Towards dynamic real-time image guidance for cardiac catheter-based interventions
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Heart failure is a complex clinical syndrome, progressive in nature, and about half of patients who develop heart failure die within 5 years of diagnosis. This is a significant economic and healthcare burden that drives the need for novel and optimized cardiovascular treatment strategies. Current treatment strategies focus on prevention of further left ventricle (LV) deterioration and/or improvement of LV function, symptom relief, and prolongation of life. The complexity of cardiac interventions has increased due to technological development and the shift from complex surgical procedures to less invasive transcatheter-based procedures in combination with the rapid introduction of novel medical technology in clinical practice. A major focus to optimize the current cardiovascular treatment strategies has been hybrid imaging (HI). HI integrates multiple imaging modalities to provide visualization of the organs and soft tissues during the intervention. This thesis describes the development of a new 3D navigation technique based on HI for image-guided cardiac interventions. From bench to bedside we have developed the imaging technology, designed the testing methods, and performed the (pre-)clinical studies to assess its accuracy and clinical safety and feasibility. The development of the navigation technique required a novel, standardized, and reproducible whole-heart myocardial tissue processing method to perform validation of the targeting accuracy of intramyocardial injections. The protocol enables a detailed assessment of the cardiac anatomy and pathology and the intramyocardial injections in both 2D and 3D. Using the targeting accuracy validation protocol we demonstrated that the technology enables intramyocardial injections to be accurately guided towards predetermined target zones. Intramyocardial injection procedures were performed significantly faster compared to the clinical standard for intramyocardial injections. Since the technology uses the standard X-ray modality, procedures used significantly more fluoroscopy but was similar to an average percutaneous coronary intervention. Subsequently, the safety and feasibility of the technology was demonstrated in a first-in-man study, to provide per-procedural visualization of optimal pacing sites and image-guided LV lead placement during implantation of a cardiac resynchronization therapy device. We found similar CRT implant and fluoroscopy times compared to a historical cohort. Moreover, all LV leads were guided close to the target area, away from the myocardial scar and the course of the phrenic nerve. In addition, we have gained novel clinical insights from pre-clinical voltage mapping. We developed a novel method to predict the presence of scar, as defined by gold standard scar identification, by a statistical prediction model which uses multivariate mixed model logistic regression based on multiple electromechanical-parameters. We showed that our model has a strong predictive ability for the presence of myocardial scar. The comparison of feature tracking derived strain parameters to electromechanical-derived parameters of local mechanical activity revealed only weak correlations. All technologies were aimed at improving treatment planning, visualization, and guidance of complex cardiac interventions. The development steps described in this thesis accentuate how a medical technology specialist can be of importance for the clinical translation of medical technology. HI technology is an important technique in the growing need for optimization of complex cardiovascular interventions of heart failure patients.
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Catheter-driven cardiac interventions have emerged in response to the need of reducing invasiveness associated with the traditional cut-and-sew techniques. Catheter manipulation is traditionally performed under real-time fluoroscopy imaging, resulting in an overall trade-off of procedure invasiveness for radiation exposure of both the patient and clinical staff. Our approach to reducing and potentially eliminating the use of flouroscopy in the operating room entails the use of multi-modality imaging and magnetic tracking technologies, wrapped together into an augmented reality environment for enhanced intra-procedure visualization and guidance. Here we performed an in vitro study in which a catheter was guided to specific targets located on the endocardial atrial surface of a beating heart phantom. "Therapy delivery" was modeled in the context of a blinded procedure, mimicking a beating heart, intracardiac intervention. The users navigated the tip of a magnetically tracked Freezor 5 CRYOCATH catheter to the specified targets. Procedure accuracy was determined as the distance between the tracked catheter tip and the tracked surgical target at the time of contact, and it was assessed under three different guidance modalities: endoscopic, augmented reality, and ultrasound image guidance. The overall RMS targeting accuracy achieved under augmented reality guidance averaged to 1.1 mm. This guidance modality shows significant improvements in both procedure accuracy and duration over ultrasound image guidance alone, while maintianing an overall targeting accuracy comparable to that achieved under endoscopic guidance.
