Special issue on patient‐specific computational modelling

Numer Methods Biomed Eng

Yeo

Bevan

et al. 2011

SUMMARYIn this paper, a robust and semi-automatic modelling pipeline for blood flow through subject-specific arterial geometries is presented. The framework developed consists of image segmentation, domain discretization (meshing) and fluid dynamics. All the three subtopics of the pipeline are explained using an example of flow through a severely stenosed human carotid artery. In the Introduction, the state-of-the-art of both image segmentation and meshing is presented in some detail, and wherever possible the advantages and disadvantages of the existing methods are analysed. Followed by this, the deformable model used for image segmentation is presented. This model is based upon a geometrical potential force (GPF), which is a function of the image. Both the GPF calculation and level set determination are explained. Following the image segmentation method, a semi-automatic meshing method used in the present study is explained in full detail. All the relevant techniques required to generate a valid domain discretization are presented. These techniques include generating a valid surface mesh, skeletonization, mesh cropping, boundary layer mesh construction and various mesh cosmetic methods that are essential for generating a high-quality domain discretization. After presenting the mesh generation procedure, how to generate flow boundary conditions for both the inlets and outlets of a geometry is explained in detail. This is followed by a brief note on the flow solver, before studying the blood flow through the carotid artery with a severe stenosis.

Section: Introductionmentioning

confidence: 99%

Modelling pipeline for subject‐specific arterial blood flow—A review

Numer Methods Biomed Eng

Yeo

Bevan

et al. 2011

“…A subject-specific model may be defined as a model in which subject-specific information, such as a scan of an artery is used [1][2][3][4][5][6][7][8][9][10][11][12]. A scan-based, subject-specific computational modelling approach includes three stages.…”

Section: Introductionmentioning

confidence: 99%

Semi‐automatic surface and volume mesh generation for subject‐specific biomedical geometries

Numer Methods Biomed Eng

Nithiarasu

2011

An overview of surface and volume mesh generation techniques for creating valid meshes to carry out biomedical flows is provided. The methods presented are designed for robust numerical modelling of biofluid flow through subject-specific geometries. The applications of interest are haemodynamics in blood vessels and air flow in upper human respiratory tract. The methods described are designed to minimize distortion to a given domain boundary. They are also designed to generate a triangular surface mesh first and then volume mesh (tetrahedrons) with high quality surface and volume elements. For blood flow applications, a simple procedure to generate a boundary layer mesh is also described. The methods described here are semi-automatic in nature because of the fact that the geometries are complex, and automation of the procedures may be possible if high quality scans are used.

“…It is apparent that accurate calculation of fluid flow and related forces plays an important role in both research areas. The emerging area of subject-specific modelling technology is increasingly playing a greater role in precisely calculating fluid flow and related forces (Steinman, 2002;Cebral et al, 2003;Mynard and Nithiarasu, 2008;Taylor and Figueroa, 2009;Taylor and Steinman, 2010;Gambaruto et al, 2010;Nithiarasu and Löhner, 2010;Radaelli and Peiro, 2010;Gee et al, 2010;Mut et al, 2010;Takizawa et al, 2010). In addition to accurate segmentation of geometries, flow boundary conditions and the location at which such boundary conditions are applied may also determine the accuracy of flow calculations.…”

Section: Introductionmentioning

confidence: 99%

Influences of domain extensions to a moderately stenosed patient‐specific carotid bifurcation

Bevan

Nithiarasu

International Journal of Numerical Methods for Heat &Amp; Fluid Flow

et al. 2011

Self Cite

Purpose -The purpose of this paper is to numerically study blood flow through a subject-specific carotid artery with a moderately severe stenosis, also to thoroughly analyse the wall shear stress (WSS), oscillatory shear index (OSI) and WSS angular deviation (WSSAD). One of the important aspects of this study is the investigation on the influence of the extensions attached to the domain outlets. Design/methodology/approach -The segmentation of the carotid artery is carried out using a deformable model based on a level set method. A geometric potential force (GPF) is employed to deform the level set to obtain the carotid artery geometry. The initial surface meshing is generated using an advanced marching cubes (MC) method, before improving the quality of the surface mesh via a number of mesh cosmetic steps. The volume mesh generation has two parts. In the first part, a quasi-structured, boundary layer mesh is generated in the vicinity of the geometry walls. The second part of the meshing involves unstructured tetrahedral meshing of the inner part of the geometry. After the meshing stage, the flow boundary conditions are generated by numerically solving the Helmholtz equation in both space and time. Finally, the explicit characteristic-based split (CBS) method is employed in a parallel environment to produce a detailed analysis of wall quantities. Findings -In general, WSS is very high in the vicinity of the carotid artery apex and in the proximity of the stenosis. From the results obtained, it is clear that the influence of outlet domain extension is marginal. While the peak instantaneous WSS differs by a maximum of 5.7 per cent, the time-averaged WSS difference due to extended domain is only 1.3 per cent. Two other derived parameters are also examined in the paper, the oscillating shear index and the WSSAD. Both these quantities also display minor or negligible differences due to domain extension. Originality/value -It has been perceived that domain extension is essential to avoid wrong application of boundary conditions. The results obtained, however, conclusively show that the outlet domain extension has only a moderate influence on WSS. Thus, outlet extension to the domains may not be essential for arterial blood flows. It is also observed that the dramatic values of peak WSS obtained near the stenosis is the result of high resolution mesh along with boundary layers used in this study. Both the outcomes represent the originality of this paper.