Computational Haemodynamics—An Introduction - Computational Hemodynamics: Theory, Modelling and Applications - page 8

Fig. 1.6 Wall shear stress distribution plots of carotid bifurcations ( case study 1-8 ) pre- and post-
percutaneous carotid artery angioplasty and stenting ( PTAS ). Contour plots of the wall shear stress
( WSS ) magnitude in dyn/cm 2 averaged over the cardiac cycle before and after carotid artery stent-
ing by PTAS. (Image from Schimmer and Malek 2011)

1.3.4 Plaque Rupture Risk Assessment

Before establishing a numerical simulation to assess plaque mechanical behaviour,
the first step is to extract information on plaque tissue morphology and classifica-
tion, which can be performed by MRI. Coupled with image processing techniques,
high-resolution MRI is capable of classifying different tissue types. This forms the
basis for determining adverse cardiovascular conditions that exceed the normal
threshold for rupture, requiring surgical rectification such as by-pass or stenting.
MR multi-contrast plaque imaging can distinguish plaque components, its mor-
phology, and establish the elastic behaviour of its composites. The mechanical
properties extracted from patient-specific plaque condition can be used as clinical
data for running the computational modelling of plaque response to stress (Fig. 1.7 ).
The morphological plaque severity index (MPSI) and computational plaque
stress index (CPSI) can then be established (Tang et al. 2005c, 2009). The former
index deals with the correlation of plaque morphological characteristics with vul-
nerability, whereas the latter is linked to numerically computed stress level associ-
ated with computationally generated plaque geometry.
Knowledge of diseased vessel structures forms a solid foundation for investi-
gating the pathological development of vascular diseases. This enables effective
characterisation of blood flow for patient specific physiological/pathological con-
ditions. This leads to better surgical planning and post-operation therapy that is
patient specific and customised.
Plaque distribution and its structural components can be characterised by a three
dimensional blood-vessel model with the aim of determining the variable mechani-
cal properties due to changes by the lipid core and calcification contents. Numerical
simulations can identify how cap thickness and calcium distribution in lipids inter-
act to influence biomechanical stress.
Geometric models of non-calcified plaque, and partially and fully calcified
plaque can also be modelled (Fig. 1.8 ). Critical stress analysis of a diseased carotid