Raymond Damadian
Damadian received a National Medal of Technology in 1988 and was inducted into the National Inventors Hall of Fame in 1989. His original MRI full-body scanner was given to the Smithsonian Institution in the 1980s and is now on loan and on display at the National Inventors Hall of Fame in Ohio. In 2001, the Lemelson-MIT Prize Program bestowed its $100,000 Lifetime Achievement Award on Damadian as "the man who invented the MRI scanner."
Magnetorotational instability
The MRI was first noticed in a non-astrophysical context by Evgeny Velikhov in 1959 when considering the stability of Couette flow of an ideal hydromagnetic fluid. His result was later generalized by S. Chandrasekhar in 1960. This mechanism was proposed by Acheson & Hide (1973) to perhaps play a role in the context of the Earth's geodynamo problem. Although there was some follow-up work in later decades (Fricke, 1969; Acheson and Hide 1972; Acheson and Gibbons 1978), the generality and power of the instability were not fully appreciated until 1991, when Balbus & Hawley gave a relatively simple elucidation and physical explanation of this important process.