Houston Methodist. Leading Medicine.
Houston Methodist. Leading Medicine

Department of Neurosurgery

Computational Hemodynamics Laboratory

The Computational Hemodynamics Lab of the Department of Neurosurgery focuses on simulating blood flow in cerebral aneurysms with the goal to develop a better understanding of the etiology, progression and treatment options for this devastating disease.

Background

The rupture of an intracranial aneurysm is a serious clinical event leading to subarachnoid hemorrhage (SAH) with potential fatal outcome. While symptomatic, large aneurysms are usually treated, asymptomatic, small aneurysms pose a challenge, as an accurate method for the calculation of rupture risk for a particular aneurysm is currently unavailable.

In addition to other factors, hemodynamics in aneurysm is thought to contribute to aneurysm formation, growth and rupture. For instance, bench-top experiments have demonstrated that endothelial cells respond to shearing forces of the time-varying blood flow, mural cells feel stretch and shearing forces from transmural filtration, platelets may be activated by shear forces and biomechanical factors have been demonstrated to be of importance in the adhesion process of monocytes.

As hemodynamic measurements are difficult to obtain in-vivo in a non-invasive manner, computational techniques utilizing patient-derived geometries and physiological flows, such as computational fluid dynamics (CFD), may pose a viable alternative for calculating blood dynamics in cerebral aneurysms (figure 1) and for investigating the influence of hemodynamic parameters on aneurysm formation [1]. A potential means for validating these simulations is phase contrast magnetic resonance imaging (pcMRI) in which blood flow velocities inside the aneurysm and the parent artery can be directly measured (figure2) [2 ,3].

Computational Hemodynamics Lab | Dept of Neurosurgery
Figure 1: Wall shear stresses (WSS) and pathlines during systole in an ACOM aneurysm (invited presentation at the Fluent user meeting, San Diego

Computational Hemodynamics Lab | Dept of Neurosurgery
Figure 2: Velocity images measured with pcMRI (lower left) and simulated with CFD (lower right) of the aneurysm shown in the upper left. Images were acquired at two planes dissecting the aneurysm (shown in the schematic in the upper right), from [1].

Current Projects

Recently, a new treatment option utilizing a flow diverter, i.e. dense cylindrical mesh placed across the aneurysm ostium, has been approved for treatment. Consequent hemodynamic alterations, in particular changes in pressures and velocities inside the aneurysm dome, still lack detailed understanding but may be of great importance for long-term outcome. In collaboration with the Siemens AG, CFD visualization within the Inspace environment was developed (figure 3) and currently a dedicated CFD research prototype is being testing for the simulations of hemodynamics in cerebral aneurysms before and after flow diverter placement (figure 4).  Of particular interest in this research project is to evaluate if hemodynamic parameters at the aneurysm ostium may be predictive of hemodynamic alterations inside the aneurysm after flow diverter placement [4].

Computational Hemodynamics Lab | Dept of Neurosurgery
Figure 3: Implementation of CFD results into the Siemens Inspace post-processing environment (research prototype, not for clinical use).

As images are acquired at different time points (phases) during the cardiac cycle, pcMRI in addition to velocities, can also visualize aneurysm wall dynamics. It may therefore aid in identifying wall segments with high mobility potentially indicating a thin, weak wall segment which was demonstrated in a study of seven intracranial aneurysms. Maximum wall distension was found to range from 0.2 to 1.6 mm and maximum wall contraction from 0.3 to 1.9 mm [5].

Computational Hemodynamics Lab | Dept of Neurosurgery
Figure 4: Screenshot of post-simulation visualization of CFD results within the CFD research prototype (Siemens AG).

Collaborative Projects

The computational tools developed for simulating blood flow dynamics in cerebral aneurysm were applied in collaborative projects to other vascular diseases: Hemodynamic alterations with treatment and disease progression were quantified in collaboration with the Department of Vascular Surgery at the Houston Methodist DeBakey Heart & Vascular Center [6], with the Department of Radiology at the University of Heidelberg, Germany  [7]and the Department of Radiology at the University of Basel, Switzerland [8]. Changes in the hemodynamics of the ascending aorta after LVAD treatment was characterized using CFD in collaboration with the Houston Methodist DeBakey Heart & Vascular Center and the Department of Cardiac Surgery at the University of Heidelberg, Germany [9].

References

  • Mantha A, Karmonik C, Benndorf G, Strother C, Metcalfe R. Hemodynamics in a cerebral artery before and after the formation of an aneurysm. AJNR Am J Neuroradiol. 2006 May;27(5):1113-8.
  • Karmonik C, Klucznik R, Benndorf G. Blood Flow in Cerebral Aneurysms: Comparison of Phase Contrast Magnetic Resonance and Computational Fluid Dynamics - Preliminary Experience. Rofo. 2008 Mar;180(3):209-15.
  • Karmonik C, Yen C, Grossman RG, Klucznik R, Benndorf G.   Intra-aneurysmal flow patterns and wall shear stresses calculated with computational flow dynamics in an anterior communicating artery aneurysm depend on knowledge of patient-specific inflow rates. Acta Neurochir (Wien). 2009 May;151(5):479-85; discussion 485. Epub 2009 Apr 3
  • Karmonik C, Chintalapani G, Redel T, Zhang YJ, Diaz O, Klucznik R, Grossman RG. Hemodynamics at the Ostium of Cerebral Aneurysms with Relation to Post-Treatment Changes by a Virtual Flow Diverter:  A Computational Fluid Dynamics Study. Annual  Meeting, EMBC 2013, Osaka, Japan.
  • Karmonik C, Diaz O, Grossman R, Klucznik R. In-Vivo Quantification of Wall Motion in Cerebral Aneurysms from 2D Cine Phase Contrast Magnetic Resonance Images. Rofo. 2010 Feb;182(2):140-50. Epub 2009 Oct 26.
  • Karmonik C, Bismuth J, Shah DJ, Davies MG, Purdy D, Lumsden AB. Computational study of haemodynamic effects of entry- and exit-tear coverage in a DeBakey type III aortic dissection: technical report. Eur J Vasc Endovasc Surg. 2011 Aug;42(2):172-7. Epub 2011 May 6
  • Karmonik C,  Partovi S, Mueller-Eschner M, Bismuth J, Davies MG, Shah DJ, Loebe M, Boeckler D, Lumsden AB, von Tengg-Kobligk. Longitudinal Computational Fluid Dynamics Study of Aneurysmal Dilatation in a Chronic DeBakey Type III Aortic Dissection. J Vasc Surg, 2012 Jul;56(1):260-263.e1. Epub 2012 May 10
  • Karmonik C, Partovi S, Davies MG, Bismuth J, Shah DJ, Bilecen D, Staub D, Noon GP, Loebe M, Bongartz G, Lumsden AB. Integration of the computational fluid dynamics technique with MRI in aortic dissections, Magn Reson Med, 2012 Jun 14. doi: 10.1002/mrm.24376
  • Karmonik C, Partovi S, Loebe M, Schmack B, Ghodsizad A, Robbin MR, Noon GP, Kallenbach K, Karck M, Davies MG, Lumsden AB. Influence of LVAD Cannula Outflow Tract Location on Hemodynamics in the Ascending Aorta -  A Patient Specific Computational Fluid Dynamics Approach. ASAIO Journal 2012, accepted.