Fig. 1. Magnetization preparation, readout, and sequence timing.

Schematic depiction of one TR in the SS-SI-VASO sequence. (A) and (B) show the timing of the most relevant RF and gradient events for 2D-SMS and 3D-segmented-EPI, respectively. Zoomed views of the corresponding readout modules for individual slices and k-space segments are depicted in (D)–(E). Every TR starts with a ‘global’ adiabatic inversion pulse. A phase skip is used to control the inversion efficiency and the inflow of fast, un-inverted blood. The VASO images are acquired around the blood-nulling time at TI₁ = 1.1 s after successive application of the multi-band/slab-selective RF excitation pulses for 2D-SMS and 3D acquisitions, respectively. The multi-band factor varies between 1 and 3 in this study (SMS-factor = 3 in (D)). The phase-encoding and read gradients for the acquisition of the individual slices or k-space segments are accompanied with blipped-CAIPI gradients in slice/segment-direction for controlled aliasing of nearby slices. In this study the corresponding FOV-shift factor varied between 1 and 1/3 (FoV-shift = 1/2 in (D)–(E)). A second set of images is acquired at TI₂ = 2.6 s containing BOLD-signal-weighting without CBV-weighting. Example brain volumes from every readout are depicted next to their RF and gradient events. Since, the effective TI can vary across slices in the 2D-SMS approach in the range of 200 ms, clear borders of the individual SMS slabs can be seen from the corresponding steps in T₁-weighting (blue arrows in (A)).