Thesis (doctoral)--Ludwig Maximilians-Universität zu München, 1979.

Thesis (MScEng)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Le but de cette étude est d’évaluer la faisabilité de l’analyse tomodensitométrique 3D des bioprothèses aortiques pour faciliter leur évaluation morphologique durant le suivi et d’aider la sélection de cas et améliorer la planification d’une procédure valvein-valve. Le challenge était représenté par le rehaussement des feuillets valvulaires, en raison d’images très bruitées. Un angio-scanner synchronisé était réalisé chez des patients porteurs d’une bioprotèses aortique dégénérée avant réintervention (images in-vivo). Différentes méthodes pour la réduction du bruit étaient proposées. La reconstruction tridimensionnelle des bioprothèses était réalisée en utilisant des méthodes de segmentation de régions par "sticks". Après réopération ces méthodes étaient appliquées aux images scanner des bioprothèses explantées (images ex-vivo) et utilisées comme référence. La réduction du bruit obtenue par le filtre stick modifié montrait meilleurs résultats en rapport signal/bruit en comparaison aux filtres de diffusion anisotropique. Toutes les méthodes de segmentation ont permis une reconstruction 3D des feuillets. L’analyse qualitative a montré une bonne concordance entre les images obtenues in-vivo et les altérations des bioprothèses. Les résultats des différentes méthodes étaient comparés par critères volumétriques et discutés. Les bases d'une première approche de visualisation spatio-temporelle d'images TDM 3D+T de la prothèse valvulaire ont été proposés. Elle implique des techniques de rendu volumique et de compensation de mouvement. Son application à la valve native a aussi été envisagée. Les images scanner des bioprothèses aortiques nécessitent un traitement de débruitage et de réduction des artéfacts de façon à permettre le rehaussement des feuillets prothétiques. Les méthodes basées sticks semblent constituer une approche pertinente pour caractériser morphologiquement la dégénérescence des bioprothèses. / The aim of the study was to assess the feasibility of CT based 3D analysis of degenerated aortic bioprostheses to make easier their morphological assessment. This could be helpful during regular follow-up and for case selection, improved planning and mapping of valve-in-valve procedure. The challenge was represented by leaflets enhancement because of highly noised CT images. Contrast-enhanced ECG-gated CT scan was performed in patients with degenerated aortic bioprostheses before reoperation (in-vivo images). Different methods for noise reduction were tested and proposed. 3D reconstruction of bioprostheses components was achieved using stick based region segmentation methods. After reoperation, segmentation methods were applied to CT images of the explanted prostheses (exvivo images). Noise reduction obtained by improved stick filter showed best results in terms of signal to noise ratio comparing to anisotropic diffusion filters. All segmentation methods applied to the best phase of in-vivo images allowed 3D bioprosthetic leaflets reconstruction. Explanted bioprostheses CT images were also processed and used as reference. Qualitative analysis revealed a good concordance between the in-vivo images and the bioprostheses alterations. Results from different methods were compared by means of volumetric criteria and discussed. A first approach for spatiotemporal visualization of 3D+T images of valve bioprosthesis has been proposed. Volume rendering and motion compensation techniques were applied to visualize different phases of CT data. Native valve was also considered. ECG-gated CT images of aortic bioprostheses need a preprocessing to reduce noise and artifacts in order to enhance prosthetic leaflets. Stick based methods seems to provide an interesting approach for the morphological characterization of degenerated bioprostheses.

Diss. (sammanfattning) Stockholm : Karol. inst., 2002. / Härtill 6 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2006. / Härtill 4 uppsatser.

Electro-hydraulic proportional flow valves are widely used in hydraulic industry. There are several different structures and working principles. However, flow valves based on the existing principles usually have some shortcomings such as the complexity of the system and additional energy losses. A concept for a two-stage poppet flow valve with pilot pressure drop – pilot spool opening compensation is presented, and the linear relationship between the pilot stage and main stage, the semi-empirical flow equation are used in the electronic flow controller. To achieve the accurate control of the outlet flow, the actual input voltage of the pilot spool valve is regulated according to the actual pilot pressure drop, the desired flow rate and the given input voltage. The results show that the pilot pressure drop – pilot spool opening compensation method is feasible, and the proposed proportional flow control valve with this compensation method has a good static and dynamic performance.

Transcatheter aortic valve replacement in the setting of failed surgical bioprosthesis (valve-in-valve) is a valuable option for patients with bioprosthetic aortic stenosis or regurgitation who are deemed high risk for repeat open heart surgery. Although the procedure is successful with proper preprocedural assessment, instances of left main (LM) coronary artery ostium obstruction have been documented. We present a case of LM coronary obstruction in the immediate postoperative period following implantation of a 20-mm Edwards Sapien 3 valve inside the degenerated 21-mm Mitroflow bioprosthesis stenosis, which was treated with double stenting alongside the Edwards Sapien 3 valve creating a channel (“neo left main”) that extended from mid-LM to the upper margin of the Edwards Sapien 3 valve. Although valve-in-valve in a Mitroflow degenerated bioprosthesis is a relatively safe procedure, 2 or more stents may be necessary to scaffold a channel to the coronary arteries between Edwards Sapien 3 prosthesis and aorta in the event of a coronary obstruction.

