Optimal control design of band-selective excitation pulses that accommodate relaxation and RF inhomogeneity

TL;DR

This paper develops an optimal control method for designing band-selective excitation pulses that are robust against relaxation and RF inhomogeneity, significantly improving signal retention and selectivity in NMR applications.

Contribution

It introduces relaxation-compensated, frequency-selective pulses (RC-SEBOP) that improve robustness and performance in the challenging regime where T1 and T2 equal the pulse length.

Findings

Significant reduction in signal loss with optimized pulses

Nearly ideal frequency selectivity achieved

Simple sequence elements eliminate residual signals

Abstract

Existing optimal control protocols for mitigating the effects of relaxation and/or RF inhomogeneity on broadband pulse performance are extended to the more difficult problem of designing robust, refocused, frequency selective excitation pulses. For the demanding case of T1 and T2 equal to the pulse length, anticipated signal losses can be significantly reduced while achieving nearly ideal frequency selectivity. Improvements in performance are the result of allowing residual unrefocused magnetization after applying relaxation-compensated selective excitation by optimized pulses (RC-SEBOP). We demonstrate simple pulse sequence elements for eliminating this unwanted residual signal.