Advances in the imaging techniques of the heart have fueled the interest in understanding of right heart pathology. Recently, speckle tracking echocardiography has shown to aid in understanding various right heart diseases and better management. Its role is well established in diagnosing right heart failure, pulmonary artery hypertension, arrhythmogenic right ventricular dysplasia and congenital heart disease. We review the basic mechanics of speckle tracking and analyze its role in various right heart conditions.

Posterior tibial tendon dysfunction (PTTD) is a common degenerative condition leading to a severe impairment of gait. There is currently no effective method to determine whether a patient with advanced PTTD would benefit from several months of bracing and physical therapy or ultimately require surgery. Tendon degeneration is closely associated with irreversible degradation of its collagen structure, leading to changes to its mechanical properties. If these properties could be monitored in vivo, it could be used to quantify the severity of tendonosis and help determine the appropriate treatment. Ultrasound elasticity imaging (UEI) is a real-time, noninvasive technique to objectively measure mechanical properties in soft tissue. It consists of acquiring a sequence of ultrasound frames and applying speckle tracking to estimate displacement and strain at each pixel. The goals of my dissertation were to 1) use acoustic simulations to investigate the performance of UEI during tendon deformation with different geometries; 2) develop and validate UEI as a potentially noninvasive technique for quantifying tendon mechanical properties in human cadaver experiments; 3) design a platform for UEI to measure mechanical properties of the PTT in vivo and determine whether there are detectable and quantifiable differences between healthy and diseased tendons. First, ultrasound simulations of tendon deformation were performed using an acoustic modeling program. The effects of different tendon geometries (cylinder and curved cylinder) on the performance of UEI were investigated. Modeling results indicated that UEI accurately estimated the strain in the cylinder geometry, but underestimated in the curved cylinder. The simulation also predicted that the out-of-the-plane motion of the PTT would cause a non-uniform strain pattern within incompressible homogeneous isotropic material. However, to average within a small region of interest determined by principal component analysis (PCA) would improve the estimation. Next, UEI was performed on five human cadaver feet mounted in a materials testing system (MTS) while the PTT was attached to a force actuator. A portable ultrasound scanner collected 2D data during loading cycles. Young's modulus was calculated from the strain, loading force and cross sectional area of the PTT. Average Young's modulus for the five tendons was (0.45±0.16GPa) using UEI. This was consistent with simultaneous measurements made by the MTS across the whole tendon (0.52±0.18GPa). We also calculated the scaling factor (0.12±0.01) between the load on the PTT and the inversion force at the forefoot, a measurable quantity in vivo. This study suggests that UEI could be a reliable in vivo technique for estimating the mechanical properties of the human PTT. Finally, we built a custom ankle inversion platform for in vivo imaging of human subjects (eight healthy volunteers and nine advanced PTTD patients). We found non-linear elastic properties of the PTTD, which could be quantified by the slope between the elastic modulus (E) and the inversion force (F). This slope (ΔE/ΔF), or Non-linear Elasticity Parameter (NEP), was significantly different for the two groups: 0.16±0.20 MPa/N for healthy tendons and 0.45±0.43 MPa/N for PTTD tendons. A receiver operating characteristic (ROC) curve revealed an area under the curve (AUC) of 0.83±0.07, which indicated that the classifier system is valid. In summary, the acoustic modeling, cadaveric studies, and in vivo experiments together demonstrated that UEI accurately quantifies tendon mechanical properties. As a valuable clinical tool, UEI also has the potential to help guide treatment decisions for advanced PTTD and other tendinopathies.

