1. Radiology, the branch of medicine concerned with radioactive substaces, including x-rays, radioactive isotopes, and ionizing radiations, and the application of this information to prevention, diagnosis, and treatment of disease.
2. Radiology, the science of radiation and, specifically, the use of both ionizing (like X-ray) and nonionizing (like ultrasound) modalities for the diagnosis and treatment of disease.

Roentgenology is named for Wilhelm Conrad Roentgen who discovered X-rays. Roentgen, a professor of physics in Germany, wanted to prove his hypothesis that cathode rays could penetrate substances besides air.

When he saw that he could film his thumb and forefinger and their bones on a screen, the story goes that he replaced the screen with a photographic plate and X-rayed his wife's hand.

Roentgen's report of his findings, "On a New Kind of Rays", was published by the Physical-Medical Society of Würzburg, Germany, in December 1895.