Quantification of Oscillatory Shear Stress from Reciprocating CSF Motion on 4D Flow Imaging

Area of Science:

• Biomedical Engineering
• Fluid Dynamics
• Neurology

Background:

• Cerebrospinal fluid (CSF) flow is synchronized with heartbeat, creating oscillatory shear stress (OSS).
• Direct measurement of OSS, considering direction, was previously challenging.
• Idiopathic normal pressure hydrocephalus (iNPH) involves altered CSF dynamics.

Purpose of the Study:

• To evaluate the significance of OSS in the cerebral aqueduct and foramen magnum in iNPH.
• To compare OSS with wall shear stress (WSS) and oscillatory shear index (OSI) in iNPH patients.
• To investigate the relationship between OSS and CSF flow parameters.

Main Methods:

• 4D flow Magnetic Resonance Imaging (MRI) was used to measure OSS, WSS, and OSI.
• Measurements were taken in 41 iNPH patients, 23 with co-occurring Alzheimer's dementia, and 9 controls.
• Shear stress parameters were compared with Foramen of Magendie and cerebral aqueduct apertures and stroke volumes.

Main Results:

• OSS, reflecting directional WSS changes, was significantly higher in iNPH groups compared to controls, particularly at the cerebral aqueduct.
• Higher OSS at the cerebral aqueduct was observed in iNPH patients compared to those with co-occurring iNPH and Alzheimer's dementia.
• OSS amplitude correlated with Foramen of Magendie diameters and stroke volume at the cerebral aqueduct.

Conclusions:

• OSS is a direct, measurable parameter via 4D flow MRI that better represents WSS vector changes than WSS magnitude or OSI.
• Elevated OSS in the cerebral aqueduct is a significant finding in iNPH.
• OSS measurement offers a novel approach to understanding CSF dynamics in hydrocephalus.