High resolution SE-fMRI in humans at 3 and 7 T using a motor task

Object The sensitivity of spin echo (SE) experiments to blood oxygenation level dependent (BOLD) contrast was explored in a study of the same six subjects carried out at 3 and 7 T. Materials and methods Multi-slice, single shot, spin echo, echo planar images with a voxel size of 1 × 1 × 3 mm³ were acquired at three different echo times, during execution of a simple motor task. Results Significant activation was observed at all echo times at both field strengths. Analysis of the fractional signal change as a function of echo time indicated that the change in relaxation rate, ΔR ₂, at 7 T was −0.51 ± 0.14 s ⁻¹, which was 1.3 times larger than the value found at 3 T. Measurements of the percentage signal change on activation and temporal signal to noise ratio showed that there was an increase in the BOLD contrast to noise ratio (CNR) at 7 versus 3 T by a factor of 1.9. There was no overlap of areas of significant activation in the SE data acquired at either field strength with the site of large veins. Conclusion SE-BOLD CNR in motor cortex was found to increase significantly at 7 T compared with 3 T.