The financial support of the European Commission is gratefully acknowledged. Material in this presentation reflects only the author’s views and the Commission is not liable for any use that may be made of the information contained – A TOOL FOR INVESTIGATING HAEMODYNAMICS IN INTRACRANIAL ANEURYSMS Paul Summers, Paul Watton, James Byrne (University of Oxford) Alessandro Chiarini (B3C)

ConfidentialCopyright © 2006 Cebral et al Growth Rupture Stability Boundary Conditions

vascular modelling toolkit An integrated medical image-based computational hemodynamic simulation tool Import Images Database or Local Files Image Segmentation Surface Editing Image Segmentation Surface Editing Model setting (centerline, boundary conditions) Automated mesh generation Submission for CFD simulation (to Ansys) Model setting (centerline, boundary conditions) Automated mesh generation Submission for CFD simulation (to Ansys) Morphology Description Interactive visualization of haemodynamic parameters (pressure, flow pattern, WSS) Record process

Extract vessel surface & Remove irrelevant vasculature Input: DICOM or Philips v3d Segmentation algorithm is nearly user independent → repeatable 3DXA preferable, but bad images – bad / hard segmentation Import 3D Angiogram MRA CTA 3dXA

Morphological analysis 5 DefineNeck Indicate Dome Compute Zemike Descriptors Danger: poor segmentation (poor images) → bad shape Effect of Subjective neck location? - Compute Cross-section Diameters - Calipers for measuring size.

Grids, meshes & Boundary Conditions: What are they? flowrate waveform flow rate [ml s -1 ] t [s] pressure waveform pressure [mmHg] t [s] Inflow and outflow data can come from: Patient-specific measures Average/population based data Computed by a model of the systemic tree (1D Circulation Model) -MOST HAEMODYNAMIC ANALYSES ASSUME RIGID WALLS AND DO NOT CONSIDER THE SIGNIFICANCE OF THE CYCLIC STRETCH OF THE CELLS An outlet pressure of 0mmHg is used for computational simulations, but causes misleading spatial pressure results

Create centerline, 1D model, and apply boundary conditions MCA 1D model result in vivo Doppler in vivo Doppler 1D model result ICA Time per case preparation ≈ 40 minutes.

Export model to the solver & Launch analysis Computation times can range from hours to days. Ansys  Solver (not included) or Problem Definition File A solution! not “The solution” - Converged - Stable across mesh sizes - May show very slight differences between runs flowrate waveform flow rate [ml s -1 ] t [s] pressure waveform pressure [mmHg] t [s]

Visualisation pressure WSS pathlines - gauge

“…a higher pressure area (white arrow) on the wall opposite to the blood stream coming from the right vertebral artery… may lead to subsequent growth of the aneurysm at this location.” SIMILAR EXAMPLES: Neuroradiology (2007,2008) AJNR (2004) IS IT REALLY PRONOUNCED ? Parent artery: 124mmHg Aneurysm max: 126mmHg Increase in load (e.g. strenuous activity, hypertension) Blood pressure spiking when on the toilet. “Doctors in Calcutta, India found a third of stroke deaths occurred while people were squatting.” - Decrease in strength (deleterious growth and remodelling) Aneurysm rupture associated with increase in number of secondary blebs on dome. Increased collagenase activity

Structural analysis (Quasi-static: Systolic/diastolic deformations) MECHANOBIOLOGY Growth & Remodelling Matrix/cell: (cyclic) stretch/stress Haemodynamic analysis Mechanical environment of vascular cells update constitutive model export aneurysm geometry Insert aneurysm geometry into physiological geometry. Mesh domain. Solve flow. WSS, WSSG, OSI, GON, AFI, RRT

MRA data  Ansys ICEM   Aneurysm Growth Model* Elastin Concentration Hypothesis (Low WSS drives elastin degradation) + Patient specific haemodynamics = Qualitatively similar evolution of geometry *Watton et al (2009), ASME J Biomech Eng, 131(10): WSS

@neuEndo: Virtual Stenting:subject-specific intervention planning and stent selection

and vmtk are accessible points of entry to CFD preparation for the aneurysm research is suited to newcomers, but can be used in multicentre work (> 300 cases Neither includes a solver. There remains a critical need for combined medical, and engineering expertise in running the simulations, interpretation, and for validation studies on use and application. B3C plans commercial version (AIMA), beta version for non-clinical use available through at least ESMINT: working group on ConfidentialCopyright ©

Recognition! D Testi, M Viceconti B3C, IT A Marzo, R Hose, P Singh, P Lawford University of Sheffield, UK A Radaelli, M-C Villa Uriol, I Larribide, A Franji Universitat Pompeu Fabra, ES C Bludszuweit-Philipp ASD DE Y Ventikos, T Bowker University of Oxford L Augsburger University of Geneva CH N Stergiopolous EPFL CH D Sweeney IDAC IE Invitation! (trying them is free!): CPU ≥ 2GHz, memory ≥ GB, download and try, then take your prepared model to a friendly fluid dynamicist to ConfidentialCopyright ©