BOLD fMRI at 9.4T with 3D stack-of-spirals readouts

To investigate the use of spiral readouts for sub-millimeter BOLD fMRI at 9.4T and to verify simulations of the BOLD point spread function (PSF) with functional experiments. Spiral readouts were evaluated through simulations and functional experiments to test their performance in sub-millimeter BOLD fMRI. Both spiral-out and spiral-in readout strategies were considered, with attention to echo time (TE) relative to T2*. We confirmed that a TE shorter than T2* can be employed for spiral-out readouts without compromising BOLD sensitivity. The use of shorter TE provided a reduced repetition time (TR), improved temporal signal-to-noise ratio (tSNR), and minimized off-resonance effects. Spiral-in readouts were found to be mainly useful for lower-resolution applications at ultra-high field (UHF). In contrast, segmented spiral-out readouts demonstrated strong potential for mesoscopic BOLD fMRI at ultra-high fields (> 7T).