An optical tracker based robot registration and servoing method for ultrasound guided percutaneous renal access

BACKGROUND Robot-assisted needle steering facilitates the percutaneous renal access (PRA) for their accuracy and consistency over manual operation. However, inaccurate image-robot correspondence and uncertainties in robot parameters make the needle track deviate from the intrarenal target. This paper aims to simplify the image-tracker-robot registration procedure and improves the accuracy of needle alignment for robot assisted ultrasound-guided PRA. METHODS First, a semi-automatic rigid registration is used for the alignment of the preoperative MR volume and the intraoperative orthogonal US slices. Passive markers are mounted both on US probe and robot end-effector, the planned puncture path is transferred from the MR volume frame into optical tracker frame. Tracker-robot correspondence and robot calibration are performed iteratively using a simplified scheme, both position and orientation information are incorporated to estimate the transformation matrix, only several key structural robot parameters and joint zero-positions are calibrated for simplicity in solving the inverse kinematic. Furthermore, an optical tracker feedback control is designed for compensating inaccuracies in robot parameters and tracker-robot correspondence, and improving the accuracy of needle alignment. The intervention procedure was implemented by a telemanipulated 5R1P robot, two experiments were conducted to validate the efficiency of robot-tracker registration method and the optical tracker feedback control, robot assisted needle insertion experiment was conducted on kidney phantom to evaluate the system performance. RESULTS The relative positioning accuracy of needle alignment is 0.24 ± 0.08 mm, the directional accuracy is 6.78 ± 1.65 × 10⁻⁴rad; the needle-target distance of needle insertion is 2.15 ± 0. 17 mm. The optical tracker feedback control method performs stable against wide range of angular disturbance over (0 ~ 0.4) radians, and the length disturbance over (0 ~ 100) mm. CONCLUSIONS The proposed optical tracker based robot registration and servoing method is capable of accurate three dimension needle operation for PRA procedure with improved precision and shortened time.