Local SAR reduction in multi-slice pTx via SAR-hopping between excitations

摘要

Described here are a system and method for designing radio frequency (“RF”) pulses for parallel transmission (“pTx”) applications, and particularly pTx applications in multislice magnetic resonance imaging (“MRI”). The concept of “SAR hopping” is implemented by framing the concept between slice-selective excitations as a constrained optimization problem that attempts designing multiple pulses simultaneously subject to an overall local SAR constraint. This results in the set of RF waveforms that yield the best excitation profiles for all pulses while ensuring that the local SAR of the average of all pulses is below the regulatory limit imposed by the FDA. Pulses are designed simultaneously while constraining local SAR, global SAR, and peak power, and average power explicitly.

主权项

1. A method for designing parallel transmission (pTx) radio frequency (RF) pulses for use in multislice magnetic resonance imaging (MRI), the steps of the method comprising:
a) determining a target magnetization to be achieved in a plurality of slice locations in a subject; b) selecting a set of compressed specific absorption rate (SAR) matrix points at which SAR can be evaluated; c) designing a plurality of RF pulses for achieving the target magnetization by determining a set of RF waveforms that minimize an average local SAR of the plurality of RF pulses evaluated at the compressed SAR matrix points; and d) making the plurality of RF pulses designed in step c) accessible to an MRI system to perform multislice MRI.