Inflow effect in functional MRI using gradient-echo at 1.5 T

Abstract

On functional MRI (fMRI) the main reason for signal changes is thought to depend on the blood oxygenation level dependent (BOLD) contrast. On fMRI, using the conventional GFE T2* effect, it appears to be mixed with significant blood flow (inflow) signal due to the large flip angle and short TR of the GFE technique. We attempted to discriminate between the susceptibility effects and the inflow effects with presaturation (SAT) methods. A series of 15 sequential images was acquired with a long TE GFE sequence under photic stimulation. We inserted the SAT slab above and below the imaging plane to suppress the unsaturated flowing protons. To alter the inflow effects, we changed the distance between the imaging plane and the SAT slab. When the distance was increased, the quantity of signal intensity changes had also increased, and the signal changes were observed even when the imaging plane and the SAT slab were adjacent. Our results show that the signal changes on fMRI with conventional GFE technique are affected by inflow effects and BOLD contrast.