Robotic-assisted real-time MRI-guided TAVR: from system deployment to in vivo experiment in swine model

Abstract

Purpose: Real-time magnetic resonance imaging (rtMRI) guidance provides significant advantages during transcatheter aortic valve replacement (TAVR) as it provides superior real-time visualization and accurate device delivery tracking. However, performing a TAVR within an MRI scanner remains difficult due to a constrained procedural environment. To address these concerns, a magnetic resonance (MR)-compatible robotic system to assist in TAVR deployments was developed. This study evaluates the technical design and interface considerations of an MR-compatible robotic-assisted TAVR system with the purpose of demonstrating that such a system can be developed and executed safely and precisely in a preclinical model.

Methods: An MR-compatible robotic surgical assistant system was built for TAVR deployment. This system integrates a 5-degrees of freedom (DoF) robotic arm with a 3-DoF robotic valve delivery module. A user interface system was designed for procedural planning and real-time intraoperative manipulation of the robot. The robotic device was constructed of plastic materials, pneumatic actuators, and fiber-optical encoders.

Results: The mechanical profile and MR compatibility of the robotic system were evaluated. The system-level error based on a phantom model was 1.14 ± 0.33 mm. A self-expanding prosthesis was successfully deployed in eight Yorkshire swine under rtMRI guidance. Post-deployment imaging and necropsy confirmed placement of the stent within 3 mm of the aortic valve annulus.

Conclusions: These phantom and in vivo studies demonstrate the feasibility and advantages of robotic-assisted TAVR under rtMRI guidance. This robotic system increases the precision of valve deployments, diminishes environmental constraints, and improves the overall success of TAVR.

Keywords: Cardiac surgery; MRI; Magnetic resonance; Robotic assistance; TAVR; Valve replacement.

Fig. 1

a A 25-mm modified Medtronic Freestyle^® bioprosthetic valve was mounted on a 26-mm self-expanding stent, with the annulus mounted 2 mm above the distal edge of the stent. b Bioprosthesis delivery systems. 1 outer sheath, 2 inner stick, 3 14 Fr hemostatic valve, 4 spacer for adjusting a snare loop catheter

Fig. 2

CAD layout of the robotic system with patient inside an MRI bore. 3-DoF valve delivery module (VDM) (D6–D8) is mounted on a 5-DoF Innomotion arm (D1–D5). The Innomotion arm was used for course position of the delivery device (D1–D5) in the trocar and fine trajectory adjustment (D4–D5). The VDM was used to manipulate delivery device for valve implantation

Fig. 3

a Typical profile for a commanded velocity with an amplitude of 3.5 mm/s and the actual Cartesian velocity measured using robot encoders. The velocity error was defined as the difference between the two velocities at that instant and described the smoothness in the changing of velocity. b Evaluation of velocity error based on amplitudes of commanded velocity. Values displayed demonstrate that the system tolerated a maximum user input speed of 3.6 mm/s and 3.6 °/s in order to keep the error below 0.5 mm/s and 0.5 °/s

Fig. 4

Prototype of the robotic valve deliverymodule (VDM). Front view (left) and back view (right). Delivery device was eliminated for improved viewing. The robotic module comprised of two linear joints: the translation joint (A) and insertion joint (B). (C) depicts the rotational joint

Fig. 5

Control interface showing connections between different subsystems and interactions of the operator with the system. The robotic assistant system for TAVR was comprised of three major subsystems: the imaging system, robotic system, and user interfaces. Initial MRI scan (S1, Siemens TrueFISP) during the preparatory phase was used to determine cardiac anatomy. Additional fine adjustments performed by the positioning module for the valve delivery device trajectory were performed during the intraoperative phase. The absence of preoperative registration was found to substantially improve efficiency without significant impact in accuracy

Fig. 6

Digital overlay markers were used to indicate critical anatomic landmarks, which were transposed in multiple imaging planes. a Long-axis view, b short-axis view. Blue markers indicate the takeoff positions of the left and right coronary ostia, while the yellow marker indicates the native aortic valve annulus

Fig. 7

Evaluation of positional error. Combination motion of translation and insertion joints to deploy self-expanding prosthesis. a The maximum position error was <0.5 mm and b its maximum position error rate was within 0.5 mm/s

Fig. 8

Phantom experimental setup. A phantom model was designed to emulate the dimensions of a valve replacement environment. A 25-mm-diameter plastic tube served as the aorta. A 12-mm trocar was inserted into a spherical joint. The distance from spherical joint to the end of the plastic tube was 50 mm, which is the average distance from the cardiac apex to the aorta annulus in the preclinical model

Fig. 9

Snapshots of rtMRI-guided robotic-assisted TAVR in a phantom model. a Orientation adjustment of the prosthesis. A passive marker was attached to the stent to visualize the orientation of the stent. The first image reveals that it is aligned with one coronary ostium, while the last image demonstrates it being aligned between the two coronary ostia. b Position adjustment of the prosthesis. c Deployment of the selfexpanding prosthesis

Fig. 10

Animal experimental setup. A prepared 55 kg Yorkshire swine was set on the MRI table with the delivery device inserted into the trocar.The robotic system displayed here was mounted

Fig. 11

Snapshot progression of rtMRI-guided robotic-assisted TAVR deployment sequence in the long-axis view (IFE navigation display omitted). a Initial position of delivery device. b Delivery device was aligned with desired trajectory. c Delivery device advanced across the aortic valve. d, e Sheath was retracted to deploy the valve. f Valve deployed