Abstract
In this paper, a novel hybrid sensing method for tracking an ultrasonic endoscope within the gastrointestinal (GI) track is presented, and the prototype of the tracking system is also developed. We implement 6-DOF localization by sensing integration and information fusion. On the hardware level, a tri-axis gyroscope and accelerometer, and a magnetic angular rate and gravity (MARG) sensor array are attached at the end of endoscopes, and three symmetric cylindrical coils are placed around patients' abdomens. On the algorithm level, an adaptive fast quaternion convergence (AFQC) algorithm is introduced to determine the orientation by fusing inertial/magnetic measurements, in which the effects of magnetic disturbance and acceleration are estimated to gain an adaptive convergence output. A simplified electro-magnetic tracking (SEMT) algorithm for dimensional position is also implemented, which can easily integrate the AFQC's results and magnetic measurements. Subsequently, the average position error is under 0.3 cm by reasonable setting, and the average orientation error is 1° without noise. If magnetic disturbance or acceleration exists, the average orientation error can be controlled to less than 3.5°.
Highlights
Ultrasonic endoscopes are widely used in examining organs adjacent to the gastrointestinal (GI)track [1,2,3,4]
In the algorithm structure sections we have proven that the sampling cycle can affect the accuracy of both adaptive fast quaternion convergence (AFQC) and simplified electro-magnetic tracking (SEMT)
As can be seen from the table, the root-mean-square error (RMSE) in static state of the two algorithms are essentially equal on three Euler angles
Summary
Ultrasonic endoscopes are widely used in examining organs adjacent to the gastrointestinal (GI)track [1,2,3,4]. Electro-magnetic tracking (EMT) method has become a common practice in tracking endoscopes, including flexible [5,6,7]. In existing navigation systems for flexible endoscopes, magnetic generators are placed externally, while sensors are attached to the devices. Magnetic measurements are relatively stable; but when metal objects are near the system, distortions will appear and may significantly affect the measurement results. Ren [11] has reported that a small metal object can cause 10 degrees of distortions in a NDI (NDI, Waterloo, ON, Canada) EMT device. For a tracking system for ultrasonic endoscopes, the scan head is the major interference source, which will continuously disturb estimates [12]
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