The primary aim of the project “Go with the flow: the heart-brain axis” was to elucidate the interaction between heart and the brain, across the lifespan. This was done by integration of... Show moreThe primary aim of the project “Go with the flow: the heart-brain axis” was to elucidate the interaction between heart and the brain, across the lifespan. This was done by integration of physiological concepts into the MRI-environment and by monitoring brain perfusion at both the macrovascular level (using transcranial Doppler; TCD) and the tissue level (using arterial spin labeling MRI; ASL). This thesis focused on the comparison and validation of these two modalities used in this project. We found that high levels of end-tidal CO2, blood pressure and handgrip all influence the middle cerebral artery (MCA) diameter, challenging the long-held assumption of diameter constancy. Furthermore, we found that during rhythmic handgrip the flow velocity (TCD) increased, whereas no change in the MCA flow territory (ASL) could be observed. Therefore, whole-brain CBF-measurements by ASL do not support the claim that a change in flow velocity measured by TCD can be used as a proxy for regional CBF during rhythmic handgrip exercise. Finally, we found in simulations and in-vivo experiments only modest influence of the cardiac cycle on the end-of-labeling. Therefore, cardiac triggering at the start or the end of labeling has little benefit to pseudo-Continuous ASL signal stability. Show less
