Tracking and Characterization of Fragments in a Beating Heart Using 3D Ultrasound for Interventional Guidance

Abstract

Abstract. Fragments generated by explosions and similar incidents can become trapped in a patient's heart chambers, potentially causing disruption of cardiac function. The conventional approach to removing such foreign bodies is through open heart surgery, which comes with high perioperative risk and long recovery times. We thus advocate a minimally invasive surgical approach through the use of 3D transesophageal echocardiography (TEE) and a flexible robotic end effector. In a phantom study, we use 3D TEE to track a foreign body in a beating heart, and propose a modified normalized cross-correlation method for improved accuracy and robustness of the tracking, with mean RMS errors of 2.3 mm. Motion analysis of the foreign body trajectory indicates very high speeds and accelerations, which render unfeasible a robotic retrieval method based on following the tracked trajectory. Instead, a probability map of the locus of the foreign body shows that the fragment tends to occupy only a small sub-volume of the ventricle, suggesting a retrieval strategy based on moving the robot end effector to the position with the highest spatial probability in order to maximize the possibility of capture.

Guidance of a high dexterity robot under 3D ultrasound for minimally invasive retrieval of foreign bodies from a beating heart

“…This section reviews the findings of our previous efforts [8]- [10] in understanding foreign body behavior. Such knowledge is critical in moving forward with the design of a robotic system and capture strategies, so previous results are summarized here for context.…”

“…These factors motivate a relaxed retrieval approach wherein the end effector is aimed at a location where likelihood of intercept is greatest. We previously outlined the following criteria for computing these capture locations [8], [10].…”

“…In a precursor study [8], a 3.2-mm steel ball was inserted into the left ventricle of a beating heart phantom to mimic a clinical trauma case. The chosen stroke volume, about 18 ml, is lower than in healthy humans, reflecting surgical [28] and cardiovascular conditions following heart injury.…”

“…Under intraoperative 3D ultrasound guidance, the robot moves to secure the target, as illustrated in Fig. 1 In a previous study we tracked a foreign body in a beating heart phantom to characterize foreign body motion [8]. Then using an existing surgical robot, we demonstrated that the motion of the foreign body exceeds the ability of the robot to pursue it [9].…”

“…Then using an existing surgical robot, we demonstrated that the motion of the foreign body exceeds the ability of the robot to pursue it [9]. We thus introduced indirect capture strategies [8], [10] in which the moving target is ambushed rather than chased, thereby relaxing robot performance requirements.…”