Identification of the Position of a Tethered Delivery Catheter to Retrieve an Untethered Magnetic Robot in a Vascular Environment

Abstract

In this paper, we propose a method of identifying the position of a tethered delivery catheter in a vascular environment, recombining an untethered magnetic robot (UMR) to the tethered delivery catheter, and safely retrieving them from the vascular environment in an endovascular intervention by utilizing a separable and recombinable magnetic robot (SRMR) and a magnetic navigation system (MNS). From images of a blood vessel and a tethered delivery catheter taken from two different angles, we developed a method of extracting the position of the delivery catheter in the blood vessel by introducing dimensionless cross-sectional coordinates. Then, we propose a retrieval method for the UMR by using the magnetic force considering the delivery catheter's position, suction force, and rotating magnetic field. We used thane MNS and feeding robot to simultaneously apply magnetic force and suction force to the UMR. In this process, we determined a current solution for generating magnetic force by using a linear optimization method. Finally, we conducted in vitro and in vivo experiments to verify the proposed method. In the in vitro experiment, which was in a glass tube environment, by using an RGB camera, we confirmed that the location of the delivery catheter in the glass tube could be recognized within an average error of 0.05 mm in each of the X- and Z-coordinates and that the retrieval success rate was greatly improved in comparison with that in the case without the use of magnetic force. In an in vivo experiment, we successfully retrieved the UMR in the femoral arteries of pigs.

Keywords: position identification; retrieval of an untethered magnetic robot; vascular environment.

Figure 1

(a) An SRMR composed of a tethered delivery catheter with a safety balloon and an untethered UMR; (b) structure of the connecting part of the delivery catheter; (c) structure of the UMR.

Figure 2

I-RAMAN system: (a) structure of the MNS; (b) the MNS with exterior housing; (c) structure of the feeding robot.

Figure 3

(a) Placement of the MNS and C-arm (X-ray imaging device) and the rotational axis of the C-arm; (b) definition of the oblique angle; (c) representation of pixel coordinates in an image.

Figure 4

(a) Representation of r_α1 in the cross-section of the blood vessel when the oblique angle is α₁; (b) representation of r_α2 in the cross-section of the blood vessel when the oblique angle is α₂; (c) DCSs with the vessel center ${\mathrm{P}}_{\mathrm{B}}^{\mathrm{D}\mathrm{C}\mathrm{S}}$, the center of the delivery catheter’s connecting part ${\mathrm{P}}_{\mathrm{C}}^{\mathrm{D}\mathrm{C}\mathrm{S}}$, and the UMR’s center ${\mathrm{P}}_{\mathrm{U}}^{\mathrm{D}\mathrm{C}\mathrm{S}}$.

Figure 5

(a) Magnetic forces applied to the UMR (F_g, F_r, and F_a); (b) magnetic force F_r applied to the radial direction of the blood vessel and the angle β between F_r and the X-axis of the blood vessel.

Figure 6

(a) F_r in the direction from the center of the blood vessel to the center of the delivery catheter in the cross-section of the blood vessel; (b) a UMR moving to the point where the direction of F_r makes a right angle with respect to the tangential vector of the inner wall of the blood vessel.

Figure 7

(a) Possible region of the center of the connecting part of the delivery catheter; (b) direction of F_r and β in region 1; (c) direction of F_r and β in region 2; (d) F_r in region 3.

Figure 8

Rotating magnetic field applied to the UMR.

Figure 9

Procedure for recombining the UMR with the delivery catheter by applying magnetic force F_m, a rotational magnetic field B_rot, and suction force to the UMR.

Figure 10

(a) Experimental setup for the in vitro experiment on the retrieval process; (b) 17 recombining positions; (c) oblique angle (α₁ = 0°, α₂ = −90°) and shooting direction of the RGB camera.

Figure 11

Actual and calculated positions on the cross-section of the glass tube (XZ-plane).

Figure 12

Images of the UMR and the delivery catheter in the jig aligned in the glass tube before and after applying magnetic force and suction force (camera direction: α₁ = 0°, α₂ = −90°).

Figure 13

(a) Success rate of recombination of the UMR with the delivery catheter without applying magnetic force; (b) with applying magnetic force.

Figure 14

X-ray images from the in vivo experiment: (a) separation; (b) forward motion; (c) backward motion; (d) retrieval.