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Fluid-structure Interaction in Brain Dynamics

Thorough understanding of the cerebrospinal fluid dynamics and its complex interaction with the brain tissues is an important step in understanding the causes of different abnormalities in the central nervous system and designing potential remedies.

In this News, we present a study of the dynamics of the cerebrospinal fluid (CSF) and its interactions with the brain tissues using ADINA FSI, which offers some explanations for the potential causes of hydrocephalus (see Ref.).

The schematic of the problems is shown in Figure 1. The cerebrospinal fluid flows through the ventricles, the cerebral and spinal subarachnoid spaces (SAS), and the porous parenchyma in a pulsatile manner. The dynamics of the blood and cerebrospinal fluid flows result in deformations of the brain tissues. The aim of this study is to use an anatomically accurate coupled fluid structure system to study the cerebrospinal fluid dynamics.

MRI scan images of normal and hydrocephalic subjects are used for constructing the patient-specific model geometries and anatomically accurate poroelastic finite element models. Each finite element model includes the cerebrospinal fluid, the brain parenchyma and the spinal canal (Figure 2).




Figure 1 Schematic of different parts of the brain



Figure 2 Finite element model of cranio-spinal system for normal and communicating hydrocephalus subjects


The cerebrospinal fluid is assumed to be an incompressible, viscous Newtonian fluid. The parenchyma and the spinal cord are modeled as saturated poroelastic media (Figure 2). Prescribed displacement boundary conditions emulate the expansion and dilation of the cerebral vasculature occurring during the cardiac cycle. This in turn results in pulsatile cerebrospinal fluid flow.

The cerebrospinal fluid velocity and pressure fields throughout the cranio-spinal system were calculated by solving the Navier-Stokes and Darcy flow equations coupled with the equations of motion of the solid, the brain tissues.

The animations above show the variation of the cerebrospinal fluid velocity and pressure fields throughout the cranio-spinal system during the cardiac cycle.

Figure 3 compares the cerebrospinal fluid flow pattern between a normal (left) and a hydrocephalic subject (right). As seen, the location and magnitude of maximum velocity changes due to hydrocephalus.




Figure 3 Comparison of cerebrospinal fluid flow pattern between normal (left) and hydrocephalic (right) subjects


Figure 4 depicts the pressure field throughout the ventricular system and the subarachnoid spaces when the transmantle pressure gradient is maximum. As seen, the maximum pressure in the hydrocephalus case is more than 5 times greater than that of the normal subject.




Figure 4 Comparison between the intercranial pressure of normal subject and hydrocephalic patient


Figure 5 shows the stress distribution in the cerebrum and the cerebrospinal fluid flow patterns. As seen, cerebrospinal fluid flows throughout the ventricular system as well as seeps through the cerebrum. The cerebrospinal fluid is constantly produced in the ventricles and reabsorbed through the sagittal sinus.




Figure 5 Stress distribution and flow pattern for a communicating hydrocephalus patient




Figure 6 Comparison between the computational results and the in vivo cerebrospinal fluid flow measurements


Figure 6 depicts the variation of the cerebrospinal fluid velocity at a particular spatial location during the cardiac cycle for normal and hydrocephalus subjects. As seen, the computed velocities reasonably agree with the in vivo CINE-MRI cerebrospinal fluid measurements.

For further results, see the following videos:

Cerebrospinal fluid
pressure field
       Cerebrospinal fluid
velocity magnitudes
       Cerebrospinal fluid
velocity vector field

This study presents one of the many applications of ADINA FSI in biomechanics. ADINA provides the state of the art analysis capability for modeling complicated biomechanical problems. For other applications, see our ADINA FSI Publications and also our page on Biomechanical Applications of ADINA.

 

Reference

  • A.A. Linninger, B. Sweetman, R. Penn, "Normal and hydrocephalic brain dynamics: the role of reduced cerebrospinal fluid reabsorption and ventricular enlargement", Annals of Biomedical Engineering, Vol. 73, pp. 1434-1447, 2009


Keywords:
cerebrospinal dynamics, hydrocephalus, biomechanics, fluid structure interaction, FSI, porous media, brain, MRI, Intracranial dynamics, poroelastic



Courtesy of A.A. Linninger (University of Illinois at Chicago, IL), B. Sweetman (University of Illinois at Chicago, IL), R. Penn (University of Chicago, Chicago, IL)

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