Electromagnetically tracked guidewires for interventional procedures

Abstract

We developed and tested a small electromagnetically tracked 5DOF bone screw. We examined accuracy compared to conventional optical tracking systems and developed devices and techniques for implanting the sensor during an interventional percutaneous procedure. Finally we conducted “proof-of-concept” experiments for percutaneous spine procedures by implanting the tracking sensors in the vertebral body of an interventional phantom and cadaver. Experiments were done in an interventional fluoroscopy suite to evaluate the susceptibility of the magnetic tracking system to potential interference sources in a hospital setting. Despite the presence of environmental metal, we were able track it robustly throughout the volume of interest. By using two or more of these screws, a rigid body reference definition was created. In image space, fiducials embedded in the screws were easily visualized on fluoroscopic images. Orientation errors of the new screw compared to the RCM-PAKY robot averaged 0.8° compared to 0.2° for the bare coil. Positioning error compared to the robot averaged 1.7 mm for the screw and 1.9 mm for the bare coil. Largest discrepancies occurred at the extremes of the volume. When using six DOF targets (employing two coils), positioning error averaged 1.5 mm. The magnetically tracked bone screw has good potential for reducing the invasiveness of many procedures that currently require separate registration and tracking. Accuracy is acceptable in the operating room, and the technique is not a major departure from current clinical practice.