Spectral decomposition and illustration-inspired visualisation of highly disturbed cerebrovascular blood flow dynamics

Informed by high-resolution computational fluid dynamics (CFD) simulations, we present a strategy using a temporal filtering approach to examine the three-dimensional structures of velocity fluctuations filtered based on the global spectral content. Research suggests the presence of transient, turbulent-like flow instabilities at a range of frequencies from 10 Hz up to 1 kHz, some of which are associated with clinical reports of aneurysm vibration or <i>‘bruits’</i>, and which may promote aneurysm growth or rupture. To isolate and visualise these instabilities with respect to their frequency, the filtering technique presented in this work is applied to the flow simulations of three middle cerebral artery (MCA) aneurysms and three internal carotid artery (ICA) siphons. Vortex cores associated with the different frequency bands are then visualised together to highlight their spatiotemporal interactions. Inspired by visual styles of illustration, we present a rendering strategy depicted with outlines, silhouettes and two-tone cel-shading to prevent occlusion and emphasise the resulting flow structures of importance while the other details are given less weight to de-emphasise their presence in the background of the image plane. Reinforcing previous studies in the literature, the current work also confirmed the presence of flow fluctuations to the order of up to 1 kHz when modelled adequately using high-resolution CFD simulations.