Browsing by Author "Wright, Adam M."

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    Coupled pulsatile vascular and paravascular fluid dynamics in the human brain
    (Springer Nature, 2024-09-11) Wright, Adam M.; Wu, Yu‑Chien; Yang, Ho‑Ching; Risacher, Shannon L.; Saykin, Andrew J.; Tong, Yunjie; Wen, Qiuting; Radiology and Imaging Sciences, School of Medicine
    Background: Cardiac pulsation propels blood through the cerebrovascular network to maintain cerebral homeostasis. The cerebrovascular network is uniquely surrounded by paravascular cerebrospinal fluid (pCSF), which plays a crucial role in waste removal, and its flow is suspected to be driven by arterial pulsations. Despite its importance, the relationship between vascular and paravascular fluid dynamics throughout the cardiac cycle remains poorly understood in humans. Methods: In this study, we developed a non-invasive neuroimaging approach to investigate the coupling between pulsatile vascular and pCSF dynamics within the subarachnoid space of the human brain. Resting-state functional MRI (fMRI) and dynamic diffusion-weighted imaging (dynDWI) were retrospectively cardiac-aligned to represent cerebral hemodynamics and pCSF motion, respectively. We measured the time between peaks (∆TTP) in d d ϕ f M R I and dynDWI waveforms and measured their coupling by calculating the waveforms correlation after peak alignment (correlation at aligned peaks). We compared the ∆TTP and correlation at aligned peaks between younger [mean age: 27.9 (3.3) years, n = 9] and older adults [mean age: 70.5 (6.6) years, n = 20], and assessed their reproducibility within subjects and across different imaging protocols. Results: Hemodynamic changes consistently precede pCSF motion. ∆TTP was significantly shorter in younger adults compared to older adults (-0.015 vs. -0.069, p < 0.05). The correlation at aligned peaks were high and did not differ between younger and older adults (0.833 vs. 0.776, p = 0.153). The ∆TTP and correlation at aligned peaks were robust across fMRI protocols (∆TTP: -0.15 vs. -0.053, p = 0.239; correlation at aligned peaks: 0.813 vs. 0.812, p = 0.985) and demonstrated good to excellent within-subject reproducibility (∆TTP: intraclass correlation coefficient = 0.36; correlation at aligned peaks: intraclass correlation coefficient = 0.89). Conclusion: This study proposes a non-invasive technique to evaluate vascular and paravascular fluid dynamics. Our findings reveal a consistent and robust cardiac pulsation-driven coupling between cerebral hemodynamics and pCSF dynamics in both younger and older adults.
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    Diffusion magnetic resonance imaging of cerebrospinal fluid dynamics: Current techniques and future advancements
    (Wiley, 2024) Wright, Adam M.; Wu, Yu-Chien; Feng, Li; Wen, Qiuting; Radiology and Imaging Sciences, School of Medicine
    Cerebrospinal fluid (CSF) plays a critical role in metabolic waste clearance from the brain, requiring its circulation throughout various brain pathways, including the ventricular system, subarachnoid spaces, para-arterial spaces, interstitial spaces, and para-venous spaces. The complexity of CSF circulation has posed a challenge in obtaining noninvasive measurements of CSF dynamics. The assessment of CSF dynamics throughout its various circulatory pathways is possible using diffusion magnetic resonance imaging (MRI) with optimized sensitivity to incoherent water movement across the brain. This review presents an overview of both established and emerging diffusion MRI techniques designed to measure CSF dynamics and their potential clinical applications. The discussion offers insights into the optimization of diffusion MRI acquisition parameters to enhance the sensitivity and specificity of diffusion metrics on underlying CSF dynamics. Lastly, we emphasize the importance of cautious interpretations of diffusion-based imaging, especially when differentiating between tissue- and fluid-related changes or elucidating structural versus functional alterations.
