The British Medical Journal is launching a competition to decided the greatest medical breakthrough.
Present-day medical experts are championing discoveries from the last 166 years.
Adrian Thomas, consultant radiologist at the Princess Royal University Hospital, Kent and John Pickstone, Wellcome Research Professor, Centre for the History of Science, Technology and Medicine, University of Manchester are championing the X-rays and other imaging techniques.
Like many of the other medical milestones, X-rays were discovered by chance.
X-rays are becoming more and more sophisticated
In 1895, German physicist Wilhelm Conrad Roentgen was looking at the effects of passing electrical rays through rarefied gases.
But Dr Roentgen, who was awarded the 1901 Nobel prize for physics, noticed a fluorescent screen in another part of the lab glowed in the dark in the 'X'-rays - and that a shadow image of his the bones of his wife's hand could be seen too.
X-rays became commonplace. They were used in the Italo-Abyssinian war of 1896, and in WWI all the major armies had radiological services.
After the war, X-rays became routine in civilian hospitals. By then, radiologists and radiographers were taking more precautions to protect themselves from radiation burns which had killed or maimed many early workers.
However, X-ray machines were still being used as aids to shoe-fitting in the mid-20th century in many high street shops.
The latter half of the last century saw the development of further types of imaging, including magnetic resonance imaging (MRI) and computerised tomography (CT) scans - introducing 3D rather than 2D images.
Professor Thomas and Professor Pickstone say: "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 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."