Most Small Cerebral Cortical Veins Demonstrate Significant Flow Pulsatility: A Human Phase Contrast MRI Study at 7T

Abstract

Phase contrast MRI (pcMRI) has been used to investigate flow pulsatility in cerebral arteries, larger cerebral veins, and the cerebrospinal fluid (CSF). Such measurements of intracranial pulsatility and compliance are beginning to inform understanding of the pathophysiology of conditions including normal pressure hydrocephalus, multiple sclerosis, and dementias. We demonstrate the presence of flow pulsatility in small cerebral cortical veins, for the first time using pcMRI at 7 T, with the aim of improving our understanding of the hemodynamics of this little-studied vascular compartment. A method for establishing where venous flow is pulsatile is introduced, revealing significant pulsatility in 116 out of 146 veins, across eight healthy participants, assessed in parietal and frontal regions. Distributions of pulsatility index (PI) and pulse waveform delay were characterized, indicating a small, but statistically significant (p < 0.05), delay of 59 ± 41 ms in cortical veins with respect to the superior sagittal sinus, but no differences between veins draining different arterial supply territories. Measurements of pulsatility in smaller cortical veins, a hitherto unstudied compartment closer to the capillary bed, could lead to a better understanding of intracranial compliance and cerebrovascular (patho)physiology.

Assessment of single-vessel cerebral blood velocity by phase contrast fMRI

“…The T2*-weighted BOLD resting state fMRI signal fluctuation from individual vessels can be separated from noise artifacts due to pulsation or other motion effects. In contrast, pulsation could be a significant confounding issue for PC-based blood velocity mapping from individual vessels [ 61 , 62 ]. To better differentiate the pulsational contribution to CBFv signal fluctuation given different frequency ranges, we will need to increase the sampling rate by implementing phased-array surface coils for focal field of view measurement and an accelerated PC-MRI sequence.…”

Non‐Invasive Assessment of Damping of Blood Flow Velocity Pulsatility in Cerebral Arteries With MRI

“…This can result in severe motion artifacts and give unreliable velocity and pulsatility measurements. 39 This led to a considerable number of subjects to be excluded from small perforating artery analysis for the CSO level and BG level. This high exclusion rate is also known from earlier studies 7 , 9 and so far no quality assessment method has been developed to objectively exclude PC images from analysis.…”

A Print‐and‐Fuse Strategy for Sacrificial Filaments Enables Biomimetically Structured Perfusable Microvascular Networks with Functional Endothelium Inside 3D Hydrogels

“…[ 43 ] In smaller human cortical venules (below 20 µm), time‐averaged flow velocity was 0.5 cm s −1 in non‐pulsatile veins and 1.1 cm s −1 in pulsatile veins. [ 44 ] The average wall shear stress in different regions during each rocking half‐cycle was also significantly below the values reported for the small arteries and veins, [ 45 ] which is mainly associated with relatively slow perfusion velocities and also operation in atmospheric pressure. Despite these differences in flow velocities and wall shear stress, we noted the protective effect of perfusion on the ECs exposed to TNF‐α stimulation, both in 2D and 3D conditions.…”