Biomedical Engineering Reference
In-Depth Information
This case study uses the right atrium of the heart as an illustration of flow
quantification and visualization techniques. Specifically, we focus on vortices that
are generated within a heart chamber. Cardiac flow analysis based on vorticity map-
ping can define the flow behaviour within the heart chamber (Wong et al. 2009a;
Wong et al. 2010c). The first stage of flow analysis is to generate the blood flow
field in the cardiac structure based on phase contrast magnetic resonance imaging
and then by numerical simulation. The second stage is to use the flow field for vor-
ticity measurement and visualization. Then, the final stage is to quantify the vortic-
ity field statistically and examine the changes in vorticity over time.
Phase contrast magnetic resonance imaging (MRI) belongs to a class of
experimental flow imaging by means of quantifying the phase shifts in proton
spins of the imaged fluid, and has been widely used to measure flow fields of blood
in the cardiac structures in-vivo (Markl et al. 2007). Another approach to generate
a haemodynamic flow field relies on medical imaging, anatomical reconstruction,
and numerical simulation by CFD. This involves reconstructing the cardiac vessel
geometry from medical imaging whereby blood is transported. The next step is
to mesh the flow volume and establish the boundary flow conditions, which can
be determined by medical imaging measurement, such as Doppler ultrasound or
phase contrast magnetic resonance image data (Marshall et al. 2004b).
Validation of the CFD simulation in human proximal airways with hyperpolar-
ized 3He magnetic resonance phase-contrast velocimetry in-vivo measurements
have shown good agreement (de Rochefort et al. 2007). The flow imaging results
of the cardiovascular structure in-vivo is often taken as benchmark data since blood
velocities are intrinsically measured with good accuracy. The simulation is typical-
ly used as a predictive tool for further detailed analysis that are difficult to measure.
Velocity measurement and mapping systems by phase-contrast-MRI are often used
to validate computational and predictive frameworks with good reliability. The
use of phase-contrast-MRI and CFD can quantify the vortical flow for the cardiac
chamber and may open up new insights into the flow behavior within this anatomy.
7.5.2
Application of Medical Imaging in Computational Heart
Modelling
A realistic right atrium model is reconstructed based on medical imaging (Merrifield
et al. 2004a; Saber et al. 2001). Segmentation of the myocardium was performed
through a series of time-resolved image slices. Imaging modalities for assessment
of cardiac chambers or myocardial function include computed tomography and
MRI, but MRI is superior since the tissue and blood regions are well-distinguished
in terms of boundary image intensity. The geometry is meshed and a CFD simula-
tion is performed.
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