Fluoroscopy-Free Tip Shape Estimation for Flexible Endoscope Using Permanent Magnet Positioning

Flexible endoscopes can reach the lesion via a small incision or the patient’s natural orifices, exhibiting minimally invasive or noninvasive diagnosis and surgery capabilities. Precise position and shape estimations of the soft tip are key to guarantee the precision of operation. Different from conventional fluoroscopy-based measurements, this article proposes a tip shape estimation method for flexible endoscopes based on permanent magnet positioning. A tip shape-sensing probe with embedded magnets is designed to be inserted into the working channel of the flexible endoscope, serving as positioning markers. Subsequently, the tip shape of the flexible endoscope is estimated using non-uniform rational B-spline (NURBS) curve approximation by optimizing the control points and weights via the path points, tangent lines, and tip length. Further, tip shape estimation experiments are conducted on a flexible ureteroscope and an upper gastrointestinal endoscope with the help of a G-arm surgical X-ray fluoroscopy system and computed tomography (CT) scanner, respectively. The mean contour error is measured to 0.6–1.3 mm for different bending angles. Experimental results demonstrate that the proposed method achieves a good estimation performance, thus showing great potential for fluoroscopy-free measurement and navigation in flexible endoscopic surgeries.