In the heart, unidirectional blood flow depends on proper heart valve function. As, in mammals, regulatory mechanisms of early heart valve and bone development are shown to contribute to adult heart valve pathologies, we used the animal model zebrafish (ZF, Danio rerio) to investigate the microarchitecture and differentiation of cardiac valve interstitial cells in the transition from juvenile (35 days) to end of adult breeding (2.5 years) stages. Of note, light microscopy and immunohistochemistry revealed major differences in ZF heart valve microarchitecture when compared with adult mice. We demonstrate evidence for rather chondrogenic features of valvular interstitial cells by histological staining and immunodetection of SOX-9, aggrecan, and type 2a1 collagen. Collagen depositions are enriched in a thin layer at the atrial aspect of atrioventricular valves and the ventricular aspect of bulboventricular valves, respectively. At the ultrastructural level, the collagen fibrils are lacking obvious periodicity and orientation throughout the entire valve. (J Histochem Cytochem 67:361–373, 2019)

L’implantation valvulaire aortique percutanée (TAVI) a émergé comme une alternative à la chirurgie pour les patients avec sténose sévère et haut risque chirurgical. Cette technique s’étend à une population plus large (e.g. anatomie plus complexe, risque chirurgical plus bas), ainsi qu'au traitement Valve-in-Valve (ViV) des bioprothèses (BPs) chirurgicales défaillantes. Cependant, deux complications majeures en limitent la généralisation. En TAVI « classique », la présence de fuites péripothétiques a été associée à une mortalité augmentée. Les effets du surdimensionnement de la prothèse percutanée pour assurer son étanchéité, ou de la forme de l’anneau souvent non circulaire, sur la performance hémodynamique, sont mal connus. En ViV, la présence de hauts gradients est fréquente et associée à une mortalité augmentée. Les BPs de taille nominale ≤ 21 mm et le mode de dégénérescence par sténose, facteurs mis en cause dans la sténose résiduelle et associés à une mortalité augmentée, ne sont pas assez spécifiques et il n’existe actuellement aucune recommandation pour le traitement des petites BPs. Par ailleurs, le bénéfice hémodynamique réel du ViV par rapport aux statuts avant ViV n’a pas été étudié.L’objectif général de ce travail doctoral est de comprendre les interactions entre la prothèse percutanée et l’anneau aortique ou la BP à traiter, impliquées dans la performance hémodynamique, en particulier dans des conditions d’implantation complexes, afin d’étendre les indications du TAVI. En ViV, le défi est de préciser les facteurs associés à sa performance et son utilité hémodynamique et de proposer des stratégies d’implantation afin d’optimiser le succès de la procédure. / Transcatheter aortic valve implantation (TAVI) has emerged as an alternative to surgery for patients with severe aortic stenosis and high surgical risk. This technique is extending to a wider population (e.g. with more complex anatomy or lower surgical risk), as well as to patients with degenerated surgical bioprostheses (BPs). However, two major concerns remain limiting. Regarding “classical TAVI”, periprosthetic leaks have been associated with increased mortality. Oversizing is used to secure the device within the aortic annulus which is often non circular. The effects of oversizing and annulus shape on the hemodynamic performance are unknown. Regarding ViV implantations, elevated post-procedural gradients are common and have been associated with increased mortality. The principal factors associated with this residual stenosis as well as with increased risk of mortality, have been BPs label size ≤ 21 mm and mode of failure by stenosis. These factors are not specific enough and there is currently no recommendation for the treatment of small BPs. Besides, the actual hemodynamic benefit associated with ViV has not been evaluated (vs. pre ViV status).The general objective of this work is to understand the interactions between the transcatheter prosthesis and the aortic annulus or the BP to be treated, which impact the hemodynamic performance, especially in complex conditions of implantation, in order to extend the indications of TAVI. In the context of ViV, the objective is to specify the factors associated with the hemodynamic performance and utility of the treatment. The final aim is to provide strategies of implantation in order to optimize the success of the procedure.

The aim of the study was to assess the feasibility of CT based 3D analysis of degenerated aortic bioprostheses to make easier their morphological assessment. This could be helpful during regular follow-up and for case selection, improved planning and mapping of valve-in-valve procedure. The challenge was represented by leaflets enhancement because of highly noised CT images. Contrast-enhanced ECG-gated CT scan was performed in patients with degenerated aortic bioprostheses before reoperation (in-vivo images). Different methods for noise reduction were tested and proposed. 3D reconstruction of bioprostheses components was achieved using stick based region segmentation methods. After reoperation, segmentation methods were applied to CT images of the explanted prostheses (exvivo images). Noise reduction obtained by improved stick filter showed best results in terms of signal to noise ratio comparing to anisotropic diffusion filters. All segmentation methods applied to the best phase of in-vivo images allowed 3D bioprosthetic leaflets reconstruction. Explanted bioprostheses CT images were also processed and used as reference. Qualitative analysis revealed a good concordance between the in-vivo images and the bioprostheses alterations. Results from different methods were compared by means of volumetric criteria and discussed. A first approach for spatiotemporal visualization of 3D+T images of valve bioprosthesis has been proposed. Volume rendering and motion compensation techniques were applied to visualize different phases of CT data. Native valve was also considered. ECG-gated CT images of aortic bioprostheses need a preprocessing to reduce noise and artifacts in order to enhance prosthetic leaflets. Stick based methods seems to provide an interesting approach for the morphological characterization of degenerated bioprostheses.