Figure 1 illustrates the acquisition challenges in layer-dependent fMRI. For large coverage protocols, it can be beneficial to interleave the contrast generation periods with readout periods. In MAGEC VASO (Fig. 1A), the CBV-weighting is introduced between every 3D-EPI readout block instead of a sole single inversion pulse. This allows an increase of the acquisition window and, thus enables more slices to be acquired. Similarly, for in-plane segmented readout strategies, multiple contrast-generating inversion pulses are applied per image. One of the most critical and most investigated challenges of layer-fMRI acquisition is the unwanted vascular bias of large draining veins. Fig. 1B conceptualizes the corresponding localization specificity in conventional GE-BOLD and blood volume sensitive VASO. It can be seen that VASO has a higher localization specificity, without strong signal leakage effects of large pial veins. However, it has a lower detection threshold with fewer significantly activated voxels. Two stripes of layer-dependent activity are visible in VASO, representing the input and output activity of layers II/III and layer Vb/VI, respectively.
