Minimum TR radiofrequency-pulse design for rapid gradient echo sequences

Samy Abo Seada, Anthony N Price, Joseph V Hajnal, Shaihan J Malik
2021 Magnetic Resonance in Medicine  
A framework to design radiofrequency (RF) pulses specifically to minimize the TR of gradient echo sequences is presented, subject to hardware and physiological constraints. Single-band and multiband (MB) RF pulses can be reduced in duration using variable-rate selective excitation (VERSE) VERSE for a range of flip angles; however, minimum-duration pulses do not guarantee minimum TR because these can lead to a high specific absorption rate (SAR). The optimal RF pulse is found by meeting spatial
more » ... ncoding, peripheral nerve stimulation (PNS) and SAR constraints. A TR reduction for a range of designs is achieved and an application of this in an MB cardiac balanced steady-state free-precession (bSSFP) experiment is presented. Gradient imperfections and their imaging effects are also considered. Sequence TR with low-time bandwidth product (TBP) pulses, as used in bSSFP, was reduced up to 14%, and the TR when using high TBP pulses, as used in slab-selective imaging, was reduced by up to 72%. A breath-hold cardiac exam was reduced by 46% using both MB and the TR-optimal framework. The importance of RF-based correction of gradient imperfections is demonstrated. PNS was not a practical limitation. The TR-optimal framework designs RF pulses for a range of pulse parameters, specifically to minimize sequence TR.
doi:10.1002/mrm.28705 pmid:33586800 fatcat:gnbllsovjnby5m62ugm7o7lvre