Development of a Surgical Assistance System for Guiding Transcatheter Aortic Valve Implantation

Development of image-guided interventional systems is growing up rapidly in the recent years. These new systems become an essential part of the modern minimally invasive surgical procedures, especially for the cardiac surgery. Transcatheter aortic valve implantation (TAVI) is a recently developed surgical technique to treat severe aortic valve stenosis in elderly and high-risk patients. The placement of stented aortic valve prosthesis is crucial and typically performed under live 2D fluoroscopy guidance. To assist the placement of the prosthesis during the surgical procedure, a new fluoroscopy-based TAVI assistance system has been developed. The developed assistance system integrates a 3D geometrical aortic mesh model and anatomical valve landmarks with live 2D fluoroscopic images. The 3D aortic mesh model and landmarks are reconstructed from interventional angiographic and fluoroscopic C-arm CT system, and a target area of valve implantation is automatically estimated using these aortic mesh models. Based on template-based tracking approach, the overlay of visualized 3D aortic mesh model, landmarks and target area of implantation onto fluoroscopic images is updated by approximating the aortic root motion from a pigtail catheter motion without contrast agent. A rigid intensity-based registration method is also used to track continuously the aortic root motion in the presence of contrast agent. Moreover, the aortic valve prosthesis is tracked in fluoroscopic images to guide the surgeon to perform the appropriate placement of prosthesis into the estimated target area of implantation. An interactive graphical user interface for the surgeon is developed to initialize the system algorithms, control the visualization view of the guidance results, and correct manually overlay errors if needed. Retrospective experiments were carried out on several patient datasets from the clinical routine of the TAVI in a hybrid operating room. The maximum displacement errors were small for both the dynamic overlay of aortic mesh models and tracking the prosthesis, and within the clinically accepted ranges. High success rates of the developed assistance system were obtained for all tested patient datasets. The results show that the developed surgical assistance system provides a helpful tool for the surgeon by automatically defining the desired placement position of the prosthesis during the surgical procedure of the TAVI.Die Entwicklung bildgeführter interventioneller Systeme wächst rasant in den letzten Jahren. Diese neuen Systeme werden zunehmend ein wesentlicher Bestandteil der technischen Ausstattung bei modernen minimal-invasiven chirurgischen Eingriffen. Diese Entwicklung gilt besonders für die Herzchirurgie. Transkatheter Aortenklappen-Implantation (TAKI) ist eine neue entwickelte Operationstechnik zur Behandlung der schweren Aortenklappen-Stenose bei alten und Hochrisiko-Patienten. Die Platzierung der Aortenklappenprothese ist entscheidend und wird in der Regel unter live-2D-fluoroskopischen Bildgebung durchgeführt. Zur Unterstützung der Platzierung der Prothese während des chirurgischen Eingriffs wurde in dieser Arbeit ein neues Fluoroskopie-basiertes TAKI Assistenzsystem entwickelt. Das entwickelte Assistenzsystem überlagert eine 3D-Geometrie des Aorten-Netzmodells und anatomischen Landmarken auf live-2D-fluoroskopische Bilder. Das 3D-Aorten-Netzmodell und die Landmarken werden auf Basis der interventionellen Angiographie und Fluoroskopie mittels eines C-Arm-CT-Systems rekonstruiert. Unter Verwendung dieser Aorten-Netzmodelle wird das Zielgebiet der Klappen-Implantation automatisch geschätzt. Mit Hilfe eines auf Template Matching basierenden Tracking-Ansatzes wird die Überlagerung des visualisierten 3D-Aorten-Netzmodells, der berechneten Landmarken und der Zielbereich der Implantation auf fluoroskopischen Bildern korrekt überlagert. Eine kompensation der Aortenwurzelbewegung erfolgt durch Bewegungsverfolgung eines Pigtail-Katheters in Bildsequenzen ohne Kontrastmittel. Eine starrere Intensitätsbasierte Registrierungsmethode wurde verwendet, um kontinuierlich die Aortenwurzelbewegung in Bildsequenzen mit Kontrastmittelgabe zu detektieren. Die Aortenklappenprothese wird in die fluoroskopischen Bilder eingeblendet und dient dem Chirurg als Leitfaden für die richtige Platzierung der realen Prothese. Eine interaktive Benutzerschnittstelle für den Chirurg wurde zur Initialisierung der Systemsalgorithmen, zur Steuerung der Visualisierung und für manuelle Korrektur eventueller Überlagerungsfehler entwickelt. Retrospektive Experimente wurden an mehreren Patienten-Datensätze aus der klinischen Routine der TAKI in einem Hybrid-OP durchgeführt. Hohe Erfolgsraten des entwickelten Assistenzsystems wurden für alle getesteten Patienten-Datensätze erzielt. Die Ergebnisse zeigen, dass das entwickelte chirurgische Assistenzsystem ein hilfreiches Werkzeug für den Chirurg bei der Platzierung Position der Prothese während des chirurgischen Eingriffs der TAKI bietet

