Magnetic Resonance Imaging

IN THE 1920s and 1930s, several physicists measured the newly discovered magnetic properties of nuclei, especially those of the simplest element hydrogen. Among the physicists studying hydrogen were Rabi and colleagues,1whose work led to a Nobel prize in 1944. With Rabi’s group’s findings as a basis and with more refined experimental apparatus, Bloch2and Purcell3subsequently independently measured the magnetic properties of the hydrogen nucleus (a single proton) to an accuracy of 1 ppm, for which they were awarded the Nobel prize in 1952. Bloch and Purcell found that when certain atomic nuclei are placed in a magnetic field and exposed to radiofrequency (RF) energy, they emit a weak radio signal. By analyzing the amplitudes and frequencies of these signals, the chemical composition of the sample can be deduced. By the early 1950s, this approach (termedmagnetic resonance[MR] spectroscopy) had been expanded to permit determination