Drape-Compatible Tool-Tip Localization for Hand-Held Laparoscopic Instruments via UWB Carrier-Phase Ranging and Trocar-Constrained Geometry

2026-09-30

AI Summary

This study addresses the challenge of instrument tip localization during laparoscopic surgery, where sterile drapes obstruct optical tracking paths. We propose a drape-agnostic positioning method that fuses ultra-wideband (UWB) carrier-phase ranging, inertial measurement unit (IMU) data, and trocar geometric constraints. The core innovation lies in exploiting the single-degree-of-freedom kinematic constraint of the trocar to directly resolve carrier-phase integer ambiguities, enabling high-precision estimation without dual-frequency hardware while remaining entirely unaffected by drape occlusion. Experimental results demonstrate that the proposed system achieves a positioning accuracy of 0.10–0.33 mm at update rates of 35–46 Hz within metallic instrument environments. Furthermore, its clinical feasibility has been successfully validated through in vivo appendectomy procedures on live rabbits.

Abstract

A surgical robot policy needs to know where each instrument's working end sits relative to the camera and to the other instrument, yet a laparoscopic operation leaves only the endoscope video, and a draped instrument hides every optical path on itself. We estimate the tool tips from distances and an IMU alone. The distances are measured by ultra-wideband carrier phase between antenna nodes on the handle side of the instruments: one per hand-held instrument, one on the endoscope, all outside the sterile barrier. Take the endoscope antenna as the reference. The two instrument antennas carry six coordinates while the three pairs give three distances, so the problem is short by three, and averaging cannot close that gap because what is missing is information, not precision. Carrier phase adds one more unknown per pair, an integer that leaves distance fixed only modulo lambda/2 = 23.1 mm. The trocar settles both difficulties: each shaft passes through a port whose position is known and whose direction the on-board IMU measures, so its antenna keeps a single degree of freedom, the insertion depth. Two unknowns now face three distances -- two fix the depths and the third is left over, and that spare equation exposes a wrong integer or a wrong mounting offset instead of absorbing it. The same solve returns both tool tips in the endoscope frame, without the second carrier frequency that integer resolution usually needs, so the link never leaves a single PLL lock. In an 11-hole phantom among metal instruments the three distances hold sigma = 0.10-0.33 mm at 35-46 Hz, a sterile drape pressed onto the antennas leaves the link unchanged where an optical path would be blocked, and the logger was carried into a live rabbit appendectomy.

Problem

• Tool-Tip Localization
• Laparoscopic Instruments
• Surgical Robotics
• Sterile Drape Occlusion

Innovation

• Ultra-Wideband Carrier-Phase Ranging
• Tool-Tip Localization
• Trocar-Constrained Geometry
• Integer Ambiguity Resolution
• Laparoscopic Instruments