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Abstract #1547

Arterial Contribution to the BOLD fMRI Response to Somatosensory Stimulation in Rats

Yoshiyuki Hirano1, Afonso C. Silva2

1Cerebral Microcirculation Unit, Laboratory of Functional & Molecular Imaging, National Institute of Neurological Disorders & Stroke, National Institutes of Health, Bethesda, MD, United States; 2Cerebral Microcirculation Unit, Laboratory of Functional & Molecular Imaging,, National Institute of Neurological Disorders & Stroke, National Institutes of Health, Bethesda, MD, United States


Biophysical models of BOLD contrast assume that the arterial vasculature is fully saturated with oxygen, so that BOLD originates in capillaries and veins. Here, we measured the BOLD and CBF fMRI response to somatosensory stimulation in α-chloralose anesthetized rats under different levels of arterial oxygenation. The CBF response was not affected by arterial oxygenation, while the onset time of the BOLD response in hypoxia was significantly longer than those in normoxia or hyperoxia. The onset time difference between BOLD-CBF was significantly smaller than the arteriole-venule transit time, suggesting that a measurable fraction of the BOLD response is of arterial origin.