Biomedical Engineering Reference
In-Depth Information
the brain, thereby ensuring its survival and functioning. To better understand the
physiological aspects of the carotid artery, detailed blood flow patterns from the
entrance of the common carotid artery (CCA) through to the internal carotid ar-
tery (ICA) and external carotid artery (ECA) can provide data that is pertinent to
the prediction of atherosclerosis. Because of the inter-subject variations inherent
between carotid arterial geometries, the numerical results herein are compared
with experimental data available in literature to complement and reinforce the
current knowledge base.
The physics, numerical and CFD setup details that are needed in order to study
the effects of morphological differences in the patient-specific carotid arteries on
the blood flow and their fluid mechanical properties are discussed. Geometrical dif-
ferences are also compared with available data in the literature. Additionally, varia-
tions in the flow patterns and flow features such as pressure drop, wall shear stress,
velocity, and flow distribution between the internal and external carotid arteries, as
well as the different geometries are also presented. The flow in the arterial region
is studied in particular detail to provide better insight into its biofluid mechanical
properties.
This case study is composed of three stages: three-dimensional artery reconstruc-
tion, downstream vascular flow resistance modelling, and haemodynamic analysis
of the carotid artery. We shall examine each of these stages sequentially.
7.2.1
Physiologically Realistic Geometrical Reconstruction
from MRI
The medical image reconstruction for modelling a blood vessel to use in CFD has
rapidly developed in recent decades. With the development of modern imaging
technology, especially magnetic resonance imaging (MRI) and computed tomog-
raphy (CT), it is now possible to quantify arterial blood flow in subject-specific
physiologic models (Philips Medical Systems Clinical Education 1984; Powell
et al. 2000). For three-dimensional numerical studies, CFD models of the carotid
artery can be constructed from MRI or CT images (Merrifield et al. 2004b). Imag-
ing data can be stored in the Digital Imaging and Communication in Medicine (DI-
COM) format. The DICOM format file contains two parts: the header which stores
detailed information about the patient such as name, type of scan, dimension of the
image, image position, and so forth. The second data set contains information of
each scanned image.
Segmentation of the MRI was required to extract the geometry of the carotid ves-
sels. The segmentation process includes thresholding and region growing (Gonzalez
and Woods 2002), followed by 3D anatomical reconstruction (Chandran et al. 2006)
to obtain a very coarse solid model. During thresholding, a range of gray scale
values are selected such that the region to be selected is of best contrast. A sche-
matic diagram depicting the segmentation of magnetic resonance images at vari-
ous locations of the carotid bifurcation is shown in Fig.
7.1
. After the regions of
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