By using magnetic fields to manipulate nuclear spins, magnetic resonance imaging excels at revealing subtle features in soft tissue. RF pulses excite the hydrogen nuclei in muscle, fat, or nerve fibers, say, that are aligned in a static magnetic field. When the RF frequency of the pulses matches the resonance, or Larmor, frequency, the spins tip and precess about the static field. Thanks to Faraday induction, the precessing magnetic moment then gives rise to an electromotive force that can be detected in a nearby coil of wire.
Typically, one coil transmits the RF pulses and another detects the induced signals, with both coils held close to the body to exploit the short-range coupling. That configuration has been used in clinical settings for decades, most often with imagers built using 1.5-tesla magnets.
But in recent years, medical imagers have been developed with magnetic fields exceeding 9 T. The signal-to-noise ratio scales...
