Reducing Contamination in PASL using BASSI RF pulses

Introduction Arterial spin labeling is sensitive to contamination due to off-resonance effects of the RF label. While it has been argued that in PASL these effects are small compared to pulse profile effects [1], this assessment has to be re-evaluated in view of the advent of highly selective gradient-modulated adiabatic pulses such as FOCI [2], requiring several times more RF energy than the classic hyperbolic secant (HS) RF pulses. BASSI (Bandwidth Modulated Adiabatic Selective Saturation and Inversion) pulses are a class of frequencyand gradient-modulated RF pulses, derived from the hyperbolic secant pulse by temporal variation of the bandwidth parameter [3,4]. These pulses achieve uniform and highly selective profiles at any effective flip angle, while reducing RF energy significantly compared to FOCI pulses of similar performance. Here we present our work on optimizing BASSI RF pulses for use in PASL and evaluate their performance in terms of off-resonance contamination detectable in in vivo perfusion images.