Figure 2.

Sequences assayed for the Hybrid SPEN/k-space pMRI experiments. (a) Single-slice version based on a 90° multi-band pulse encoding simultaneously adjacent spatial regions; slice selection is done by the sinc180° pulse (b) Multi-slice hybrid SPEN/k-space pMRI sequence using a multi-band adiabatic 180 inversion pulse to simultaneously encode adjacent spatial regions; a final 180° hard pulse serves to return all the magnetization that was not addressed by the initial 90° slice-selective pulse, back to the +z axis. The RF/ADC line displays both the pulses and the timing of the acquisitions (ADC for Analogue-to-Digital Converter); G_RO, G_SPEN and G_SS rows display respectively the gradients applied along the readout, the spatiotemporally-encoded and the slice-selective directions. The parameters of the scans are as described in previous SPEN implementations [14. 20]; their novelty lies in the replacement of the 90° and 180° swept pulses by multi-band swept analogues, and the concomitant reduction of the encoding and acquisition times by a factor equal to the number of employed bands. Main experimental parameters are: T_acq, G_acq –acquisition duration and gradient strength associated to the slow SPEN dimensions; T_ro, G_ro – acquisition duration and gradient strength associated with the orthogonal k-space readout dimension; N_slices, N_lines –number of slice-selective and of SPEN-decoded elements; T_exc, G_exc, T₁₈₀, G₁₈₀ –chirp pulse duration and associated gradient strength in (a) and in (b), respectively; k_ro and k_SPEN– pairs of prewinding gradients flanking the adiabatic 180° inversion and imparting ≈ϒG_roT_ro/2 and ≈ϒG₁₈₀T₁₈₀ encodings respectively; G_cr and G_sp –crusher and spoiler gradients applied on all axes.