Speckle tracking echocardiography (STE) is a relatively new imaging modality that enables the direct measurement of active contractile myocardial tissue in an offline analysis. This is accomplished through a software algorithm that tracks collections of acoustic markers, known as 'speckles', that are unique to a given section of myocardium. By measuring the displacement of these 'speckles' as the heart contracts and relaxes, STE produces parameters of the strain, or percent change in length, exhibited by the myocardium. As multiple studies have shown, this strain data produced by tracking of the global left atrium has the ability to accurately assess the physiologic functions of the atrium as a reservoir, conduit and booster pump in the cardiac cycle. Despite these valuable correlations, there are noted problems with STE regarding acoustic cluttering and disappearance of 'speckles' that can occur as the selected region of interest moves out of the field of view or becomes obscured. These problems may be increased when tracking an extended region of myocardium. Therefore, this present study sought to test a new method of assessing left atrial function with STE strain analysis by focusing on a concise region of the atrium, specifically the interatrial septum. To test this, the echocardiograms of 37 patients were obtained and grouped according to the designation of their cardiac function as normal (n=11), abnormal (n=12), or exhibiting signs of cardiac amyloidosis (n=14). In all patients, STE strain analysis was performed on the both the global left atrium and the interatrial septum. Measurements of the mean peak strain observed in the resultant strain curves were recorded for both STE scans of each patient. The curves produced by the tracking the segments of the entire atrium (6 segments) and interatrial septum (3 segments) were compared based on the exhibited changes in strain seen in the relative shapes of the curves, as well as the spread of the segmental strain curves about the calculated mean strain curve. Additionally, the number of segments that were either unsuccessfully or incorrectly tracked was recorded as a measure of the accuracy of STE. As a final step, the interatrial strain curves of four selected patients in the various states of ventricular diastolic dysfunction were chosen and compared with data obtained from scans of mitral flow echocardiography and tissue Doppler imaging (TDI) in an attempt to correlate the exhibited changes in strain shown in the interatrial septum with the physiologic functions of the atrium during ventricular diastole. The results showed that the mean peak strain of the global atrial strain trace decreased from normal (41.32%±10.8) to abnormal (21.69%±13.8) to the amyloid group (10.41%±6.9). This trend was echoed in the mean peak strain measured in the interatrial septum, as measured in normal (64.2%±15.6), abnormal (28.37%±13.4) and amyloid groups (12.21%±12.1). When the strain curves of the entire atrium and interatrial septum were compared, they demonstrated similar patterns in the timing of changes in strain, however the strain curves of the individual interatrial septum segments showed a much more concise grouping about the mean strain curve and were less likely to exhibit discordant segmental strain curves that deviated from the pattern established by all other segments in the trace. Additionally, within the STE scans of the global atrium, the interatrial septum exhibited a higher percentage of successfully tracked segments than did the lateral atrial wall; this trend was universally exhibited in all three groups. Finally, the interatrial septum strain curves, mitral flow echocardiography and TDI scans all demonstrated similar indications of left atrial function in the four selected patients. Ultimately, STE strain analysis of the interatrial septum appears to be a more accurate method of tracking the atrial myocardium than STE tracing of the global left atrium. Furthermore, it shows viable potential as a method for assessing the global physiologic function of the left atrium, as indicated by the similarities between the trends exhibited by these STE scans and the data gathered from scans produced by mitral flow echocardiography and TDI.

L’objectif de cette thèse est d'étudier le ventricule droit (VD) dans différentes conditions de charge en utilisant imagerie et modélisation. Le premier axe de ce travail est une étude prospective qui analyse la déformation VD chez des patients sains et avec hypertension pulmonaire (HTP) en utilisant l’échocardiographie trans-thoracique 3D. Les maillages VD ont été obtenus par tracking myocardique et post-traités afin d’extraire le strain de surface. Les correspondances spatiotemporelles ont été vérifiées avant de réaliser les statistiques des maillages. La forme et déformation globale VD sont associées à la sévérité de l'HTP et donnent des informations pronostiques. Le deuxième axe de ce travail présente le rôle d'une évaluation longitudinale par rapport à celui d’une évaluation instantanée, en utilisant la même méthodologie. Nous avons démontré la valeur ajoutée pronostique des modifications dans le temps de déformation VD et l'importance du septum. Dans le troisième axe, les aspects complémentaires de la forme (définie par la courbure) et déformation VD ont été évalués dans des populations de surcharge en volume VD. Alors que forme et déformation sont altérés chez les patients avec tétralogie de Fallot, seule la forme a permis de différencier les patients avec CIA des témoins. Enfin, dans le dernier axe, nous avons étudié la valeur ajoutée de la personnalisation d'un modèle circulatoire 0D pour caractériser la pathologie et prédire la réponse au traitement dans l’hypertension artérielle pulmonaire. Le modèle a été personnalisé pour 11 patients avant et après traitement spécifique de l’HTP. Les paramètres du modèle reflètent bien les changements attendus avec la thérapie. / The aim of this thesis is to study the right ventricle (RV) in different loading conditions using imaging and modelling. The first axis of this work was a prospective study in which we studied RV deformation in healthy controls and pulmonary hypertension (PH) patients (pressure overload) using 3D transthoracic RV echocardiographic sequences. Output RV meshes; obtained after myocardial tracking; were post-processed to extract area strain and spatiotemporal correspondences were checked before computing statistics on these meshes. RV shape and strain patterns were gradually deteriorated with the severity of PH and provided independent prognostic information. The second axis of this work focused on the role of a longitudinal evaluation in comparison with a single assessment at baseline, using the same methodology. We demonstrated the additional prognostic value of changes in RV area strain and the importance of septal segments. In the third axis, we assessed the complementary aspects of RV deformation and shape (using curvature index) in RV volume overload patients. While shape and strain are both altered in tetralogy of Fallot patients, only RV shape allows to differentiate atrial septal defects from normal controls. Finally, in the last axis, we focused on the added value of the personalisation of a 0D circulation model to characterize the pathology and predict the response to therapy in pulmonary arterial hypertension. The model was personalised to 11 PH patient data before and after advanced specific PH therapy. The model parameters reflected accurately the expected changes with therapy.