Optimization of adiabatic pulses for pulsed arterial spin labeling at 7 tesla: Comparison with pseudo-continuous arterial spin labeling

Purpose: To optimize and evaluate adiabatic pulses for pulsed arterial spin labeling at ultrahigh field 7 tesla. Methods: Four common adiabatic inversion pulses, including hyperbolic secant, wideband uniform rate smooth truncation, frequency offset corrected inversion, and time-resampled frequency offset corrected inversion pulses, were optimized based on a custom-defined loss function that included labeling efficiency and inversion band uniformity. The optimized pulses were implemented in flow-sensitive alternating inversion recovery sequences and tested on phantom and 11 healthy volunteers with 2 constraints: 1) specific absorption rate normalized; and 2) equal peak RF amplitude, respectively. A pseudo-continuous arterial spin labeling sequence was implemented for comparison. Quantitative metrics such as perfusion and relative labeling efficiency versus residual tissue signal were calculated. Results: Among the 4 pulses, the wideband uniform rate smooth truncation pulse yielded the lowest loss in simulation and achieved a good balance between labeling efficiency and residual tissue signal from both phantom and in vivo experiments. Wideband uniform rate smooth truncation-pulsed arterial spin labeling showed significantly higher relative labeling efficiency compared to the other sequences (P < .01), whereas the perfusion signal was increased by 40% when the highest B1+ amplitude was used. The 4 pulsed arterial spin labeling sequences yielded comparable perfusion signals compared to pseudo-continuous arterial spin labeling but with less than half the specific absorption rate. Conclusion: Optimized wideband uniform rate smooth truncation pulse with the highest B1+ amplitude allowed was recommended for 7 tesla pulsed arterial spin labeling.

Automated summary

The purpose of this study was to optimize and evaluate adiabatic pulses for pulsed arterial spin labeling at ultra-high field 7 Tesla. Among the four pulses examined, the wideband uniform rate smooth truncation pulse achieved the best balance between labeling efficiency and residual tissue signal, showing significantly higher relative labeling efficiency compared to other sequences. The optimized pulse allowed for comparable perfusion signals as pseudo-continuous arterial spin labeling but with less than half the specific absorption rate.