Jun-Mei Zhang

Numerical simulation of patient-specific left ventricular model with both mitral and aortic valves by FSI approach

Intraventricular flow is important in understanding left ventricular function; however, relevant numerical simulations are limited, especially when heart valve function is taken into account. In this study, intraventricular flow in a patient-specific left ventricle has been modelled in two-dimension (2D) with both mitral and aortic valves integrated. The arbitrary Lagrangian-Eulerian (ALE) approach was employed to handle the large mesh deformation induced by the beating ventricular wall and moving leaflets. Ventricular wall deformation was predefined based on MRI data, while leaflet dynamics were predicted numerically by fluid-structure interaction (FSI). Comparisons of simulation results with in vitro and in vivo measurements reported in the literature demonstrated that numerical method in combination with MRI was able to predict qualitatively the patient-specific intraventricular flow. To the best of our knowledge, we are the first to simulate patient-specific ventricular flow taking into account both mitral and aortic valves.

Perspective on CFD studies of coronary artery disease lesions and hemodynamics: A review

Coronary artery disease (CAD) is the most common cardiovascular disease. Early diagnosis of CADs physiological significance is of utmost importance for guiding individualized risk-tailored treatment strategies. In this paper, we first review the state-of-the-art clinical diagnostic indices to quantify the severity of CAD and the associated invasive and noninvasive imaging technologies in order to quantify the anatomical parameters of diameter stenosis, area stenosis, and hemodynamic indices of coronary flow reserve and fractional flow reserve. With the development of computational technologies and CFD methods, tremendous progress has been made in applying image-based CFD simulation techniques to elucidate the effects of hemodynamics in vascular pathophysiology toward the initialization and progression of CAD. So then, we review the advancements of CFD technologies in patient-specific modeling, involving the development of geometry reconstruction, boundary conditions, and fluid-structure interaction. Next, we review the applications of CFD to stenotic sites, in order to compute their hemodynamic parameters and study the relationship between the hemodynamic conditions and the clinical indices, to thereby assess the amount of viable myocardium and candidacy for percutaneous coronary intervention. Finally, we review the strengths and limitations of current researches of applying CFD to CAD studies.

Simplified Models of Non-Invasive Fractional Flow Reserve Based on CT Images.

Invasive fractional flow reserve (FFR) is the gold standard to assess the functional coronary stenosis. The non-invasive assessment of diameter stenosis (DS) using coronary computed tomography angiography (CTA) has high false positive rate in contrast to FFR. Combining CTA with computational fluid dynamics (CFD), recent studies have shown promising predictions of FFRCT for superior assessment of lesion severity over CTA alone. The CFD models tend to be computationally expensive, however, and require several hours for completing analysis. Here, we introduce simplified models to predict noninvasive FFR at substantially less computational time. In this retrospective pilot study, 21 patients received coronary CTA. Subsequently a total of 32 vessels underwent invasive FFR measurement. For each vessel, FFR based on steady-state and analytical models (FFRSS and FFRAM, respectively) were calculated non-invasively based on CTA and compared with FFR. The accuracy, sensitivity, specificity, positive predictive value and negative predictive value were 90.6% (87.5%), 80.0% (80.0%), 95.5% (90.9%), 88.9% (80.0%) and 91.3% (90.9%) respectively for FFRSS (and FFRAM) on a per-vessel basis, and were 75.0%, 50.0%, 86.4%, 62.5% and 79.2% respectively for DS. The area under the receiver operating characteristic curve (AUC) was 0.963, 0.954 and 0.741 for FFRSS, FFRAM and DS respectively, on a per-patient level. The results suggest that the CTA-derived FFRSS performed well in contrast to invasive FFR and they had better diagnostic performance than DS from CTA in the identification of functionally significant lesions. In contrast to FFRCT, FFRSS requires much less computational time.

Hemodynamic analysis of patient‐specific coronary artery tree

Local hemodynamic parameters, such as wall shear stress (WSS), oscillatory shear index and relative resident time (RRT), have been linked to coronary plaque initiation and progression. In this study, a left coronary artery tree model was reconstructed from computed tomography angiography images of a patient with multiple stenoses. The geometry of the coronary artery tree model was virtually restored by eliminating the lesions, essentially re-creating the virtually healthy artery anatomy. Using numerical simulations, flow characteristics and hemodynamic parameter distributions in the stenosed and virtually healthy models were investigated. In the virtually healthy artery model, disturbed flows were found at four locations, prone to initialization of plaque formation. Low WSS and high RRT were exhibited in three of the four locations, and high WSS and low RRT were exhibited in the fourth. These findings suggest that coronary plaque is more likely to form in locations with disturbed flow conditions characterized by low WSS and high RRT or high WSS and low RRT. In addition, clinical index of fractional flow reserve was found to significantly correlate with blood flow rate, rather than anatomic parameters, such as diameter stenosis, which implied the importance of hemodynamic environment in stenosis formation.

Automatic localization of the left ventricle from cardiac cine magnetic resonance imaging: a new spectrum-based computer-aided tool.