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The European research network Augmented Reality in Surgery (ARIS*ER) developed a system that supports minimally invasive cardiac surgery based on augmented reality (AR) technology. The system supports the surgical team during aortic endoclamping where a balloon catheter has to be positioned and kept in place within the aorta. The presented system addresses the two biggest difficulties of the task: lack of visualization and difficulty in maneuvering the catheter. The system was developed using a user centered design methodology with medical doctors, engineers and human factor specialists equally involved in all the development steps. The system was implemented using the AR framework Studierstube developed at TU Graz and can be used to visualize in real-time the position of the balloon catheter inside the aorta. The spatial position of the catheter is measured by a magnetic tracking system and superimposed on a 3D model of the patient's thorax. The alignment is made with a rigid registration algorithm. Together with a user defined target, the spatial position data drives an actuator which adjusts the position of the catheter in the initial placement and corrects migrations during the surgery. Two user studies with a silicon phantom show promising results regarding usefulness of the system: the users perform the placement tasks faster and more accurately than with the current restricted visual support. Animal studies also provided a first indication that the system brings additional value in the real clinical setting. This work represents a major step towards safer and simpler minimally invasive cardiac surgery.
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Robot-assisted surgical procedures are perpetually evolving due to potential improvement in patient treatment and healthcare cost reduction. Integration of an imaging modality intraoperatively further strengthens these procedures by incorporating the information pertaining to the area of intervention. Such information needs to be effectively rendered to the operator as a human-in-the-loop requirement. In this work, we propose a guidance approach that uses real-time MRI to assist the operator in performing robot-assisted procedure in a beating heart. Specifically, this approach provides both real-time visualization and force-feedback based guidance for maneuvering an interventional tool safely inside the dynamic environment of a heart's left ventricle. Experimental evaluation of the functionality of this approach was tested on a simulated scenario of transapical aortic valve replacement and it demonstrated improvement in control and manipulation by providing effective and accurate assistance to the operator in real-time.
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Endovascular procedures require real time visual feedback on the location of inserted catheters. This is currently achieved using X-ray fluoroscopy, which causes exposure to radiation. This study describes an alternative method using a robotic ultrasound system for catheter tracking and navigation in endovascular interventions, focusing on endovascular aneurysm repair. This approach relies on the registration of pre-operative images to provide both a tracking trajectory and visual feedback of the real-time catheter position. The procedure was validated on healthy volunteers and on a phantom that included a realistic vessel structure, showing an average tracking error of the moving catheter tip of 1.78±1.02 mm.
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Effective and safe performance of cardiovascular interventions requires excellent catheter/guidewire manipulation skills. These skills are currently mainly gained through an apprenticeship on real patients, which may not be safe or cost-effective. Computer simulation offers an alternative for core skills training. However, replicating the physical behaviour of real instruments navigated through blood vessels is a challenging task. We have developed VCSim3—a virtual reality simulator for cardiovascular interventions. The simulator leverages an inextensible Cosserat rod to model virtual catheters and guidewires. Their mechanical properties were optimized with respect to their real counterparts scanned in a silicone phantom using X-ray CT imaging. The instruments are manipulated via a VSP haptic device. Supporting solutions such as fluoroscopic visualization, contrast flow propagation, cardiac motion, balloon inflation, and stent deployment, enable performing a complete angioplasty procedure. We present detailed results of simulation accuracy of the virtual instruments, along with their computational performance. In addition, the results of a preliminary face and content validation study conveyed on a group of 17 interventional radiologists are given. VR simulation of cardiovascular procedure can contribute to surgical training and improve the educational experience without putting patients at risk, raising ethical issues or requiring expensive animal or cadaver facilities. VCSim3 is still a prototype, yet the initial results indicate that it provides promising foundations for further development.
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