Dynamic Analysis of X-ray Angiography for Image-Guided Coronary Interventions

Percutaneous coronary intervention (PCI) is a minimally-invasive procedure for treating patients with coronary artery disease. PCI is typically performed with image guidance using X-ray angiograms (XA) in which coronary arter

Improved Image Guidance in TACE Procedures

Purpose of the work in this thesis is to improve the image guidance in TACE procedures. More specifically, we intend to develop and evaluate technology that permits dynamic roadmapping based on a 3D model of the liver vasculature

Exploiting Temporal Image Information in Minimally Invasive Surgery

Minimally invasive procedures rely on medical imaging instead of the surgeons direct vision. While preoperative images can be used for surgical planning and navigation, once the surgeon arrives at the target site real-time intraoperative imaging is needed. However, acquiring and interpreting these images can be challenging and much of the rich temporal information present in these images is not visible. The goal of this thesis is to improve image guidance for minimally invasive surgery in two main areas. First, by showing how high-quality ultrasound video can be obtained by integrating an ultrasound transducer directly into delivery devices for beating heart valve surgery. Secondly, by extracting hidden temporal information through video processing methods to help the surgeon localize important anatomical structures. Prototypes of delivery tools, with integrated ultrasound imaging, were developed for both transcatheter aortic valve implantation and mitral valve repair. These tools provided an on-site view that shows the tool-tissue interactions during valve repair. Additionally, augmented reality environments were used to add more anatomical context that aids in navigation and in interpreting the on-site video. Other procedures can be improved by extracting hidden temporal information from the intraoperative video. In ultrasound guided epidural injections, dural pulsation provides a cue in finding a clear trajectory to the epidural space. By processing the video using extended Kalman filtering, subtle pulsations were automatically detected and visualized in real-time. A statistical framework for analyzing periodicity was developed based on dynamic linear modelling. In addition to detecting dural pulsation in lumbar spine ultrasound, this approach was used to image tissue perfusion in natural video and generate ventilation maps from free-breathing magnetic resonance imaging. A second statistical method, based on spectral analysis of pixel intensity values, allowed blood flow to be detected directly from high-frequency B-mode ultrasound video. Finally, pulsatile cues in endoscopic video were enhanced through Eulerian video magnification to help localize critical vasculature. This approach shows particular promise in identifying the basilar artery in endoscopic third ventriculostomy and the prostatic artery in nerve-sparing prostatectomy. A real-time implementation was developed which processed full-resolution stereoscopic video on the da Vinci Surgical System

Magnetic navigation in percutaneous coronary and non-coronary interventions

There is no question that Percutaneous Coronary Intervention has revolutionized the way we manage coronary artery disease. Over the past two decades we have witnessed maturity in several techniques and equipment enabling the interventional cardiologist to manage lesions that have previously been entirely in the domain of the cardiac surgeon. Despite these remarkable achievements there still remain lesions that are complex enough to create a challenge in the most experienced hands.The inherent tortuosity in complex vascular anatomies, branching segments and chronically occluded vessel have been all associated with lower procedural success and higher complication rates when compared to the “straight forward vessels”. The Magnetic Navigation System (MNS) is a novel and versatile technology that allows the re-orientation of a wire within the patient’s body. This unique ability means that the “trial and error” method of externally re-shaping the tip of the wire and re-engaging the vessel can be effectively eliminated. As such previously “unreachable areas” in the heart or within the vascul

