MRI RF Pulse Spectral Regrowth Contributions by PIN Diodes

Spectral regrowth is a concern to the MRI system designer because of the potential for RF pulse distortion and subsequent excitation of nuclei outside of the region of interest. Previous work on spectral regrowth produced by series-connected PIN diodes has focused on their influence in communication systems but to the author's knowledge, no work to date has studied this spectral regrowth in MRI applications. This paper looks at the contributions of PIN diodes following MR power amplifiers in the generation of adjacent channel power, focusing on the RF slice select pulse. The analysis shows how PIN diode nonlinearities influence spectral regrowth and how the PIN diode operating conditions affect the out of band components.