Trading off spatio‐temporal properties in 3D high‐speed fMRI using interleaved stack‐of‐spirals trajectories

Purpose Highly undersampled acquisitions have been proposed to push the limits of temporal resolution in functional MRI. This contribution is aimed at identifying parameter sets that let the user trade‐off between ultra‐high temporal resolution and spatial signal quality by varying the sampling densities. The proposed method maintains the synergies of a temporal resolution that enables direct filtering of physiological artifacts for highest statistical power, and 3D read‐outs with optimal use of encoding capabilities of multi‐coil arrays for efficient sampling and high signal‐to‐noise ratio (SNR). Methods One‐ to four‐shot interleaved spherical stack‐of‐spiral trajectories with repetition times from 96 to 352 ms at a nominal resolution of 3 mm using different sampling densities were compared for image quality and temporal SNR (tSNR). The one‐ and three‐shot trajectories were employed in a resting state study for functional characterization. Results Compared to a previously described single‐shot trajectory, denser sampled trajectories of the same type are shown to be less prone to blurring and off‐resonance vulnerability that appear in addition to the variable density artifacts of the point spread function. While the multi‐shot trajectories lead to a decrease in tSNR efficiency, the high SNR due to the 3D read‐out, combined with notable increases in image quality, leads to superior overall results of the three‐shot interleaved stack of spirals. A resting state analysis of 15 subjects shows significantly improved functional sensitivity in areas of high off‐resonance gradients. Conclusion Mild variable‐density sampling leads to excellent tSNR behavior and no increased off‐resonance vulnerability, and is suggested unless maximum temporal resolution is sought.