Computational FFR estimation in stable coronary artery disease with 1D and3Dmodels

Lucca, Alessia
Computational FFR estimation in stable coronary artery disease with 1D and3Dmodels
Tuesday 17th March 2020
Fraccarollo, L; Mueller, L.O.
Advisor II:
Vergara, C.
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Coronary artery disease (CAD) is one of the leading cause of death in the world[5]. CAD is caused by the buildup of atherosclerotic plaques in the coronary vessel wall, resulting in a reduction in oxygen supply to the hearth and a possibly leading to cardiovascular-related events such as myocardial infarction, stroke and unstable angina [28].Depending on the characteristics of the atherosclerotic lesions, several alter-native treatments exist for CAD. In this context, the currently gold standard for diagnosis of hemodynamic significance of coronary stenoses is the FractionalFlow Reserve (FFR). FFR is considered to be a specific index of the stenosis severity and it is assessed by invasive measurements of trans-stenotic pressure drops thanks to the insertion of a pressure guidewire across coronary stenosis during catheterization. The aim of our work is to estimate FFR non-invasively through the use of computer simulations of coronary blood flow and to evaluate the possible effects of the pressure guidewire on clinical pressure measurements. For this purpose,making use of valuable information regarding anatomy and vascular geometry contained in medical images, we compare results obtained via numerical simulations performed on two configurations: a stenotic coronary tree 3D model with and without pressure guidewire. The use of full three dimensional blood flow model based on incompressible Navier-Stokes equations implies several challenges, which range from lumen segmentation from Computed Tomography (CT) images and mesh generation to time-consuming numerical simulations. Thus, a simplified mathematical model, based on the 1D Navier-Stokes equations in compliant vessels, has been developed for exploring some modelling assumptions with a computationally less expensive tool and to obtain physiologically sound boundary conditions for the 3D model.The work is organized as follow.In Chapter 1 we describe the physiological features of the clinical problem. In particular we focus our attention on the coronary system and the pathological aspects of coronary artery disease.In Chapter 2 we translate the clinical problem into a mathematical one. Start-ing from the incompressible Navier-Stokes equations, we derive the 3D and 1D model for blood flow in coronary arteries. In turn, we describe the numerical approximation for both models, in particular we use a Finite Element Method in combination with a finite differences for time discretization for the 3D model,while a Finite Volume Method is used for the discretization of the 1D model.In Chapter 3 we observe the need of imposing reasonable boundary conditions and we describe two approaches to obtain them.In Chapter 4 we describe the physical and computational setting that we are going to use to perform 3D simulations, explaining the procedure to generate meshes with pressure guidewire inserted. In Chapter 5 we estimate all the parameters necessary for the computer simulations. Moreover, we present our numerical results together with their computational scenarios. In Chapter 6 we discuss our results, in particular we highlight the effects of the insertion of pressure guidewire across stenotic vessel on the estimation of FFR and we compare the diagnostic capability of 1D model with that of 3D model. In Chapter 7 we conclude our work by collecting our considerations on the results obtained and say something about future work.