If, while exposed to the magnetic field, the precessing nuclei are also hit with a radiofrequency (rf) pulse, they will absorb and re-emit energy at specific frequencies according to their rate of precession.

• 当暴露在外界磁场中的时候，旋进的原子核也会被射频脉冲击中，它们会吸收并且根据旋进率再释放特殊频率的能量。