Design of ramped RF excitation pulses with built-in out of slab saturation for 3D - TOF angiography

INTRODUCTION – In clinical practice, imaging of the intracranial arteries, such as the Circle of Willis (CoW), is performed most frequently with 3D TOF angiography. This noninvasive technique uses a T1-weighted RF-spoiled gradient echo (SPGR) sequence, typically in conjuction with multiple overlapping slabs (MOTSA) and RF slab excitation pulses with ramped excitation profile (TONE) to reduce blood saturation effects and to improve signal homogeneity of the vessel lumen. An additional proximal or distal SAT RF Pulse is usually added to explicitly eliminate arterial or venous blood signal, respectively. To achieve good blood saturation, the SAT band should be shifted with respect to each imaging slab and played out every TR with a corresponding gradient spoiler gradient to efficiently suppress even fast flowing blood. The addition of these additional SAT pulses, in turn, dramatically increases the scan time. Previous work by Cunningham et al. [1] showed that by concatenating a rectangle excitation profile with saturation bands on both sides can reduce scan time of triggered CE-MRA. A similar approach can be taken for TOF MRA. In this work, we leverage Shinnar-Le-Roux (SLR) transform to combine a minimum-phase small tip angle ramped excitation pulse with a onesided saturation band to either suppress the venous/or arterial signal in 3D TOF acquisitions.