Timeline
1895	X-rays discovered by Wilhelm Roentgen.
1900	Intensifying screens developed by Thomas Edison.
1901	German physicist Christian Helsmeyer discovers that radio echoes can prevent collisions.
1913	"Hot cathode" X-ray tube, W. D. Coolidge.
1915	French professor P. Langevin develops sonar.
1927	Radioactive tracers, de Hevesy.
1930	Rotating anode X-ray tube.
1937	Electron microscope.
1939	Henry Boot and John Randall develop resonant-cavity magnetron.
1940	Radar development begins.
1942	Demonstration of the detection of ships from the air.
1947	John Barker discovered that moving automobiles would reflect radar waves.
1950s	Police began using traffic radar.
1953	Image intensification, Coltman.
1957	Scintillation camera, Anger.
1958	Ultrasound.
1960	Radionuclide generator, Richards.
1970	Emission tomography, Kuhl.
1970s	Realtime, gray-scale ultrasound, Kossoff.
1972	X-ray computed tomography, Hounsfield.
1980	Magnetic resonance imaging, Lauterbur.
1960s	Use of radar in air traffic control.
1960s	Doppler radar.
1970s	Earth-observing satellites begin to use radar to measure Earth's topography.
1990s	A network of over 130 Doppler radar stations is in place in the U.S.
1990s	The Magellan spacecraft maps most of the surface of the planet Venus. The Cassini spacecraft carries radar instruments to study the surface of Saturn's moon Titan.