Conventional MRI assumes one‐photon excitation. That is, for each nuclear spin, a single photon accompanies the transition between energy states. This photon must resonate near the Larmor frequency. In contrast, multiphoton resonances generate MRI signals by using multiple magnetic field frequencies, none of which is near the Larmor frequency. Only the total energy absorbed by a spin must correspond to the Larmor frequency.

Last updated: 2025-09-30