Molly Gallogly Bright1, 2, Marta Bianciardi2, 3, Jacco A. de Zwart2, Jeff H. Duyn2
1CUBRIC, School of Psychology, Cardiff University, Cardiff, United Kingdom; 2Advanced MRI Section, LFMI, NINDS, National Institutes of Health, Bethesda, MD, United States; 3A.A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States
Negative fMRI signal changes have been observed in large cerebral vessels, and modeling suggests this phenomenon originates from changes in blood volume rather than deoxyhemoglobin concentration. To better understand the underlying mechanisms, respiratory challenges were used to create transient hypocapnia and global decreases in blood volume in 10 subjects during BOLD-weighted EPI acquisition at 7 Tesla. The global timeseries was correlated with every voxel, and the time-to-peak of the voxelwise response was extracted. Large vessels exhibited anticorrelated signal changes of physiological origin that occurred significantly earlier than the response across gray matter, suggesting early blood volume changes are responsible.