111 years ago today, a physicist by the name of Wilhelm Röntgen caught a glimmer of light coming from a fluorescent screen located across the room from his cathode ray tube setup. The strange phenomenon caught his interest and he spent several weeks investigating the matter.
Röntgen had just "discovered" x-rays. A month later he created the first radiograph (röntgenograms as they were called back then), an x-ray image of his wife's hand. The new rays were a huge hit among physicists, enabling the discovery of all kinds of wonderful things about the properties of matter. Once word reached the medical community of this new discovery, it wasn't long before Röntgen's new rays were used to image and treat patients.
The first x-rays were used to treat a breast cancer patient a mere two months after Röntgen's discovery. Shortly after came Edison's fluoroscope machines for visualizing x-rays in real-time. From there, the rest was history.
Juan A del Regato, Radiological Physicists, American Association of Physicists in Medicine, 1985
Seliger HH, "Wilhelm Conrad Röntgen and the Glimmer of Light", Physics Today, 1995(11), 25-31