1Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, United States; 2Department of Bioengineering, University of Texas Southwestern Medical Center/University of Texas at Arlington, Arlington, TX, United States; 3Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX, United States; 4Department of Radiology, Leiden University Medical Center, Leiden, ZA, Netherlands
Cerebral vascular reactivity (CVR), measured by combining BOLD MRI and hypercapnia, could be a promising biomarker for small vessel disease. However, the mechanism of BOLD change during CO2 challenge has not been fully understood. In this study we report an intriguing but robust observation of negative CVR (i.e. BOLD signal decreased during CO2 inhalation) in brain ventricles. We further showed this BOLD signal reduction can be attributed to CSF space shrinkage due to ventricular vessel dilation, but not due to T2* reduction. We also show the negative CVR is not present during O2 challenge, known to cause minimal vessel dilation.