Comparison of 4D Phase-Contrast MRI Flow Measurements to Computational Fluid Dynamics Simulations of Cerebrospinal Fluid Motion in the Cervical Spine

Abstract

Cerebrospinal fluid (CSF) dynamics in the cervical spinal subarachnoid space (SSS) have been thought to be important to help diagnose and assess craniospinal disorders such as Chiari I malformation (CM). In this study we obtained time-resolved three directional velocity encoded phase-contrast MRI (4D PC MRI) in three healthy volunteers and four CM patients and compared the 4D PC MRI measurements to subject-specific 3D computational fluid dynamics (CFD) simulations. The CFD simulations considered the geometry to be rigid-walled and did not include small anatomical structures such as nerve roots, denticulate ligaments and arachnoid trabeculae. Results were compared at nine axial planes along the cervical SSS in terms of peak CSF velocities in both the cranial and caudal direction and visual interpretation of thru-plane velocity profiles. 4D PC MRI peak CSF velocities were consistently greater than the CFD peak velocities and these differences were more pronounced in CM patients than in healthy subjects. In the upper cervical SSS of CM patients the 4D PC MRI quantified stronger fluid jets than the CFD. Visual interpretation of the 4D PC MRI thru-plane velocity profiles showed greater pulsatile movement of CSF in the anterior SSS in comparison to the posterior and reduction in local CSF velocities near nerve roots. CFD velocity profiles were relatively uniform around the spinal cord for all subjects. This study represents the first comparison of 4D PC MRI measurements to CFD of CSF flow in the cervical SSS. The results highlight the utility of 4D PC MRI for evaluation of complex CSF dynamics and the need for improvement of CFD methodology. Future studies are needed to investigate whether integration of fine anatomical structures and gross motion of the brain and/or spinal cord into the computational model will lead to a better agreement between the two techniques.

Cerebrospinal Fluid Flow Impedance is Elevated in Type I Chiari Malformation

“…It has been shown that CFD may underestimate the velocity field in rigid-wall SSS models compared to velocities observed in vivo in the SSS using 4D pcMRI [10]. Thus, pressure gradients and, consequently, LI may have been underestimated by this particular CFD methodology.…”

“…Thus, pressure gradients and, consequently, LI may have been underestimated by this particular CFD methodology. Further, bulk neural tissue displacement in the spinal cord and cerebellar tonsils throughout the cardiac cycle in the rostrocaudal direction ranging from 0 to 0.6 mm has been documented for CMI patients and healthy subjects [10,[24][25][26]29]. This data suggest that elastic elements could be added to the boundary conditions that in turn may impact the pressure and velocity fields.…”

“…Although the pulsatile CSF stroke volume is only $1 cc with each cardiac cycle [10,11], the partial stenosis near the CVJ causes elevated CSF pressure gradients [12,13] that can result in severe neurologic consequences. At present, MRI techniques are being developed to measure CSF pressure gradients noninvasively [14], but these methods are not in standard use and have not been validated.…”

Effect of endoscopic third ventriculostomy on cerebrospinal fluid pressure in the cerebral ventricles

“…Mesh sensitivity was also performed by considering three different discretization schemes, as shown in Table 2. The estimation of the relative error of the flow rate introduced by grid and time discretization was calculated at the center of the cerebral ventricles in the model, using the following formula [9]:…”

A robust comparison approach of velocity data between MRI and CFD based on divergence-free space projection

“…Although such combined studies are under extensive research, a reasonable comparison method has not yet been developed. Most of these works do either not describe in detail how the comparisons were achieved exactly or perform visual interpretation [2,3,4], whereas some other works compare velocity magnitude profiles and/or peak-velocities [5,6], linear correlation coefficients [7] or volumetric flow rates [8]. Most of these comparisons are performed on 2D planes, do not define any norm or do not consider flow properties.…”