Large Influence of Flow-Related Contribution on FMRI Signal: A 9.4T Study Using Hypercapnia

Xiao Wang¹, Xiao hong Zhu¹, Yi Zhang¹, Wei Chen¹

Although fMRI based on BOLD contrast has become one most prominent neuroimaging modality for mapping brain activity, it is still elusive whether the measured signal by fMRI is completely originated from the true BOLD or could be significantly contributed by the flow-related component, and if yes, whether the flow-related component is from macro- or micro vascular origin. The primary goals of this study are: i) to quantitatively investigate the relative contributions from BOLD and flow-related signal in the rat brain cortex at 9.4T using hypercapnia. The results indicate that: i) the flow-related contribution into the total signal change detected by fMRI is large and compatible to the BOLD contribution when a short repetition time is applied; and ii) the flow-related signal is mainly originated from perfusion change and inflow effect in small arterioles, thus, it can be utilized to further improve sensitivity and specificity of fMRI for mapping neuronal activity during brain activation.