chapter  2
10 Pages

Physics of MRI

Since its inception in 1946, nuclear magnetic resonance (NMR) imaging has a›orded an opportunity to noninvasively study the structure and, ultimately, function of tissues from the biochemical or cellular to the macroscopic or organ level. In 1946, Felix Bloch [1] and Edward Purcell [2] independently described that they could manipulate the residual magnetization of spins that are placed in a magnetic œeld by irradiating at a frequency corresponding to the energy di›erence (Larmor frequency) between the high-and low-energy proton spin states. In conjunction with an earlier discovery by Sir Joseph Larmor, they saw that small electromagnetic currents were induced in a nearby radiofrequency (RF) coil, which corresponded to the angular frequency of precession of the nuclei about the œeld and was subsequently named nuclear magnetic resonance.