<p>The heart is a complex three-dimensional structure with mechanical properties that are inhomogeneous, non-linear, time-variant and anisotropic. These properties affect major physiological factors within the heart, such as the pumping performance of the ventricles, the oxygen demand in the tissue and the distribution of coronary blood flow.</p><p>During the cardiac cycle the heart muscle tissue is deformed as a consequence of the active contraction of the muscle fibers and their relaxation respectively. A mapping of this deformation would give increased understanding of the mechanical properties of the heart. The deformation induces strain and stress in the tissue which are both mechanical properties and can be described with a mathematical tensor object.</p><p>The aim of this master's thesis is to develop a visualization tool for the strain tensor objects that can aid a user to see and/or understand various differences between different hearts and spatial and temporal differences within the same heart. Preferably should the tool be general enough for use with different types of data.</p>

The heart is a complex three-dimensional structure with mechanical properties that are inhomogeneous, non-linear, time-variant and anisotropic. These properties affect major physiological factors within the heart, such as the pumping performance of the ventricles, the oxygen demand in the tissue and the distribution of coronary blood flow. During the cardiac cycle the heart muscle tissue is deformed as a consequence of the active contraction of the muscle fibers and their relaxation respectively. A mapping of this deformation would give increased understanding of the mechanical properties of the heart. The deformation induces strain and stress in the tissue which are both mechanical properties and can be described with a mathematical tensor object. The aim of this master's thesis is to develop a visualization tool for the strain tensor objects that can aid a user to see and/or understand various differences between different hearts and spatial and temporal differences within the same heart. Preferably should the tool be general enough for use with different types of data.

Pas de résumé disponible / The work done in this thesis is related to the project 3DStrain the overall objective of which is to develop a generic framework for the parietal and regional tracking of the left ventricle and to adapt it the 3D + t cardiac imaging modalities used in clinical routine (3D ultrasound, SPECT, cine MRI). We worked on the parietal motion and myocardial deformation. We made the state-of-the-art on motion estimation approaches in general and on methods applied to imaging modalities in clinical practice to quantify myocardial deformation taking into account their specificities and limitations. We focused on tracking methods that optimize the similarity between the intensities between consecutive images of a sequence to estimate the spatial velocity field. They are based on the assumption of the invariance of image gray level (or optical flow) and regularization terms are used to solve the aperture problem. We proposed a regularization term well suited to physical and physiological properties of myocardial motion. The advantage of the proposed approach relies on its flexibility to estimate the dense field of myocardial motion on image sequences over the cardiac cycle. Motion is estimated while preserving myocardial wall discontinuities. However, the data similarity term used in our method is based only on the intensity of the image. It properly estimates the displacement field especially in the radial direction as the movement of circumferential twist is hardly visible on cine MRI in short axis view, the data we used for performing the experiments. To make the estimation more robust, we proposed a dynamic evolution model for the cardiac contraction and relaxation to introduce the temporal constraint ofthe dynamics of the heart. This model helps to estimate not only the dense field of myocardial displacement, but also other parameters of myocardial contractility (the contraction phase and asymmetry between systole and diastole) in variational data assimilation formalism. Automatic estimation of deformation and myocardial contractibility (the strain, phase and asymmetry) was validated against the cardiological and radiological expertise (Dr Elisabeth Coupez and Dr Lucie Cassagnes, CHU Clermont-Ferrand) through semi-quantitative scores of contraction called Wall Motion Score (WMS) and Wall Thickening Index (WTI). The proposed method provides promising results for both motion estimation results and the diagnosis indices for evaluation of myocardial dyskinesia. In order to gain in robustness and accuracy, it is necessary to perform the measurement of strain and indices of myocardial contraction precisely inside endocardial and epicardial walls. Therefore, we conducted a collaborative work with Kevin Bianchi, another PhD student on the project 3DStrain and we proposed a method of coupling of myocardial segmentation by deformable models and estimation of myocardial motion in a variational data assimilation framework.

In recent times the potential impact of preeclampsia on the cardiovascular health of offspring has been identified. This thesis explores the relationship between preeclampsia and offspring cardiovascular phenotype during the first three decades of life. A systematic review and meta-analysis provided evidence that there was increased blood pressure and BMI in the offspring of preeclamptic pregnancies (n = 45,249). There was however limited data on metabolic features and inadequate characterisation of the degree of prematurity or growth restriction in existing literature. I therefore studied data on two birth cohorts with up to 28 years of detailed prospective follow up (n = 2868 and n = 926). Those born very preterm to preeclamptic pregnancies had transient perinatal reductions in insulin and cholesterol, although extreme prematurity was the only determinant of variation in cardiovascular risk in later life, with changes in both metabolism and blood pressure. In those born closer to, or at term, gestation was no longer relevant and an independent impact of preeclampsia on blood pressure was evident, so that by age 20, those born at term to preeclamptic pregnancies were four and a half times more likely to demonstrate clinically-apparent hypertension. I then investigated whether there were changes in other features of cardiovascular phenotype, independent of blood pressure, in preterm neonates born following preeclampsia (n = 46). At 3 months of age preterm infants born to hypertensive pregnancies had subclinical alterations in cardiac strain, independent of gestation or birth weight but not differences in blood pressure, or microvascular structure. These findings highlight preeclampsia and prematurity as key, independent perinatal factors, important in determining cardiovascular phenotype and risk during early life. Preeclampsia is associated with a specific lean, hypertensive phenotype, associated with cardiac functional alterations; these findings begin to define a distinct at risk population who may require targeted preventative interventions.