Wilhelm Röntgen discovered X-rays in 1895.
While experimenting with cathode-ray tubes at the University of Würzburg, Röntgen noticed that a nearby fluorescent screen glowed even when the tube was covered. He concluded that an unknown kind of penetrating radiation was responsible and called it “X-radiation,” with X indicating something unknown.
Röntgen produced an image of his wife Anna Bertha’s hand that showed her bones and wedding ring. The demonstration revealed that the new rays could pass through soft tissue more readily than through bone, creating a completely new way to examine the body without surgery.
The discovery rapidly transformed diagnosis and earned Röntgen the first Nobel Prize in Physics in 1901. X-rays are ionizing radiation, so modern imaging uses carefully controlled doses. X-rays are not the same as ultrasound or MRI, which use sound waves and magnetic fields, respectively.