What medical imaging technique uses high-frequency sound waves?

Ultrasound

Who portrayed mathematician Alan Turing in "The Imitation Game"? What bird's call sounds similar to hysterical human laughter? Who's the first friend to turn thirty? Which act passed in 1941 allowed the U.S. to supply war goods to Allied nations during WWII? Which U.S. city hosted the first World's Fair held in America in 1876, celebrating the country's centennial?