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Modelling of Endovascular Coil Embolisation of Cerebral Aneurysms

Nikolaos Kakalis1, Tim Bowker1, Aristotelis Mitsos2, Paul Summers2, James Byrne2, and Yiannis Ventikos1. (1) Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, United Kingdom, (2) Neuroradiology & Radcliffe Infirmary, University of Oxford, Woodstock Road, Oxford, OX2 6HE, United Kingdom

Cerebral aneurysms are pathological deformations of the arterial wall in blood vessels feeding the brain, with a high risk of rupture causing subarachnoid haemorrhage and mortality or severe morbidity. To date, the prevailing treatment technique for ruptured or detected unruptured aneurysms is the endovascular coil embolisation. In this method a micro-catheter is navigated through the vasculature into the cerebral aneurysm where it releases detachable coils. The coils induce blood to thrombose, thus isolating the aneurysm from the patient's circulation. Realistic and accurate computational models, able to describe and predict this process, the various interactions and its significance do not exist up to date.

In this paper, we introduce a novel computational methodology for patient-specific modelling of the dynamic behaviour of the combined vasculature-catheter system. The first step of our approach is the construction of the anatomically accurate vasculature geometry of interest. We employ rotational 3D-DSA datasets (e.g. from magnetic resonance imaging or computer tomography scans) of the aneurismal area; these are segmented to provide an adequately fine surface description. The geometry of a micro-catheter is virtually inserted and placed to a characteristic coil release position. The combined, lumen-catheter domain is subsequently discretised into tetrahedral volume grids. At a second step, a haemodynamic model is applied to describe the flow, pressure and force fields of the system as a function of time in the cardiac cycle.

The significance and capabilities of our developments are demonstrated via their use for modelling the haemodynamic effects of the embolisation of an aneurysm at the anterior communicating and middle cerebral artery. The calculations reveal that the introduction of the micro-catheter increases significantly the wall shear stress and pressure at the parent artery, aneurysm ostium and neck, while the flow and loads in the sac are reduced. Complex haemodynamic patterns are observed, and the characterisation of loads on the catheter, local flow patterns induced by the catheter and blood flow lines is studied. Comparisons with the catheter-free case illustrate the consequences of catherisation. Such insights provide the physicians with improved understanding of the consequences and risks of the treatment and are expected to lead to the development of new techniques and devices. Extensions of the model to account for the vascular biochemical mechanisms of thrombosis are also considered.