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    Dynamic diffusion-weighted imaging of intracranial cardiac impulse propagation along arteries to arterioles in the aging brain
    (Sage, 2025-02-13) Wen, Qiuting; Muskat, Joseph; Babbs, Charles F.; Wright, Adam M.; Zhao, Yi; Zhou, Xiaopeng; Zhu, Chengcheng; Tong, Yunjie; Wu, Yu-Chien; Risacher, Shannon L.; Saykin, Andrew J.; Radiology and Imaging Sciences, School of Medicine
    Intracranial cardiac impulse propagation along penetrating arterioles is vital for both nutrient supply via blood circulation and waste clearance via CSF circulation. However, current neuroimaging methods are limited to simultaneously detecting impulse propagation at pial arteries, arterioles, and between them. We hypothesized that this propagation could be detected via paravascular CSF dynamics and that it may change with aging. Using dynamic diffusion-weighted imaging (dynDWI), we detected oscillatory CSF motion synchronized with the finger photoplethysmography in the subarachnoid space (SAS) and cerebral cortex, with a delay revealing an impulse propagation pathway from the SAS to the cortex, averaging 84 milliseconds. Data from 70 subjects aged 18 to 85 years showed a bimodal age-related change in the SAS-Cortex travel time: it initially increases with age, peaks around 45 years, then decreases. Computational biomechanical modeling of the cardiovascular system was performed and replicated this 84-millisecond delay. Sensitivity analysis suggests that age-related variations in travel time are primarily driven by changes in arteriolar compliance. These findings support the use of dynDWI for measuring intracranial impulse propagation and highlight its potential in assessing related vascular and waste clearance functions.
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    Human CSF movement influenced by vascular low frequency oscillations and respiration
    (Frontiers Media, 2022-08-19) Nair, Vidhya Vijayakrishnan; Kish, Brianna R.; Inglis, Ben; Yang, Ho-Ching (Shawn); Wright, Adam M.; Wu, Yu-Chien; Zhou, Xiaopeng; Schwichtenberg, Amy J.; Tong, Yunjie; Radiology and Imaging Sciences, School of Medicine
    Cerebrospinal fluid (CSF) movement through the pathways within the central nervous system is of high significance for maintaining normal brain health and function. Low frequency hemodynamics and respiration have been shown to drive CSF in humans independently. Here, we hypothesize that CSF movement may be driven simultaneously (and in synchrony) by both mechanisms and study their independent and coupled effects on CSF movement using novel neck fMRI scans. Caudad CSF movement at the fourth ventricle and hemodynamics of the major neck blood vessels (internal carotid arteries and internal jugular veins) was measured from 11 young, healthy volunteers using novel neck fMRI scans with simultaneous measurement of respiration. Two distinct models of CSF movement (1. Low-frequency hemodynamics and 2. Respiration) and possible coupling between them were investigated. We show that the dynamics of brain fluids can be assessed from the neck by studying the interrelationships between major neck blood vessels and the CSF movement in the fourth ventricle. We also demonstrate that there exists a cross-frequency coupling between these two separable mechanisms. The human CSF system can respond to multiple coupled physiological forces at the same time. This information may help inform the pathological mechanisms behind CSF movement-related disorders.
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    Robust data-driven segmentation of pulsatile cerebral vessels using functional magnetic resonance imaging
    (Royal Society, 2024-12-06) Wright, Adam M.; Xu, Tianyin; Ingram, Jacob; Koo, John; Zhao, Yi; Tong, Yunjie; Wen, Qiuting; Radiology and Imaging Sciences, School of Medicine
    Functional magnetic resonance imaging (fMRI) captures rich physiological and neuronal information, offering insight into neurofluid dynamics, vascular health and waste clearance. Accurate cerebral vessel segmentation could greatly facilitate fluid dynamics research in fMRI. However, existing vessel identification methods, such as magnetic resonance angiography or deep-learning-based segmentation on structural MRI, cannot reliably locate cerebral vessels in fMRI space due to misregistration from inherent fMRI distortions. To address this challenge, we developed a data-driven, automatic segmentation of cerebral vessels directly within fMRI space. This approach identified large cerebral arteries and the superior sagittal sinus (SSS) by leveraging these vessels' distinct pulsatile signal patterns during the cardiac cycle. The method was validated in a local dataset by comparing it to ground truth cerebral artery and SSS segmentations. Using the Human Connectome Project (HCP) ageing dataset, the method's reproducibility was tested on 422 participants aged 36-90, each with four repeated fMRI scans. The method demonstrated high reproducibility, with an intraclass correlation coefficient > 0.7 in both cerebral artery and SSS segmentation volumes. This study demonstrates that large cerebral arteries and SSS can be reproducibly and automatically segmented in fMRI datasets, facilitating reliable fluid dynamics investigation in these regions.