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

• Published in: Journal of magnetic resonance (1997) Vol. 217; pp. 53 - 60
• Main Authors: Skinner, Thomas E., Gershenzon, Naum I., Nimbalkar, Manoj, Glaser, Steffen J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-04-2012
• Subjects: Algorithms; Broadband; Excitation; Inhomogeneity; Magnetic Resonance Spectroscopy - methods; Magnetization; Optimal control; Optimal control theory; Performance enhancement; Radio frequencies; Radio Waves; RC-SEBOB; Relaxation; Selective excitation; Selectivity; Signal Processing, Computer-Assisted; T1 relaxation; T2 relaxation; Selective excitation; Relaxation; RC-SEBOB; Optimal control theory; T2 relaxation; T1 relaxation
• ISSN: 1090-7807; 1096-0856
• DOI: 10.1016/j.jmr.2012.02.007

Experimental selectivity profiles of eSNOB (left) and the relaxation-compensated optimal control pulse RC-SEBOP (right), pulse length Tp=1 ms, applied to a strongly relaxing sample with T1=1.345 ms and T2=1.024 ms. Results are shown for three values of the RF calibration relative to the ideal value B10 for each pulse, showing insensitivity of RC-SEBOP to RF miscalibration of ±10%. Passband signal gains of a factor of 2 are obtained with RC-BEBOP compared to eSNOB. [Display omitted]
► Relaxation-compensated selective excitation. ► Significant signal gains and improved selectivity profiles for fast-relaxing species. ► Insensitive to RF inhomogeneity/miscalibration of ±10%.
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-SEBOPs). We demonstrate simple pulse sequence elements for eliminating this unwanted residual signal.