11/21/2025
The most important discoveries and technical developments often come from unexpected places. One of the most important technological breakthroughs of the 20th century may never have happened were it not for the undirected, curiosity-driven scientific research of the University of Illinois Urbana-Champaign.
Magnetic resonance imaging, or MRI, is an indispensable tool in modern medicine. It gives physicians incredibly detailed images of soft tissue without invasive surgical exams or potentially harmful radiation. Without it, cancer and neurological disorders would be nearly impossible to detect and diagnose at early stages, surgical interventions could not be planned in advance, and research into brain functionality and mental health disorders would not be as accurate or powerful.
And it’s only possible because of fundamental nuclear physics research at Illinois in 1950, 75 years ago.
An Illinois Physics postdoc named Erwin Hahn was investigating the phenomenon of nuclear magnetic resonance, in which certain atomic nuclei – behaving like miniature magnets called “spins” – interact with magnetic fields and radio waves to create detectable signals. It had just been discovered a few years prior, and the laboratory of Illinois Physics professor and National Medal of Science recipient Charles Slichter, of which Hahn was a member, was conducting its own experimental investigations.
Hahn noticed something. Once a collection of spins aligns with a magnetic field, subtle spatial variations in the field strength cause the spins to move out of alignment. He showed that a carefully engineered sequence of radio pulses reverses spin systems back to their original aligned state. The phenomenon was termed a “spin echo” for the system’s apparent return to an earlier state.
With a way of accounting for external field imperfections, it became possible to home in on the interactions between the nuclei themselves. This is responsible for material-specific signals and allows complex systems to be resolved into individual parts.
When medical imaging applications of nuclear magnetic resonance were first explored in the 1970s, its developers observed that the images they obtained were of low quality. They found it necessary to use a spin echo pulse sequence to correct for the inhomogeneities of the magnetic field they were using. The result allowed medical researchers to study spin-spin effects in human tissue and lay the foundations for the high-quality MRI scans we have today.
The most important discoveries and technical developments often come from unexpected places. One of the most important technological breakthroughs of the 20th century may never have happened were it not for the undirected, curiosity-driven scientific research of the University of Illinois Urbana-Champaign.