Broadband 180 degree universal rotation pulses for NMR spectroscopy designed by optimal control

摘要

Broadband inversion pulses that rotate all magnetization components 180degrees about a given fixed axis are necessary for refocusing and mixing inhigh-resolution NMR spectroscopy. The relative merits of various methodologiesfor generating pulses suitable for broadband refocusing are considered. The denovo design of 180 degree universal rotation pulses using optimal control canprovide improved performance compared to schemes which construct refocusingpulses as composites of existing pulses. The advantages of broadband universalrotation by optimized pulses (BURBOP) are most evident for pulse design thatincludes tolerance to RF inhomogeneity or miscalibration. We present newmodifications of the optimal control algorithm that incorporate symmetryprinciples and relax conservative limits on peak RF pulse amplitude for shorttime periods that pose no threat to the probe. We apply them to generate a setof pulses suitable for widespread use in Carbon-13 spectroscopy on the majorityof available probes.