Modelling Arterial Blood Flow in the Brain
In the western world stroke is the third largest cause of death, following heart disease and all forms of cancer, and the largest cause of serious long-term disability. The monetary costs associated with stroke care are considerable and it is projected that if the incidence of stroke continues to increase at the same rate it will more than triple in the next 30 years. There is therefore a great importance on the understanding of factors that increase the risk of stroke and hence how blood is distributed throughout the brain.
The current research is focused on a ring-like arterial structure located in the base of the brain, known as the Circle of Willis.
The function of the Circle of Willis is to distribute oxygenated blood entering through the afferent basilar and internal carotid arteries, to the cerebral territories through three major pairs of efferent arteries known as the anterior, middle and posterior cerebral arteries. The circle is of particular importance because it allows for blood to be re-routed through the anterior and posterior communicating arteries in order to maintain oxygen supply to all of the cerebral territories, should the blood supply through any of the afferent arteries be reduced. Maintaining blood supply is important since even though the brain only comprises approximately 2% of the body’s total mass, it requires approximately 20% of the blood output from the heart, and if the brain is starved of this supply for more than a few minutes brain cells become permanently damaged.
Among the general population, approximately 50% have a complete circle of Willis, where among a multitude of possible anatomical variations, vessels which are greatly reduced in diameter or even completely absent are common, either of which reduces the degree to which blood may be re-routed through the circle. While an individual with one of these variations may, under normal circumstances, suffer no ill effects, there are certain pathological conditions, a build up of atherosclerotic plaque in the afferent arteries, which can present a risk to the person’s health and the possibility of suffering an ischaemic stroke, when compounded with the effects of an absent vessel.
A 3D Model
An advanced 3D computer model has been developed from Magnetic Resonance Imaging (MRI) data and uses a technique known as Computational Fluid Dynamics (CFD) to model the blood flow throughout the circle of Willis. The simulation results give the response of the circle to different pathological conditions, including the combined effects variations in cerebral-vasculature with atherosclerotic plaque build-up. The long term goal of the project involves the development of a clinical diagnostic tool for automatically recreating a 3D model of an individual’s cerebral vasculature, from an MRI scan and using CFD to predict the likelihood of stroke in the short term, or the risk associated with various surgical procedures such as carotid endarterectomy.
This project is under the supervision of Professor Tim David. Postgraduate students working on the project include Steve Moore, Samara Alzaidi, Kate Moorhead, and Jade Arnold. This work is being conducted in cooperation with researchers from NASA Ames Research Center.