Towards dynamic real-time image guidance for cardiac catheter-based interventions
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In the context of our ongoing objective to reduce morbidity associated with cardiac interventions, minimizing invasiveness has inevitably led to more limited visual access to the target tissues. To ameliorate these challenges, we provide the surgeons with a complex visualization environment that integrates interventional ultrasound imaging augmented with pre-operative anatomical models and virtual surgical instruments within a virtual reality environment. In this paper we present an in vitro study on a cardiac phantom aimed at assessing the feasibility and targeting accuracy of our surgical system in comparison to traditional ultrasound imaging for intra-operative surgical guidance. The "therapy delivery" was modeled in the context of a blinded procedure, mimicking a closed-chest intervention. Four users navigated a tracked pointer to a target, under guidance provide by either US imaging or virtual reality-enhanced ultrasound. A 2.8 mm RMS targeting error was achieved using our novel surgical system, which is adequate from both a clinical and engineering perspective, under the inherent procedure requirements and limitations of the system.
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In the past ten years, numerous new surgical and interventional techniques have been developed for treating heart valve disease without the need for cardiopulmonary bypass. Heart valve repair is now being performed in a blood-filled environment, reinforcing the need for accurate and intuitive imaging techniques. Previous work has demonstrated how augmenting ultrasound with virtual representations of specific anatomical landmarks can greatly simplify interventional navigation challenges and increase patient safety. These techniques often complicate interventions by requiring additional steps taken to manually define and initialize virtual models. Furthermore, overlaying virtual elements into real-time image data can also obstruct the view of salient image information. To address these limitations, a system was developed that uses real-time volumetric ultrasound alongside magnetically tracked tools presented in an augmented virtuality environment to provide a streamlined navigation guidance platform. In phantom studies simulating a beating-heart navigation task, procedure duration and tool path metrics have achieved comparable performance to previous work in augmented virtuality techniques, and considerable improvement over standard of care ultrasound guidance.
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Minimally invasive treatment of vascular disease demands dynamic navigation through complex blood vessel pathways and accurate placement of an interventional device, which has resulted in increased reliance on fluoroscopic guidance and commensurate radiation exposure to the patient and staff. Here we introduce a guidance system inspired by electric fish that incorporates measurements from a newly designed electrogenic sensory catheter with preoperative imaging to provide continuous feedback to guide vascular procedures without additional contrast injection, radiation, image registration, or external tracking. Electrodes near the catheter tip simultaneously create a weak electric field and measure the impedance, which changes with the internal geometry of the vessel as the catheter advances through the vasculature. The impedance time series is then mapped to a preoperative vessel model to determine the relative position of the catheter within the vessel tree. We present navigation in a synthetic vessel tree based on our mapping technique. Experiments in a porcine model demonstrated the sensor’s ability to detect cross-sectional area variation in vivo. These initial results demonstrate the capability and potential of this novel bioimpedance-based navigation technology as a non-fluoroscopic technique to augment existing imaging methods.
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In an effort to reduce morbidity during minimally- invasive cardiac procedures, we have recently developed an interventional technique targeted towards off-pump cardiac interventions. To compensate for the absence of direct visualization, our system employs a virtual reality environment for image guidance, that integrates pre-operative information with real-time intra-operative imaging and surgical tool tracking. This work focuses on enhancing intracardiac visualization and navigation by overlaying pre-operative cardiac models onto the intra-operative virtual space, to display surgical targets within their specific anatomical context. Our method for integrating pre-operative data into the intra-operative environment is accurate within ~5.0 mm. Thus, we feel that our virtually-augmented surgical space is accurate enough to improve spatial orientation and intracardiac navigation.
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Clinical research has been rapidly evolving towards the development of less invasive surgical procedures. We recently embarked on a project to improve intracardiac beating heart interventions. Our novel approach employs new surgical technologies and support from image-guidance via pre-operative and intra-operative imaging (i.e. two-dimensional echocardiography) to substitute for direct vision. Our goal was to develop a versatile system that allowed for safe cardiac port access, and provide sufficient image-guidance with the aid of a virtual reality environment to substitute for the absence of direct vision, while delivering quality therapy to the target. Specific targets included the repair and replacement of heart valves and the repair of septal defects. The ultimate objective was to duplicate the success rate of conventional open-heart surgery, but to do so via a small incision, and to evaluate the efficacy of the procedure as it is performed. This paper describes the software and hardware components, along with the methodology for performing mitral valve replacement as one example of this approach, using ultrasound and virtual tool models to position and fasten the valve in place.
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A major challenge in radiofrequency catheter ablation procedures is the voltage and activation mapping of the endocardium, given a limited mapping time. By learning from expert interventional electrophysiologists (operators), while also making use of an active-learning framework, guidance on performing cardiac voltage mapping can be provided to novice operators or even directly to catheter robots. A learning from demonstration (LfD) framework, based upon previous cardiac mapping procedures performed by an expert operator, in conjunction with Gaussian process (GP) model-based active learning, was developed to efficiently perform voltage mapping over right ventricles (RV). The GP model was used to output the next best mapping point, while getting updated towards the underlying voltage data pattern as more mapping points are taken. A regularized particle filter was used to keep track of the kernel hyperparameter used by GP. The travel cost of the catheter tip was incorporated to produce time-efficient mapping sequences. The proposed strategy was validated on a simulated 2D grid mapping task, with leave-one-out experiments on 25 retrospective datasets, in an RV phantom using the Stereotaxis Niobe® remote magnetic navigation system, and on a tele-operated catheter robot. In comparison with an existing geometry-based method, regression error was reduced and was minimized at a faster rate over retrospective procedure data. A new method of catheter mapping guidance has been proposed based on LfD and active learning. The proposed method provides real-time guidance for the procedure, as well as a live evaluation of mapping sufficiency.
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It is tedious and difficult to position a flexible catheter in a target vessel branch within complicated-shaped vessels owing to the lack of real-time visual feedback. Digital subtraction angiography and fluoroscopic guidance are currently used for catheter placement.The proposed method employs an electromagnetic (EM) tracking system to track a sensor-attached catheter. Vessel centerlines are extracted from the CT angiography image, based on which a navigational information tree is built to facilitate catheter manipulation. A virtual endoscopy technique is adopted to generate virtual intravascular video as visual feedback. Unscented Kalman filtering based image registration is performed to align the EM tracker frame with the anatomical atlas and to envision the target registration error.Preliminary experimental results showed the feasibility and effectiveness of the new method, with navigation accuracy of 1.80 ± 0.85 mm.The proposed method can provide continuous virtual visual feedback to facilitate catheter placement and has the potential for clinical use, with significant reduction in X-ray radiation exposure and doses of contrast agents.
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Percutaneous catheter-based techniques for the treatment of structural heart disease are becoming more complex, and current imaging techniques have limitations: while fluoroscopy gives poor visualisation of cardiac anatomical structures, echocardiography is limited in its ability to detect the position of catheters and devices. The EchoNavigator® (Philips) live image guidance tool is a novel system that integrates real-time echocardiography with fluoroscopic X-ray imaging, optimising the guidance and positioning of devices. Use of the EchoNavigator system facilitates improved understanding of anatomical structures while showing enhanced visualisation of catheter and device movements. Early clinical experience suggests that the technology is feasible and safe, and provides enhanced understanding of the relationship between soft tissue anatomy and catheter devices in structural heart disease. The use of the EchoNavigator system can improve the confidence of interventional cardiologists in the targeting and positioning of devices in percutaneous interventions in structural heart disease, and has the potential to reduce procedural time, reduce the dosage of contrast and radiation and increase safety in the performance of procedural steps.
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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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