The photo of his wife Anna Bertha's hand bones and ring - made visible by X-rays - is a milestone for very different branches of science. 100 years after the death of Wilhelm Conrad Röntgen, the rays he discovered and used to X-ray the hand are indispensable - and not just in medicine. Researchers use them to reconstruct centuries-old murders, high-intensity X-rays can be used to decode viruses, and X-ray telescopes in space reveal high-energy cosmic processes, for example in black holes.

An X-ray image on a screen in a hospital in Baden-Württemberg shows the left hand of a young person aged between 16 and 19. The radiological examination of the carpal bone and the hand can be used to determine a person's age.

© Felix Kästle/dpa

Today, taking an X-ray image is usually routine and the radiation dose is much lower than it used to be. "We always follow the principle: as little X-ray dose as possible and just as much as necessary," explains Bley, who works with X-rays on a daily basis. According to the Federal Office for Radiation Protection, an estimated 130 million X-ray examinations are currently carried out in Germany every year.

From accidental discovery to standard procedure

Röntgen - born on March 27, 1845 in Lennep, today a district of Remscheid, died on February 10, 1923 in Munich - discovered the rays by chance, late in the evening on November 8, 1895. The scientist was experimenting in Würzburg with electrical discharges in a glass tube pumped almost empty of air (cathode tube). His laboratory was almost dark. Only the generally known luminous phenomena in the tube, visible to the naked eye, dimly illuminated the room. Röntgen covered the tube with black cardboard. And observed that a distant fluorescent screen brightened up.

What's more, when he held his hand between the tube and the fluorescent screen sometime later - he spent around six weeks in the laboratory almost day and night - Röntgen saw the shadow of his hand bones on the screen. This is roughly how it is said to have happened that day, as the Röntgen-Kuratorium Würzburg has gathered.

The association looks after the famous physicist's place of work in Würzburg with original furnishings and equipment. Even Röntgen's desk is still in his old laboratory in the university rooms.

Since then, X-rays have revolutionized many areas of research. It is impossible to imagine medical diagnostics without them - they are used in computer tomography (CT) scanners to examine people slice by slice. According to Bley, the latest development in this area is the photon-counting computer tomograph. This provides even more information and enables more precise diagnoses. "This is phenomenal. I am amazed by the precision every time I see these images." According to Bley, he works with one of the first 20 of these devices to be installed worldwide.

But CT scanners are not only suitable for examining the living. For a study, an international team used the special X-ray procedure to examine three mummies from pre-Columbian South America, which have been kept in European museums since the late 19th century.

The CT scans with the possibility of 3D reconstruction offer unique insights into the body, explains Andreas Nerlich, co-author of the study and Head of Pathology at Munich's Bogenhausen Hospital. In the past, the mummy would have had to be destroyed for such an examination; such detailed diagnostics are not possible with conventional X-rays or older CT scans. The result of the work: the researchers were able to show that the people were murdered.