Magnetic fields varying at radio frequency (RF) are fundamental to nuclear magnetic resonance (NMR) and the related technique of magnetic resonance imaging (MRI). In NMR, RF fields are used in conjunction with a strong, constant magnetic field to excite hydrogen nuclei in water into precession. The precessing nuclei in turn generate an RF magnetic-field oscillation - the NMR signal. In almost all MRI experiments, the RF field is generated by a coil of wire - the RF coil - and the nuclear precession is detected by electromagnetic induction in a similar coil. But excitation and detection of the NMR signal require that the RF coils lie in close proximity to the human body because it is the short-range signals (the near fields) that are exploited in the interaction.rnIn a radical rethink of the experimental set-up used for MRI, Brunner et al. (page 994 of this issue) now show that this conventional approach based on RF coils can be replaced by one that uses travelling radio waves in a long-range interaction with the sample, offering more-uniform coverage of larger samples. What's more, by freeing up space in the bore of the scanner, this innovative approach could make the scanning experience more comfortable for human patients.
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