3D single-shot VASO using a Maxwell gradient compensated GRASE sequence.

The vascular space occupancy (VASO) method was recently proposed as a functional MRI (fMRI) method that is capable of detecting activation-related changes in blood volume (CBV), without the need for a blood-pool contrast agent. In the present work we introduce a new whole-brain VASO technique that is based on a parallel-accelerated single-shot 3D GRASE (gradient and spin echo) readout. The GRASE VASO sequence employs a flow-compensated correction scheme for concomitant Maxwell gradients which is necessary to avoid smearing artifacts that may occur due to violation of the Carr-Purcell-Meiboom-Gill (CPMG) condition for off-resonance excitation. Experiments with 6 min of visual-motor stimulation were performed on eight subjects. At P < 0.01, average percent signal change and t-score for visual stimulation were -3.11% and -8.42, respectively; activation in left and right motor cortices and supplementary motor area was detected with -2.75% and -6.70, respectively. Sensitivity and signal changes are comparable to those of echo-planar imaging (EPI)-based single-slice VASO, as indicated by additional visual-task experiments (-3.39% and -6.93). The method makes it possible to perform whole-brain cognitive activation studies based on CBV contrast.