Magnetic Navigation in Percutaneous Cardiac Intervention

Magnetic navigation is the use of a magnetic fi eld to re-orientate a magnetically-enabled wire or device. The fi eld is directed by external magnets that are moved by a computercontrolled system. This technology could improve percutaneous coronary interventional procedures as it improves 3 specifi c and complementary capabilities, namely precise tip adjustability, computer-enhanced, image-guided tip orientation, and computer–enhanced image processing. Although this technology is relatively new, it already appears that this system can equal, and even improve on, current conventional wire technique. The current usability, combined with the exciting potential of future developments, could result in a formidable adjunct to PCI. This thesis deals with the early use of the system, development of diff erent strategies for the exploitation of the unique novel features that the system has. Specifi cally it will describe a number of areas. 1. Background, history and system description: The aim of this introduction is to provide a brief description of the background of magnetic procedures with respect to Stereotaxis Inc, and a description of the magnetic moment, and a short description of the current system together with the specially-produced wires. 2. Feasibility in phantom models, and initial system development: This section deals with aspects related to feasibility of use, validation of the software, and initial experience in diff erent clinical situations and fi nally with the potential use in treating one of the sequelae of coronary disease i.e. poor left ventricular function by the possible delivery of cardiac stem cells. 3. Initial experience in clinical practice and illustrative case reports: This section deals with the clinical use in percutaneous coronary intervention concentrating on the initial patient studies. 4. Investigation of benefi ts in subgroups: This section concentrates on particular subsets of coronary intervention patients and the specifi c hypotheses that can be drawn from these

Apport de l'assistance par ordinateur lors de la pose d'endoprothèse aortique

The development of endovascular aortic procedures is growing. These mini-invasive techniques allow a reduction of surgical trauma, usually important in conventional open surgery. The technical limitations of endovascular repair are pushed to special aortic localizations which were in the past decade indication for open repair. Success and efficiency of such procedures are based on the development and the implementation of decision-making tools. This work aims to improve endovascular procedures thanks to a better utilization of pre and intraoperative imaging. This approach is in the line with the framework of computer-assisted surgery whose concepts are applied to vascular surgery. The optimization of endograft deployment is considered in three steps. The first part is dedicated to preoperative imaging analysis and shows the limits of the current sizing tools. The accuracy of a new measurement criterion is assessed (outer curvature length). The second part deals with intraoperative imaging and shows the contribution of augmented reality in endovascular aortic repair. In the last part, image guided surgery on soft tissues is addressed, especially the arterial deformations occurring during endovascular procedures which disprove rigid registration in fusion imaging. The use of finite element simulation to deal with this issue is presented. We report an original approach based on a predictive model of deformations using finite element simulation with geometrical and anatomo-mechanical patient specific parameters extracted from the preoperative CT-scan.Les techniques endovasculaires, particulièrement pour l’aorte, sont en plein essor en chirurgie vasculaire. Ces techniques mini-invasives permettent de diminuer l’agression chirurgicale habituellement importante lors de la chirurgie conventionnelle. Les limites techniques sont repoussées à certaines localisations de l’aorte qui étaient il y a encore peu de temps inaccessibles aux endoprothèses. Le succès et l’efficience de ces interventions reposent en partie sur l'élaboration et la mise en œuvre de nouveaux outils d'aide à la décision. Ce travail entend contribuer à l’amélioration des procédures interventionnelles aortiques grâce à une meilleure exploitation de l’imagerie pré et peropératoire. Cette démarche s’inscrit dans le cadre plus général des Gestes Médico-Chirurgicaux Assistés par Ordinateur, dont les concepts sont revisités pour les transposer au domaine de la chirurgie endovasculaire. Trois axes sont développés afin de sécuriser et optimiser la pose d'endoprothèse. Le premier est focalisé sur l’analyse préopératoire du scanner (sizing) et montre les limites des outils de mesure actuels et évalue la précision d’un nouveau critère de mesure des longueurs de l’aorte (courbure externe). Le deuxième axe se positionne sur le versant peropératoire et montre la contribution de la réalité augmentée dans la pose d’une endoprothèse aortique. Le troisième axe s’intéresse au problème plus général des interventions sur les tissus mous et particulièrement aux déformations artérielles qui surviennent au cours des procédures interventionnelles qui mettent en défaut le recalage rigide lors de la fusion d’images. Nous présentons une approche originale basée sur un modèle numérique de prédiction des déformations qui utilise la simulation par éléments finis en y intégrant des paramètres géométriques et anatomo-mécaniques spécifique-patient extraits du scanner préopératoire

