Sensitivity of BOLD response to increasing visual contrast: Spin echo versus gradient echo EPI

摘要: Previous evidence showed that spin-echo (SE) BOLD signals offer an increased linearity and promptness with respect to gradient-echo (GE) acquisition, possibly providing a more accurate estimate of the amplitude neuronal activity. However there is no two sequences differ in representing different activation levels due changes stimulus intensity. In this study at 3T we compared GE SE responses visual stimuli increasing contrast (5%, 20%, 60%, 100%). Both monotonic increase response contrast. While larger sensitivity yielded overall signal changes, step-wise for was significant only when comparing 20% 5% contrast, whereas observed also 60% Moreover, normalized lowest relative increases fMRI strength are corresponding values signal. This difference excluding voxels attributed large vessels, suggesting non negligible role extravascular contribution modulation These results shown be agreement theoretical predictions derived from recently proposed model functional signals. The present findings suggest that, despite limited localization accuracy low field, might potential advantage distinguishing stimulus-evoked brain