Feedforward Coordinate Control of a Robotic Cell Injection Catheter

Abstract

Remote and robotically actuated catheters are the stepping-stones toward autonomous catheters, where complex intravascular procedures may be performed with minimal intervention from a physician. This article proposes a concept for the positional, feedforward control of a robotically actuated cell injection catheter used for the injection of myogenic or undifferentiated stem cells into the myocardial infarct boundary zones of the left ventricle. The prototype for the catheter system was built upon a needle-based catheter with a single degree of deflection, a 3-D printed handle combined with actuators, and the Arduino microcontroller platform. A bench setup was used to mimic a left ventricle catheter procedure starting from the femoral artery. Using Matlab and the open-source video modeling tool Tracker, the planar coordinates ( y, z) of the catheter position were analyzed, and a feedforward control system was developed based on empirical models. Using the Student's t test with a sample size of 26, it was determined that for both the y- and z-axes, the mean discrepancy between the calibrated and theoretical coordinate values had no significant difference compared to the hypothetical value of µ = 0. The root mean square error of the calibrated coordinates also showed an 88% improvement in the z-axis and 31% improvement in the y-axis compared to the unmodified trial run. This proof of concept investigation leads to the possibility of further developing a feedfoward control system in vivo using catheters with omnidirectional deflection. Feedforward positional control allows for more flexibility in the design of an automated catheter system where problems such as systemic time delay may be a hindrance in instances requiring an immediate reaction.

Keywords: catheterization; feedforward systems; intramyocardial injection; numerical models; robotic catheters.

Figure 1.

Model of the outer catheter guide (OCG) and inner operating catheter (IOC) with access to the left ventricle (LV) cavity. The OCG is preshaped to provide 2 stabilizing contact points in the aorta, and the IOC contains the necessary operating equipment to complete the procedure.

Figure 2.

(a) Rear view of the 3-dimensional model of catheter prototype handle. A mechanical slide actuates the inner handle, which is attached to the catheter body while up to 4 mechanical slides are attached to the walls of the inner handle, each capable of pulling 1 pull wire. (b) 3-dimensional (3-D) model of the holder and contraption for the syringe. (c) 3-D printed prototype of the catheter handle. (1) Nema 17 42 × 42 mm stepper motor. (2) 10 mm linear mechanical slide. (3) Stepper motor to pull wire connector. (4) Pull wire from catheter attached to connector. (5) Stepper motor slide is fixed onto the outer platform that slides the inner handle in a linear fashion. (6) Outer, nonmoving platform. (d) Arrangement of stepper motor and syringe fitted onto the 3-D printed components.

Figure 3.

Illustration of an Arduino Mega 2560 setup with stepper motors, TB6600 drivers, and an infrared receiver. Each stepper motor is fixed onto a mechanical slide that actuates the catheter pull wire, inner handle, or needle.

Figure 4.

(a) Bench setup of the robotic handle and catheter in an operational simulation. (b) Example of the catheter tip coordinates being tracked during linear movement and deflection. (c) Example of the needle protrusion length measured during tip deflection.

Figure 5.

A comparison between the theoretical and actual speeds of a loaded stepper motor.

Figure 6.

Behavioral profiles of the difference between the linear distance traveled by the catheter tip and the distance traveled by the actuator manipulating the catheter body. (a) Linear movement profile over different speeds. (b) Linear movement profile when changing directions at different lengths. (c) Linear movement profile when traveling in the same direction at different lengths.

Figure 7.

Stationary deflection profile where the tip coordinate is measured based on incremental actuation (ie, tension) of the pull wire.

Figure 8.

(a) Displacement in y-axis while the deflected catheter is being moved under compression. (b) Displacement in x-axis while the deflected catheter is being moved under tension.

Figure 9.

(a) Graph of the needle protrusion length compared to the needle actuator position after compression or forward movement. (b) Graph of the increase in protrusion length while the catheter is deflecting. (c) 3-dimensional (3-D) surface fit of the decrease in protrusion length while the needle actuator is retracting.

Figure 10.

Data sample of the calibrated catheter tip coordinates compared to theoretical and unmodified coordinate values.