Comparison of BOLD and perfusion based event-related functional MRI

Functional MRI (fMRI) utilizing both perfusion and blood oxygenation level-dependent (BOLD) contrast has been extensively used in human brain mapping. In most cases, techniques based on both contrasts have been performed using a blocked task paradigm. Most recently, both perfusion and BOLD based event-related fMRI (ER-fMRI) were developed to study the transient hemodynamic response to a short stimulus. A direct comparison of these two ER-fMRI techniques will improve our understanding of the hemodynamic response due to brain activation. In this study, we compare the temporal response in perfusion and BOLD based ER-fMRI. Experiments were performed on a 1.9 T GE/Elscint Prestige MRI scanner, on 6 healthy human subjects. For perfusion based imaging, a flow-sensitive alternating inversion recovery (FAIR) EPI technique was used, with a temporal resolution of 1 s. For the BOLD based imaging, a T₂*-weighted gradient-echo EPI was used with the same temporal resolution. A checkerboard flashing at 8 Hz was presented as the short visual stimulus (1 s). Ten trials were averaged. Percent maximum change, time-to-peak (TTP) and FWHM of the responses were determined on the activated voxels (p<0.05). FAIR signal changes (18.4 ± 1.6%) are much higher than BOLD signal changes (1.0 ± 0.1%). The mean TTP occurs 0.9 s earlier for perfusion than BOLD (4.2 ± 0.2 s vs. 5.1 ± 0.2 s, p < 0.05). No significant difference was observed between the FWHM of the perfusion (5.1 ± 0.6 s) and which of the BOLD responses (5.9 ± 0.6 s). A positive linear correlation was found between the maximum perfusion and maximum BOLD signal changes (r = 0.77).