On December 30, 1913, Dr William David Coolidge received U.S. Patent No. 1,082,933 on a method for making ductile tungsten for the purpose of making filaments for electric lamps — a task he was assigned when he joined the General Electric Research Laboratory in 1905.

Coolidge developed a way to superheat the metal tungsten in order to draw it out into the fine threads used for lamp filaments. Coolidge then improved the X-ray tube by using a heated tungsten filament cathode in vacuum producing electrons, instead of residual gas molecules in the tube. (U.S. Patent No. 1,215,116). This permitted higher operating voltages, higher energy X rays, and the treatment of deeper-seated tumors.