Vinh-Tan Nguyen

A semi-automated method for patient-specific computational flow modelling of left ventricles.

Patient-specific computational fluid dynamics (CFD) modelling of the left ventricle (LV) is a promising technique for the visualisation of ventricular flow patterns throughout a cardiac cycle. While significant progress has been made in improving the physiological quality of such simulations, the methodologies involved for several key steps remain significantly operator-dependent to this day. This dependency limits both the efficiency of the process as well as the consistency of CFD results due to the labour-intensive nature of current methods as well as operator introduced uncertainties in the modelling process. In order to mitigate this dependency, we propose a semi-automated method for patient-specific computational flow modelling of the LV. Using magnetic resonance imaging derived coarse geometry data of a patients LV endocardium shape throughout a cardiac cycle, we then proceed to refine the geometry to eliminate rough edges before reconstructing meshes for all time frames and finally numerically solving for the intra-ventricular flow. Using a sample of patient-specific volunteer data, we demonstrate that our semi-automated, minimal operator involvement approach is capable of yielding CFD results of the LV that are comparable to other clinically validated LV flow models in the literature.

A Patient-Specific Computational Fluid Dynamic Model for Hemodynamic Analysis of Left Ventricle Diastolic Dysfunctions

Abstract This work presents a computational fluid dynamic (CFD) model to simulate blood flows through the human heart’s left ventricles (LV), providing patient-specific time-dependent hemodynamic characteristics from reconstructed MRI scans of LV. These types of blood flow visualization can be of great asset to the medical field helping medical practitioners better predict the existence of any abnormalities in the patient, hence offer an appropriate treatment. The methodology employed in this work processed geometries obtained from MRI scans of patient-specific LV throughout a cardiac cycle using computer-aided design tool. It then used unstructured mesh generation techniques to generate surface and volume meshes for flow simulations; thus provided flow visualization and characteristics in patient-specific LV. The resulting CFD model provides three dimensional velocity streamlines on the geometries at specific times in a cardiac cycle, and they are compared with existing literature findings, such as data from echocardiography particle image velocimetry. As an important flow characteristic, vortex formation of the blood flow of healthy as well as diseased subjects having a LV dysfunction condition are also obtained from simulations and further investigated for potential diagnosis. The current work established a pipeline for a non-invasive diagnostic tool for diastolic dysfunction by generating patient-specific LV models and CFD models in the spatiotemporal dimensions. The proposed framework was applied for analysis of a group of normal subjects and patients with cardiac diseases. Results obtained using the numerical tool showed distinct differences in flow characteristics in the LV between patient with diastolic dysfunction and healthy subjects. In particular, vortex structures do not develop during cardiac cycles for patients while it was clearly seen in the normal subjects. The current LV CFD model has proven to be a promising technology to aid in the diagnosis of LV conditions leading to heart failures.

Comparison of hinge microflow fields of bileaflet mechanical heart valves implanted in different sinus shape and downstream geometry

The characterization of the bileaflet mechanical heart valves (BMHVs) hinge microflow fields is a crucial step in heart valve engineering. Earlier in vitro studies of BMHV hinge flow at the aorta position in idealized straight pipes have shown that the aortic sinus shapes and sizes may have a direct impact on hinge microflow fields. In this paper, we used a numerical study to look at how different aortic sinus shapes, the downstream aortic arch geometry, and the location of the hinge recess can influence the flow fields in the hinge regions. Two geometric models for sinus were investigated: a simplified axisymmetric sinus and an idealized three-sinus aortic root model, with two different downstream geometries: a straight pipe and a simplified curved aortic arch. The flow fields of a 29-mm St Jude Medical BMHV with its four hinges were investigated. The simulations were performed throughout the entire cardiac cycle. At peak systole, recirculating flows were observed in curved downsteam aortic arch unlike in straight downstream pipe. Highly complex three-dimensional leakage flow through the hinge gap was observed in the simulation results during early diastole with the highest velocity at 4.7 m/s, whose intensity decreased toward late diastole. Also, elevated wall shear stresses were observed in the ventricular regions of the hinge recess with the highest recorded at 1.65 kPa. Different flow patterns were observed between the hinge regions in straight pipe and curved aortic arch models. We compared the four hinge regions at peak systole in an aortic arch downstream model and found that each individual hinge did not vary much in terms of the leakage flow rate through the valves.

Risk of Thrombosis in Downstream Flow of Mechanical Aortic Valves: A Computational Approach

Abstract Different types of artificial prosthetic heart valves have been implanted to replace defective heart valves since the 1960s. Mechanical heart valves, especially bileaflet mechanical heart valve (BMHV) designs, remain the most prevalently used due to their strength and durability. However, there is always a risk of blood clot formation after a mechanical heart valve is implanted. This chapter focuses on the use of an Arbitrary Lagrangian–Eulerian method with moving mesh technique using an open source software, OpenFOAM. The effects of downstream flow and blood shear on the widely used BMHV and trileaflet mechanical heart valve design are compared. Also, the effects of implantation angles of mechanical aortic valves on flow patterns and blood shear are discussed. It is aimed that the risk of thrombosis can be minimized through valve designs.