Invasive and Non-Invasive Quantification of Cardiac Kinematics

Sammanfattning: The ability to measure and quantify myocardial motion and deformation provides a useful tool to assist in the diagnosis, prognosis and management of heart disease. Myocardial motion can be measured by means of several different types of data acquisition. The earliest myocardial motion tracking technique was invasive, based on implanting radiopaque markers into the myocardium around the left ventricle, and recording the marker positions during the cardiac cycle by biplane cineradiography. Until recently, this was the only method with high enough spatial resolution of three-dimensional (3D) myocardial displacements to resolve transmural behaviors. However, the recent development of magnetic resonance imaging techniques, such as displacement encoding with stimulated echoes (DENSE), make detailed non-invasive 3D transmural kinematic analyses of human myocardium possible in the clinic and for research purposes.Diastolic left ventricular filling is a highly dynamic process with early and late transmitral inflows and it is determined by a complex sequence of many interrelated events and parameters. Extensive research has been performed to describe myocardial kinematics during the systolic phase of the cardiac cycle, but not by far the same amount of research has been accomplished during diastole. Measures of global and regional left ventricular kinematics during diastole are important when attempting to understand left ventricular filling characteristics in health and disease.This thesis presents methods for invasive and non-invasive quantification of cardiac kinematics, with focus on diastole. The project started by quantification of changes in global left ventricular kinematics during diastolic filling. The helical myocardial fiber architecture of the left ventricle produces both long- and short-axis motion as well as torsional deformation. The longitudinal excursion of the mitral annular plane is an important component of left ventricular filling and ejection. This was studied by analyzing the contribution of mitral annular dynamics to left ventricular filling volume in the ovine heart.In order to quantify strains for a specific body undergoing deformation, displacements for a set of internal points at a deformed configuration relative to a reference configuration are needed. A new method for strain quantification from measured myocardial displacements is presented in this thesis. The method is accurate and robust and delivers analytical expressions of the strain components. The developed strain quantification method is simple in nature which aids to bridge a possible gap in understanding between different disciplines and is well suited for sparse arrays of displacement data.Analyses of myocardial kinematics at the level of myocardial fibers require knowledge of cardiac tissue architecture. Temporal changes in myofiber directions during the cardiac cycle have been analyzed in the ovine heart by combining histological measurements of transmural myocardial architecture and local transmural strains.Rapid early diastolic filling is an essential component of the left ventricular function. Such filling requires a highly compliant chamber immediately after systole, allowing inflow at low driving pressures. Failure of this process can lead to exercise intolerance and ultimately to heart failure. A thorough analysis of the relation between global left ventricular kinematics and local myocardial strain at the level of myocardial fibers during early diastole in the ovine heart was performed by applying the method for strain quantification and the technique for computing temporal changes in myocardial architecture on measures of myocardial displacements and tissue architecture in the ovine heart.As data acquisition technologies develop, quantification methods for cardiac kinematics need to be adapted and validated on the new types of data. Recent improvements of DENSE magnetic resonance imaging enable non-invasive transmural strain analyses in the human heart. The strain quantification method was first tailored to displacement data from a surgically implanted bead array but has been extended to applications on non-invasive DENSE data measured in two and three dimensions. Validation against an analytical standard reveals accurate results and in vivo strains agree with values for normal human hearts from other studies.The method has in this thesis been used with displacement data from invasive marker technology and non-invasive DENSE magnetic resonance imaging, but can equally well be applied on any type of displacement data provided that the spatial resolution is high enough to resolve local strain variations.