Non-invasive measurement of choroid plexus apparent blood flow with arterial spin labeling

Abstract

Background The choroid plexus is a major contributor to the generation of cerebrospinal fluid (CSF) and the maintenance of its electrolyte and metabolite balance. Here, we sought to characterize the blood flow dynamics of the choroid plexus using arterial spin labeling (ASL) MRI to establish ASL as a non-invasive tool for choroid plexus function and disease studies. Methods Seven healthy volunteers were imaged on a 3T MR scanner. ASL images were acquired with 12 labeling durations and post labeling delays. Regions of the choroid plexus were manually segmented on high-resolution T1 weighted images. Choroid plexus perfusion was characterized with a dynamic ASL perfusion model. Cerebral gray matter perfusion was also quantified for comparison. Results Kinetics of the ASL signal were clearly different in the choroid plexus than in gray matter. The choroid plexus has a significantly longer T1 than the gray matter (2.33 ± 0.30 s vs. 1.85 ± 0.10 s, p < 0.02). The arterial transit time was 1.24 ± 0.20 s at the choroid plexus. The apparent blood flow to the choroid plexus was measured to be 39.5 ± 10.1 ml/100 g/min and 0.80 ± 0.31 ml/min integrated over the posterior lateral ventricles in both hemispheres. Correction with the choroid plexus weight yielded a blood flow of 80 ml/100 g/min. Conclusions Our findings suggest that ASL can provide a clinically feasible option to quantify the dynamic characteristics of choroid plexus blood flow. It also provides useful reference values of the choroid plexus perfusion. The long T1 of the choroid plexus may suggest the transport of water from arterial blood to the CSF, potentially providing a method to quantify CSF generation.

Choroid plexus perfusion in sickle cell disease and moyamoya vasculopathy: Implications for glymphatic flow

“…A similar protocol has recently been applied in healthy adults and has demonstrated that arterial arrival to the CP is 1.24 AE 0.2 s, T 1 of the CP is 2.33 AE 0.30 s, and apparent CP perfusion is 39.5 ml/100 g/min. 27 Our perfusion values from this study and our previous study 4 are in good agreement with this perfusion value. It should be noted that arrival time and T 1 of the CP is longer than for cortex.…”

“…It should also be noted that as the CP is a relatively small structure, partial volume effects with CSF or periventricular tissue may also affect measurements and lead to an underestimation of true CP perfusion. 27 To reduce this concern we segmented the CP manually on T 1 -weighted images, however, given the inherent lower spatial resolution of pCASL some partial volume contributions will persist, but are expected to be similar in all participants. The extent of atrophy, and associated size of the lateral ventricles, may influence the ability to accurately segment the CP and as such the measured CP perfusion.…”

“…The shorter labeling duration of 1000 ms for Protocol-2 was used here as the pCASL scan was also part of a broader multi-post-labeling delay protocol to quantify blood arrival time in SCD, and the shorter label duration was required to sensitize the sequence to blood arrival at short post-labeling delays. Note that the post-labeling delay times utilized here are much longer, as required, than the arterial transit time of blood to the CP, recently measured to be 1.24 AE 0.20 s. 27 This comparative analysis was performed as the pCASL protocol applied to moyamoya (Protocol-1) and SCD (Protocol-2) differed owing to known reductions in bolus arrival time in SCD compared to moyamoya and additional transit time considerations noted above. 22,30 The difference in parameter choice was also motivated by previous studies demonstrating that blood arrival times are reduced in healthy 31 and SCD 30 adults relative to adults with moyamoya, 22,32 and the desire to titrate the sequence appropriately to each population.…”

“…We also explore a secondary hypothesis that CP perfusion is elevated in adults with moyamoya vasculopathy and reduced arterial patency and cortical perfusion. These hypotheses are motivated by earlier animal studies of manipulated arterial pulsatility 13 and recent work applying ASL to measure CP blood arrival 27 and perfusion. 4,27 If confirmed, findings would provide additional support for glymphatic flow in humans, and specifically that CP activity is related to cortical perfusion and the compliance of perivascular pathways.…”

Brain Barriers and brain fluids research in 2020 and the fluids and barriers of the CNS thematic series on advances in in vitro modeling of the blood–brain barrier and neurovascular unit

“…Evans et al [49] recently described using magnetic resonance imaging (MRI) to measure the movement of water from arterial blood to CSF in human brain as well as mouse. MRI was also used by Zhao et al [50] to examine CP hemodynamic parameters (flow, transit time) in humans. Eide et al [51] used MRI to track the clearance of gadobutrol after intrathecal administration in healthy individuals and those with idiopathic normal pressure hydrocephalus.…”