Traditionally, cardiac image analysis is done manually. Automatic image processing can help with the repetitive tasks, and also deal with huge amounts of data, a task which would be humanly tedious. This study aims to develop a spectrum-based computer-aided tool to locate the left ventricle using images obtained via cardiac magnetic resonance imaging. Discrete Fourier Transform was conducted pixelwise on the image sequence. Harmonic images of all frequencies were analyzed visually and quantitatively to determine different patterns of the left and right ventricles on spectrum. The first and fifth harmonic images were selected to perform an anisotropic weighted circle Hough detection. This tool was then tested in ten volunteers. Our tool was able to locate the left ventricle in all cases and had a significantly higher cropping ratio of 0.165 than did earlier studies. In conclusion, a new spectrum-based computer aided tool has been proposed and developed for automatic left ventricle localization. The development of this technique, which will enable the automatic location and further segmentation of the left ventricle, will have a significant impact in research and in diagnostic settings. We envisage that this automated method could be used by radiographers and cardiologists to diagnose and assess ventricular function in patients with diverse heart diseases.

Coronary artery segmentation via Hessian filter and curve-skeleton extraction

Precise coronary artery segmentation is a prerequisite for quantitatively assessing the severity of coronary artery stenosis. Extracting the centre line of the 3D volumetric coronary artery tree, also named as 3D skeletonization, plays an important role in identify the variations of cross-sectional profile. Typically there are three skeletonization methods, viz. distance transformation, Voronoi method and topological thinning method. All these three skeletonization methods were applied in this study to extract the curve-skeleton of coronary arteries, after segmenting the coronary artery tree with Hessin filter. Among them, topological thinning method is recommended, as it produces reliable and accurate curve-skeleton for vessels with varying size. This will facilitate quantitative assessment of the severity of coronary artery stenosis, help clinical diagnosis and treatment planning of coronary artery disease.

Patient-specific blood flows and vortex formations in patients with hypertrophic cardiomyopathy using computational fluid dynamics

Hypertrophic cardiomyopathy (HCM) is a relatively common genetic cardiac disorder in which a portion of the myocardium becomes hypertrophied. Dynamic left ventricle outflow tract obstruction is present and associated with worsened symptom severity and disease progression. However, its mechanism is still not fully understood, and the complex interaction between the thickened ventricular wall and altered blood flow in patient-specific model has not been studied. In this study, we recruited one patient with HCM and one healthy volunteer who underwent magnetic resonance imaging scans. The patient-specific geometries were reconstructed, and both spatial and temporal interpolations were applied to increase the corresponding resolutions. The results showed that HCM patient had cirrostratus-cloud like vortex structures rather than a major vortex ring observed in healthy subject, which implies that the vortex formation from computational fluid dynamics (CFD) simulation has the potential to diagnose HCM.

Area stenosis associated with non-invasive fractional flow reserve obtained from coronary CT images

Fractional flow reserve (FFR) determined by invasive angiography is the gold standard to assess the severity of coronary artery disease (CAD). FFRCT can be obtained non-invasively by combining computed tomography (CT) images and Computational Fluid Dynamics (CFD) method. In this study, FFRCT was computed for 6 models of patient-specific left coronary artery trees reconstructed from CT images. A total of 12 stenoses were observed. FFR values obtained for 7 of the 12 stenoses during invasive angiography were used as the gold standard for comparison. On a per-stenosis basis, the sensitivity, specificity, positive predictive value and negative predictive value were 50%, 100%, 100% and 83.3% respectively for FFRCT. A weak correlation was found between percent lumen diameter stenosis and FFRCT (r=0.431; p>0.05). However, the correlation between percent lumen area stenosis and FFRCT was significant (r=0.853; p<;0.05). Therefore, non-invasive FFRCT appears to be a promising index to assess the severity of CAD and lumen area has distinct advantages over diameter measurement in terms of anatomy assessment.

Effects of Baffle Configurations on the Performance of a Potable Water Service Reservoir

AbstractBecause a baffle is a device used for altering the flow pattern in a tank, the use of a baffle wall was considered to modify an existing potable water service reservoir operating as a storage tank to achieve better water quality. Therefore, it is of great interest to study the effects of baffle configurations on the performance of the service reservoir. With the advancement of computational science and resources, a Computational Fluid Dynamics (CFD) method has become a reliable alternative to flow and tracer tests. Adopting dynamic meshes, this study investigates the effects of baffles, located at various locations, on the flow pattern and chlorine concentration distribution of a potable water service reservoir in Singapore during the refilling phase. The results of this study show a dual effect of the baffles located at the flow recirculation region. On one hand, it can break up the vortex to shorten the flow path. On the other hand, the velocity magnitude of the fluid is reduced after flowing pa...

Fast Marching and Runge–Kutta Based Method for Centreline Extraction of Right Coronary Artery in Human Patients

The CT angiography (CTA) is a clinically indicated test for the assessment of coronary luminal stenosis that requires centerline extractions. There is currently no centerline extraction algorithm that is automatic, real-time and very accurate. Therefore, we sought to (i) develop a hybrid approach by incorporating fast marching and Runge–Kutta based methods for the extraction of coronary artery centerlines from CTA; (ii) evaluate the accuracy of the present method compared to Van’s method by using ground truth centerline as a reference; (iii) evaluate the coronary lumen area of our centerline method in comparison with the intravascular ultrasound (IVUS) as the standard of reference. The proposed method was found to be more computationally efficient, and performed better than the Van’s method in terms of overlap measures (i.e., OV: