Guidance in the hybrid cardiovascular procedure for ventricular septal defect closure

Abstract

Ventricular septal defects (VSDs) are holes between ventricular cavities that disturb the normal blood oxygenation process. VSDs are common congenital heart malformations that usually close by themselves; however, large VSDs require surgical treatment. A hybrid procedure aims to implant occluders to close VSDs during beating heart, being less invasive than the most common open heart surgery. The procedure is monitored with transesopageal echocardiography (TEE). TEE supplies images at high frame rates in real time; nevertheless, TEE provides a limited field of view that hinders maneuvering of surgical instruments inside the heart. Therefore, high experience is required to interpret the TEE images and to maneuver the surgical instruments. However, medical simulators for training in the hybrid procedure are limited; hence, practicing directly on patients could remain as the only alternative. The main goal of this thesis was to provide solutions to the problem of navigation guidance in the hybrid procedure to close VSDs. Those solutions are our three contributions that include: first, a method to design heart phantoms with VSDs for ultrasound imaging; second, a navigation guidance method to access VSDs for occluders implantation; and third, a cardiac motion tracking in ultrasound images of the heart with VSDs. Our first contribution tackled the problem of a lack of heart models for experimentation. To solve this problem, we developed a method to built heart phantoms with VSDs for palpation, puncture, and ultrasound image acquisition. We relied on diagnostic images from retrospective cases to accurately represent the cardiac anatomy of pediatric patients with VSDs. We made heart phantoms in two materials: silicone and polyvinyl alcohol cryogel (PVA-C); we found that PVA-C had the best echogenicity, which was important for VSD characterization in echocardiography. We believe that this contribution provides additional tools to master the exploration of VSDs for the hybrid procedure. Our second contribution tackled the problem of the limited field of view of TEE for guidance in the hybrid procedure. For the procedure’s guidance, we introduced a three-dimensional (3-D) virtual model of the patient’s heart and an electromagnetic measurement system (EMS) to track the surgical instruments. We validated a landmark registration method including heart phantoms, virtual heart models and the EMS in an experimental setup that we developed to simulate the hybrid procedure. A group of cardiologists performed the hybrid procedure on the heart phantoms, maneuvering the surgical instruments following the information provided by the virtual hearts. We found that the virtual heart models provided accurate information for guidance to access VSDs. We believe that this contribution is a successful proof of concept of a system that could provide guidance in a hybrid procedure, complementing TEE, to safely access VSDs. Up to this point, we provide guidance information in a static heart. In a real case, however, the heart beats. Therefore, our third contribution tackled the problem to track the heart motion in ultrasound images with the potential application to synchronize the guidance information (second contribution) with the cardiac cycle. We proposed a method based on particle filtering to predict the heart motion considering geometric parameters and intensity values of the ventricular cavities in TEE images. We found that the method was robust to blurry boundaries and missing information. We believe that automation of the heart tracking can potentially facilitate guidance in the hybrid procedure.

Date	21 Feb 2022
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Luc Duong (Supervisor), Sylvie Ratté (Co-supervisor) & Joaquim Miró (Co-supervisor)