A mitral annulus tracking approach for navigation of off-pump beating heart mitral valve repair

Novel Intracardiac Ultrasound Images Developed on a Cardiac Ultrasound Simulator and Validated in Live Horses

INTRODUCTION

Ultrasonographic guidance of catheter-based interventions in horses is based primarily on transthoracic echocardiography (TTE). Intracardiac echocardiography (ICE) has the potential to provide detailed imaging of specific cardiac regions. Insight and training in echocardiographic guidance can be acquired using an echocardiography simulator.

HYPOTHESIS/OBJECTIVES

Use an echocardiography simulator for horses to determine specific ICE views for catheter-based interventions and validate these in live horses.

ANIMALS

Six adult healthy experimental horses.

METHODS

Observational study. An echocardiographic phantom based on a three-dimensional computer model of the equine heart was used. This phantom was positioned in a water tank, allowing simultaneous TTE and ICE catheter introduction. Novel ICE images from within the thoracic inlet and right atrium were determined on the ultrasound simulator, with TTE as back-up modality to determine ICE catheter position in the simulator if necessary. Images were validated in six horses, with adaptations to catheter manipulations where needed.

RESULTS

Novel ICE images developed on the ultrasound simulator could be replicated in live horses, with no changes in catheter manipulations. These views allowed visualization of the tributaries of the cranial vena cava, both atria, pulmonary veins, aorta, and pulmonary artery.

CONCLUSIONS AND CLINICAL IMPORTANCE

The ultrasound simulator was useful in developing additional ICE images in order to understand echocardiographic anatomy. This simulator creates possibilities for ICE diagnosis of specific cardiac conditions and further development of ICE-guided catheter-based interventions in horses. The ultrasound simulator can be helpful for providing echocardiographic training and reduction of experimental animal use.

Navigation guidance for ventricular septal defect closure in heart phantoms

PURPOSE

Transesophageal echocardiography (TEE) is the preferred imaging modality in a hybrid procedure used to close ventricular septal defects (VSDs). However, the limited field of view of TEE hinders the maneuvering of surgical instruments inside the beating heart. This study evaluates the accuracy of a method that aims to support navigation guidance in the hybrid procedure.

METHODS

A cardiologist maneuvered a needle to puncture the patient's heart and to access a VSD, guided by information displayed in a virtual environment. The information displayed included a model of the patient's heart and a virtual needle that reproduced the position and orientation of the real needle in real time. The physical and the virtual worlds were calibrated with a landmark registration and an iterative closest point algorithms, using an electromagnetic measurement system (EMS). For experiments, we developed a setup that included heart phantoms representing the patient's heart.

RESULTS

Experimental results from two pediatric cases studied suggested that the information provided for guidance was accurate enough when the landmark registration algorithm was fed with coordinates of seven points clearly identified on the surfaces of the physical and virtual hearts. Indeed, with a registration error of 2.28 mm RMS, it was possible to successfully access two VSDs (6.2 mm and 6.3 mm in diameter) in all the attempts with a needle (5 attempts) and a guidewire (7 attempts).

CONCLUSION

We found that information provided in a virtual environment facilitates guidance in the hybrid procedure for VSD closure. A clear identification of anatomical details in the heart surfaces is key to the accuracy of the procedure.

3D localization of vena contracta using Doppler ICE imaging in tricuspid valve interventions

Purpose

Tricuspid valve (TV) interventions face the challenge of imaging the anatomy and tools because of the ‘TEE-unfriendly’ nature of the TV. In edge-to-edge TV repair, a core step is to position the clip perpendicular to the coaptation gap. In this study, we provide a semi-automated method to localize the VC from Doppler intracardiac echo (ICE) imaging in a tracked 3D space, thus providing a pre-mapped location of the coaptation gap to assist device positioning.

Methods

A magnetically tracked ICE probe with Doppler imaging capabilities is employed in this study for imaging three patient-specific TVs placed in a pulsatile heart phantom. For each of the valves, the ICE probe is positioned to image the maximum regurgitant flow for five cardiac cycles. An algorithm then extracts the regurgitation imaging and computes the exact location of the vena contracta on the image.

Results

Across the three pathological, patient-specific valves, the average distance error between the detected VC and the ground truth model is \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$({1.22 \pm 2.00})$$\end{document}(1.22±2.00)mm. For each of the valves, one case represented the outlier where the algorithm misidentified the vena contracta to be near the annulus. In such cases, it is recommended to retake the five-second imaging data.

Conclusion

This study presented a method for ultrasound-based localization of vena contracta in 3D space. Mapping such anatomical landmarks has the potential to assist with device positioning and to simplify tricuspid valve interventions by providing more contextual information to the interventionalists, thus enhancing their spatial awareness. Additionally, ICE can be used to provide live US and Doppler imaging of the complex TV anatomy throughout the procedure.

An Overview on Image Registration Techniques for Cardiac Diagnosis and Treatment

Image registration has been used for a wide variety of tasks within cardiovascular imaging. This study aims to provide an overview of the existing image registration methods to assist researchers and impart valuable resource for studying the existing methods or developing new methods and evaluation strategies for cardiac image registration. For the cardiac diagnosis and treatment strategy, image registration and fusion can provide complementary information to the physician by using the integrated image from these two modalities. This review also contains a description of various imaging techniques to provide an appreciation of the problems associated with implementing image registration, particularly for cardiac pathology intervention and treatments.

Patient-specific cardiac phantom for clinical training and preprocedure surgical planning

Minimally invasive mitral valve repair procedures including MitraClip^® are becoming increasingly common. For cases of complex or diseased anatomy, clinicians may benefit from using a patient-specific cardiac phantom for training, surgical planning, and the validation of devices or techniques. An imaging compatible cardiac phantom was developed to simulate a MitraClip^® procedure. The phantom contained a patient-specific cardiac model manufactured using tissue mimicking materials. To evaluate accuracy, the patient-specific model was imaged using computed tomography (CT), segmented, and the resulting point cloud dataset was compared using absolute distance to the original patient data. The result, when comparing the molded model point cloud to the original dataset, resulted in a maximum Euclidean distance error of 7.7 mm, an average error of 0.98 mm, and a standard deviation of 0.91 mm. The phantom was validated using a MitraClip^® device to ensure anatomical features and tools are identifiable under image guidance. Patient-specific cardiac phantoms may allow for surgical complications to be accounted for preoperative planning. The information gained by clinicians involved in planning and performing the procedure should lead to shorter procedural times and better outcomes for patients.