A System to Track Stent Location in the Human Body by Fusing Magnetometer and Accelerometer Measurements

Abstract

This paper will introduce a simple locating system to track a stent when it is deployed into a human artery. The stent is proposed to achieve hemostasis for bleeding soldiers on the battlefield, where common surgical imaging equipment such as fluoroscopy systems are not available. In the application of interest, the stent must be guided to the right location to avoid serious complications. The most important features are its relative accuracy and the ease by which it may be quickly set up and used in a trauma situation. The locating approach in this paper utilizes a magnet outside the human body as the reference and a magnetometer that will be deployed inside the artery with the stent. The sensor can detect its location in a coordinate system centered with the reference magnet. In practice, the main challenge is that the locating accuracy will be deteriorated by external magnetic interference, rotation of the sensor, and random noise. These causes of error are addressed in the paper to improve the locating accuracy and repeatability under various conditions. Finally, the system's locating performance will be validated in benchtop experiments, where the effects of the disturbance-eliminating procedures will be addressed.

Keywords: location tracking; magnetic field; magnetometer; sensor fusion; stent guidance.

Figure 1

The structure of the impermeable stent and how it achieves hemostasis at the desired location in the aorta [3]. Reprinted/adapted with permission from Ref. [6], 2010, Wikimedia Commons.

Figure 2

The reference magnetic field and the detector trajectory in the torso. Reprinted/adapted with permission from Ref. [6], 2010, Wikimedia Commons.

Figure 3

The schematic and the fabricated detector with the sheath and stent.

Figure 4

Magnetic field components for a cylindrical magnet. (a) The radial $B_{\rho }$ and axial $B_z$ components in a vertical plane that pass through the cylinder center. (b) Decomposition of $B_{\rho }$ in a horizontal plane.

Figure 5

The magnetic field measurement of the permanent reference magnet and the disturbance.

Figure 6

Definition of roll($\phi$), pitch($\theta$), yaw($\psi$) angles. Reprinted/adapted with permission from Ref. [29], 2009, Wikimedia Commons.

Figure 7

(a) The schematic of the system. (b) The realization of the system in the lab.

Figure 8

Schematic of the system workflow, including the user interface that shows the sensor’s location relative to the origin.

Figure 9

Location measurements along three axes with the magnet height at 18 cm.

Figure 10

Validation of the disturbance-canceling method. (a) Extra magnets introduced as the disturbance sources. (b) The effect of the canceling algorithm.

Figure 11

The comparison of location measurements along three axes with and without the disturbance-canceling approach.

Figure 11

The comparison of location measurements along three axes with and without the disturbance-canceling approach.

Figure 12

The soft iron interference measurement test. (a) Disturbing objects added one after another around the magnetometer. (b) The slope values of the curves fitted to all datasets are close.

Figure 13

Using stepper motor as the rotation angle reference. (a) The sensor’s X axis is aligned with the motor shaft to change the roll angle. (b) The sensor’s Y axis is aligned with the motor shaft to change the pitch angle.

Figure 14

Experiment setup with all interfering factors.

Figure 15

Comparison between the measurement with and without all the disturbance correction procedures.

Figure 15

Comparison between the measurement with and without all the disturbance correction procedures.