailment. In fact, he unwittingly realized this potential early on when he used his wife’s hand to make the first X-ray image. With the devastation of World War I and II, X-rays became widely used and have become a vital instrument for doctors and dentists ever since.

Compared to today, medical diagnosis in the late 1800s was very primitive. To investigate ailments, doctors were limited to their own five senses. The senses of sight and smell were able to detect exterior signs of disease. (We hope they didn’t taste their patients too often.) Investigating the interior without dissection the body was more difficult. The sense of touch helped with broken bones or foreign objects lodged within the body, but swelling at the site could make diagnosis difficult. Aiding hearing, the stethoscope magnified sounds in the body. However, diagnoses relying on touch or sound were always dependent on a mental image the doctor created of the patient’s innards. And this mental map could look quite different from reality.

With X-rays, however, doctors could make a real image of a patient’s insides, which, as you can imagine, greatly improved medical treatment.

In our post about archaeology, we mentioned the electromagnetic spectrum and some uses of infrared radiation — radiation with wavelengths slightly longer than visible light. In this post, we jump to the other end of the electromagnetic spectrum. X-rays have wavelengths much shorter than visible light.

In order to make an X-ray image of a patient’s insides, doctors first need a source of X-rays. To make X-rays, a heated piece of metal called the cathode, and a collector — a metal plate called the anode — are placed within a glass tube from which all the air has been removed. The cathode and anode are connected to a high voltage power source and a beam of electrons is created in the tube between the cathode and anode. X-rays are produced when electrons hit the anode. This setup, called an X-ray tube, is nearly identical to the cathode-ray tubes used in older television sets and computer monitors. (In fact, the word set refers to the set of cathode-ray tubes making up the television.)

In medical uses, a tube like this is used to create short pulses of X-rays that are aimed at the patient. Some photographic film is placed behind the patient. X-rays are blocked somewhat by denser materials like bones and pass more easily through less dense materials like tissues. A shadow forms on the film where X-rays are blocked. When developed, the film turns darker where more X-rays have hit it, so denser objects like bones appear lighter on the final X-ray.

As useful as this simple technique is, more advanced techniques have also been developed. A CT (computed tomography) scan, for example, is a series of images made by passing the X-ray tube in a circle around a patient. Thousands of images are made from many directions and these images are then compiled to form a 3D image.

Now, the next time you visit the dentist, or go through security at an airport, or break a bone, you can thank Mr Röntgen for his discovery!