Stem cell therapy for myocardial infarction

Coronary heart disease and heart failure continue to be significant burdens to healthcare systems in the Western world and are predicted to become so in emerging economies. Despite mixed results in both experimental and clinical studies, stem cell therapy is a promising option for patients suffering from myocardial infarction or patients with chronic heart failure after myocardial infarction. However, many issues in the field of cellular cardiomyoplasty still need to be resolved. This thesis describes the experiments performed in a pre-clinical model in swine with reperfused myocardial infarction aiming at addressing several of these issues. Chapter two of this thesis shows that infarct size in swine can be measured accurately with multislice computed tomography, as compared to the “golden standard” histology. This study showed that myocardial viability can be assessed with multislice computed tomography. Furthermore, since we used magnetic resonance imaging in chapter three and four, we showed that for purposes of infarct size assessment multislice computed tomography compares well with magnetic resonance imaging, which is described in chapter three. Measurement of infarct size in patients with acute myocardial infarction is clinically relevant because infarct size is predictive of left ventricular function and geometric configuration and, hence, long-term clinical outcome. Information on infarct size obtained with multislice computed tomography would enhance the diagnostic armamentarium of physicians who lack access to cardiac magnetic resonance imaging or encounter patients who have contra indications to undergo magnetic resonance imaging. The review of umbilical cord blood derived cells in the fourth chapter of this thesis shows a great potential of these cells to regenerate damaged myocardium. These cells can easily be obtained in large numbers and are not harvested from diseased individuals, therefore they have a great differentiation and proliferation capacity. Moreover, they do not raise ethical difficulties question, as do embryonic stem cells. In chapter five, the effect of umbilical cord blood cells is assessed with magnetic resonance imaging in a porcine model of myocardial infarction. There was no positive effect on left ventricular function or infarct size four weeks after injection of intracoronary administration of the umbilical cord blood cells, which what not very surprising since only a few of the injected cells survived. Therefore, the immunogenic status of these cells is not fully understood yet. However, this study shows that cultured umbilical cord blood cells should be used with caution when applied intracoronary, since their large cell size result in occluded blood vessels, thereby causing micro infarctions. Hence, it cannot be excluded that a possible positive effect of the umbilical cord blood derived cells was obscured by the induction of micro infarctions caused by the mode of administration. Therefore intracoronary application is not suitable for these cells. Although intracoronary injection is an easy and less invasive technique to administer cells post myocardial infarction, intramyocardial injection was shown to result in positive effects by Kim et al. In contrast to the cells used in the initial experimental rodent studies, bone marrow derived mononuclear cells are the most common used cells in clinical trials. In chapter six the capacity of mononuclear cells and unselected bone marrow in a pre-clinical porcine model of reperfused myocardial infarction is evaluated. Our model closely mimics the clinical setting of myocardial infarction with regards to the route of administration and timing of stem cell therapy given in clinical trials. Four weeks after treatment with mononuclear cell injection a decrease in infarct size is observed as measured with magnetic resonance imaging. This was not observed after injection of unselected bone marrow. Histology showed that there was a trend towards more calcifications in the infarct area after the injection of unselected bone marrow. However, there was no beneficial effect of mononuclear cell or unselected bone marrow therapy on left ventricular function after myocardial infarction. Our results after mononuclear cell injection do not differ from those of the clinical trial performed in Leuven, Belgium by Janssens et al. All clinical trials used the method of intermittent balloon occlusion during intracoronary injection of cells through the wire lumen of the balloon catheter, based on the assumption that this would yield increased adhesion of the injected cells to the vascular wall during the no-flow period, thereby leading to a higher cell engraftment. However, in our previous studies we used a