Improving cardiovascular imaging diagnostics by using patient-specific numerical simulations and biomechanical analysis

Overview

Ultrasound is the only imaging modality, apart from magnetic resonance imaging (MRI), that provides real-time functional and structural information on the beating heart. However, modeling moving cardiovascular structures is a complex process that requires three- dimensional (3D) reconstruction of two-dimensional (2D) data by fast imaging techniques (e.g., MRI) to thus yield dynamic four-dimensional (4D) views of cardiovascular pulsations. The unique 3D geometry of the cardiovascular system is partially responsible for the diversity of physiologic interactions between blood flow and cardiovascular structures. Recent advances in 3D echocardiography, cardiac computed tomography (CT), and MRI techniques have improved cardiovascular diagnostics considerably. In addition, with the advances achieved in graphics techniques for surface rendering, the potential for attaining useful information from graphics in medical imaging has emerged. Several techniques have been developed, such as the maximum intensity projection, shaded surface display, volumetric rendering, and others. The visualization tool kit (VTK) and the insight tool kit (ITK) are two examples of packages developed for performing image registration and segmentation based on ITK and VTK libraries. These open-source tool kits have an active development community that includes laboratories, institutions, and universities from around the world. ^,

Notably, with advanced 3D cardiovascular imaging techniques, complex intraventricular and intraaortic blood flow patterns can be partially evaluated. Even sophisticated 4D MRI cannot analyze all the fine details of the miscellaneous phenomena active in a 3D field of cardiovascular flow, which may be important in patients with subtle cardiac dysfunction, or evaluate the interactions between blood flow and vascular structures, which may be captured, for example, by models predicting the evolution of aortic disorders (e.g., predicting rupture of an abdominal aortic aneurysm [AAA]). These considerations have led to the development of numerical simulation models that provide functional imaging approaches to the investigation of blood flow patterns. These models are theoretic, which is a major limitation, and thus do not provide in-vivo data. However, the latter may be integrated into the boundaries used to run numerical simulations. This chapter outlines computational fluid dynamics (CFD) and fluid structure-interaction (FSI) models used in the study of cardiovascular flow phenomena in normal and aneurysmal aortas, respectively.