Functional MRI of the human motor cortex using single-shot, multiple gradient-echo spiral imaging

Abstract

In this study, we combined the advantages of a fast multi-slice spiral imaging approach with a multiple gradient-echo sampling scheme at high magnetic field strength to improve quantification of BOLD and inflow effects and to estimate T ∗ 2 relaxation times in functional brain imaging. Eight echoes are collected with echo time (TE) ranging from 5 to 180 ms. Acquisition time per slice and echo time is 25 ms for a nominal resolution of 4 × 4 × 4 mm 3. Evaluation of parameter images during rest and stimulation yields no significant activation on the inflow sensitive spin-density images (ρ- or I 0-maps) whereas clear activation patterns in primary human motor cortex (M1) and supplementary motor area (SMA) are detected on BOLD sensitive T ∗ 2-maps. The calculation of relaxation times and rates of the activated areas over all subjects yields an average T ∗ 2 ± standard deviation (SD) of 46.1 ± 4.5 ms (R ∗ 2 of 21.8 ± 2.2 s −1) and an average increase (ΔT ∗ 2 ± SD) of 0.93 ± 0.47 ms (ΔR ∗ 2 of −0.4 ± 0.14 s −1). Our findings demonstrate the usefulness of a multiple gradient echo data acquisition approach in separating various vascular contributions to brain activation in fMRI.