selective probing injection catheter without interruption of blood flow. Therefore, we tested these different injection techniques in chapter seven. We observed no differences in the number of bone marrow mononuclear cells engrafted in the myocardium when applied through these two catheters (probing or balloon catheter). Therefore, the lack of effect on left ventricular function of bone marrow derived mononuclear cells in our study (which was described in chapter six), cannot be explained by the injection technique used. Since cultured umbilical cord blood cells can cause micro infarctions when administered intracoronary in healthy myocardium (chapter five), we investigated in chapter eight whether cultured bone marrow derived mononuclear cells could cause micro infarctions four days after injection in healthy myocardium. We found that this was the case for cultured cells, but not for freshly isolated cells. Cultured cells are larger in size compared to freshly isolated cells, which result in the obstruction of the microcirculation. Although clinical trials suggest that intracoronary stem cell injection is safe, cultured stem cells should be used with caution when applied intracoronary. The labeling of injected cells with iron to be able to track them in vivo with magnetic resonance imaging is assessed in chapter nine. This study showed that due to the hemoglobin breakdown products containing iron which is present in hemorrhagic areas in the reperfused infarct, iron labeling of intramyocardially injected cells is not suitable to track the stem cells after injection. Future directions Future studies are required to investigate whether hemorrhage induced signal voids cause similar interference with cell detection with magnetic resonance imaging after intracoronary injection in reperfused myocardial infarctions or after injection in non-reperfused infarcts. Gadolinium may be a more suitable marker than iron to track cells in vivo with magnetic resonance imaging in reperfused myocardial infarctions. It should be further investigated what the effect of injection of cultured cells is, when applying a different mode of administration, for example intramyocardial cell injection. The effect of the stem cells used in our model seems to be disappointing compared to earlier study results in small rodents. It is possible that in our model bone marrow derived mononuclear cells will have a positive effect on left ventricular function in time. Therefore, in new experiments, swine should be monitored for a longer follow-up time, e.g. 2, 3, 6 and 12 months. For these experiments miniature swine should be used. Differentiation of bone marrow derived stem cells in vitro towards cardiomyocytes is an option to enhance the effect of stem cell therapy in large mammals. However, it should always be tested whether these cultured cells induce microinfarctions when applied intracoronary. Pre-differentiation into cardiomoyocytes might prevent the differentiation of injected cells into fibroblasts or inflammatory cells. The pre-differentiation might replace scar tissue by viable cardiomyocytes, and this might enhance the effect on infarct size on left ventricular function in vivo after injection. However, if the new cardiomyocytes are not able to survive in ischemic tissue, it should be investigated whether additional cytokine injections are needed to induce angiogenesis in the infarct tissue to enhance cell survival. Patients benefit from optimal pharmacological treatment after myocardial infarction. Over time, ejection fraction will increase and infarct size will decrease in patients suffering from myocardial infarction due to remodeling which is influenced by optimal pharmacological treatment. Therefore, in a pre-clinical porcine model of myocardial infarction the combination of optimal pharmacological treatment and stem cell therapy could be tested to evaluate the additional effect of stem cell therapy on the recovery of function, infarct size and the remodeling after myocardial infarction. However first, in animal models, it is necessary to determine the optimal cell number required to obtain optimal effects of the cells on infarct size and left ventricular function. It should be investigated how to access the cells (e.g. bone marrow aspiration versus cytokine mobilization), and whether they should be expanded ex vivo. Second, it should be determined which cell type will have maximal clinical effects. Third, the optimal delivery method will have to be determined. Finally, understanding the mechanism of cardiac regeneration in animals will shed a light on the optimal therapy for patients. The potential effect of stem cell therapy in patients should finally be assessed in large, randomized, placebo-controlled, double-blind clinical trials