Pseudo-continuous transfer insensitive labeling technique.

Transfer insensitive labeling technique (TILT) was previously applied to acquire multislice cerebral blood flow maps as a pulsed arterial spin labeling (PASL) method. The magnetization transfer effect with TILT is well controlled by using concatenated radiofrequency pulses. However, use of TILT has been limited by several challenges, including slice profile errors, sensitivity to arterial transit time and intrinsic low signal-to-noise ratio (SNR). In this work, we propose to address these challenges by making the original TILT method into a novel pseudo-continuous arterial spin labeling approach, named pseudo-continuous transfer insensitive labeling technique (pTILT). pTILT improves perfusion acquisitions by (i) realizing pseudo-continuous tagging with nonadiabatic pulses, (ii) being sensitive to slow flows in addition to fast flows, and (iii) providing flexible labeling geometries. Perfusion maps during both resting state and functional tasks are successfully demonstrated in healthy volunteers with pTILT. A comparison with typical SNR values from other perfusion techniques shows that although pTILT provides less SNR than inversion-based pseudo-continuous ASL techniques, the modified sequence provides similar SNR to inversion-based PASL techniques.