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Khalafvand S.S.,Nanyang Technological University | Ng E.Y.-K.,Nanyang Technological University | Zhong L.,Cardiac Mechanics Engineering and Physiology Unit
Proceedings - 2012 International Conference on Biomedical Engineering and Biotechnology, iCBEB 2012 | Year: 2012

This study was to simulate the left ventricular (LV) flow in the human heart via combination of computational fluid dynamics (CFD) and magnetic resonance imaging (MRI). MRI was performed for a heart failure (HF) patient before and 4- month after surgical ventricular restoration. The geometry included LV, left atrium (LA) and ascending aorta derived for 25 frames during one cycle from MRI data. After reconstruction of time dependent geometries and producing intermediate grids, 3D CFD modeling is performed for both before and after surgery. Intermediate geometries are generated to provide fine enough time steps for CFD modeling and discontinue time step fashion is used. The results showed that velocity of blood in LV increased after surgery and more powerful vortices exist than before surgery LV. Combined CFD/MRI for patients before and after surgery with different heart diseases could facilitate better understanding of flow pattern and research into ways to optimize and refine surgical treatment approaches in the future. © 2012 IEEE.

Tan M.-L.,Institute of High Performance Computing of Singapore | Su Y.,Institute of High Performance Computing of Singapore | Lim C.-W.,Institute of High Performance Computing of Singapore | Selvaraj S.K.,Institute of High Performance Computing of Singapore | And 2 more authors.
PLoS ONE | Year: 2013

This paper describes an automatic algorithm that uses a geometry-driven optimization approach to restore the shape of three-dimensional (3D) left ventricular (LV) models created from magnetic resonance imaging (MRI) data. The basic premise is to restore the LV shape such that the LV epicardial surface is smooth after the restoration and that the general shape characteristic of the LV is not altered. The Maximum Principle Curvature (k1) and the Minimum Principle Curvature (k2) of the LV epicardial surface are used to construct a shape-based optimization objective function to restore the shape of a motion-affected LV via a dual-resolution semi-rigid deformation process and a free-form geometric deformation process. A limited memory quasi-Newton algorithm, L-BFGS-B, is then used to solve the optimization problem. The goal of the optimization is to achieve a smooth epicardial shape by iterative in-plane and through-plane translation of vertices in the LV model. We tested our algorithm on 30 sets of LV models with simulated motion artifact generated from a very smooth patient sample, and 20 in vivo patient-specific models which contain significant motion artifacts. In the 30 simulated samples, the Hausdorff distances with respect to the Ground Truth are significantly reduced after restoration, signifying that the algorithm can restore geometrical accuracy of motion-affected LV models. In the 20 in vivo patient-specific models, the results show that our method is able to restore the shape of LV models without altering the general shape of the model. The magnitudes of in-plane translations are also consistent with existing registration techniques and experimental findings. © 2013 Tan et al.

Zhang J.-M.,Cardiac Mechanics Engineering and Physiology Unit | Zhang J.-M.,National University of Singapore | Khoo B.C.,National University of Singapore | Lee H.P.,National University of Singapore | And 3 more authors.
Journal of Environmental Engineering (United States) | Year: 2013

A major water-quality concern in a potable water service reservoir is the potential loss of chlorine residual, which is closely related to the flow pattern. In this article, the effects of operation and baffling on the flow pattern and chlorine-concentration distribution in a potable water service reservoir are reported. Using a computational fluid dynamics (CFD) method coupled with dynamic meshes, actual service conditions are mimicked, which have seldom been reported in the literature. First, this article provides an insight into why manipulating the valve located at the inlet can be beneficial in enhancing water quality in the long run. An explanation based on the simulation results suggests that manipulating the valve located at the inlet can lead to the evolution and migration of the vortices in the service reservoir, which would then allow water with prolonged age to flow out of the reservoir. This is significant for the operation of service reservoirs. Second, it explores the possibility of retrofitting a service reservoir with baffle walls to minimize the probability of seriously diminished water quality resulting from poor mixing and excessive aging. Although adding baffle walls in the flow-recirculation regions is found to break up the vortices and thus shorten the flow path, the fluid-velocity magnitude is reduced after flowing past the baffle walls. The outcome of these conflicting effects may eventually lead to a diminished effluent chlorine concentration after adding the baffle walls. © 2013 American Society of Civil Engineers.

Kabinejadian F.,National University of Singapore | Ghista D.N.,Education Committee | Su B.,Cardiac Mechanics Engineering and Physiology Unit | Kaabi Nezhadian M.,National University of Singapore | And 4 more authors.
Medical Engineering and Physics | Year: 2014

This study documents the superior hemodynamics of a novel coupled sequential anastomoses (SQA) graft design in comparison with the routine conventional end-to-side (ETS) anastomoses in coronary artery bypass grafts (CABG). The flow fields inside three polydimethylsiloxane (PDMS) models of coronary artery bypass grafts, including the coupled SQA graft design, a conventional ETS anastomosis, and a parallel side-to-side (STS) anastomosis, are investigated under pulsatile flow conditions using particle image velocimetry (PIV). The velocity field and distributions of wall shear stress (WSS) in the models are studied and compared with each other. The measurement results and WSS distributions, computed from the near wall velocity gradients reveal that the novel coupled SQA design provides: (i) a uniform and smooth flow at its ETS anastomosis, without any stagnation point on the artery bed and vortex formation in the heel region of the ETS anastomosis within the coronary artery; (ii) more favorable WSS distribution; and (iii) a spare route for the blood flow to the coronary artery, to avoid re-operation in case of re-stenosis in either of the anastomoses. This in vitro investigation complements the previous computational studies of blood flow in this coupled SQA design, and is another necessary step taken toward the clinical application of this novel design. At this point and prior to the clinical adoption of this novel design, in vivo animal trials are warranted, in order to investigate the biological effects and overall performance of this anastomotic configuration in vivo. © 2014 IPEM.

Su B.,National University of Singapore | Chua L.P.,Nanyang Technological University | Zhong L.,Cardiac Mechanics Engineering and Physiology Unit
Journal of Mechanics in Medicine and Biology | Year: 2013

Most axial flow blood pumps basically consist of a straightener, an impeller, and a diffuser. The diffuser plays a very important role in the performance of the pump to provide an adequate pressure head and to increase the hydraulic efficiency. During the development of an axial flow blood pump, irregular flow field near the diffuser hub is not desirable as it may induce thrombosis. In order to avoid this phenomenon, two approaches were adopted. In the first approach, the number of the diffuser blades was increased from three (B3, baseline model) to five (B5 model). It was observed that the flow field was improved, but the irregular flow patterns were not completely eliminated. In the second approach, we detached the blades from the diffuser hub (B3C2 model), which was integrated and rotated with the impeller hub. It was found that the rotary diffuser hub significantly improved the flow field, especially near the diffuser hub. Besides the detailed flow fields, the hydraulic and hematologic performances at various flow conditions were also estimated using computational fluid dynamics (CFD). Although each design has its own advantages and disadvantages, the B5 model was superior based on a comparative overview. © 2013 World Scientific Publishing Company.

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