Minimization of needte deflection in robot-assisted percutaneous therapy

Background Needle deflection and tissue deformation are two problems encountered during needle insertion into soft, non-homogeneous tissue. They affect the accuracy of needle placement, which in turn affects the effectiveness of needle-based therapies and biopsies. Methods in this study, a needle is inserted using a robot with two degrees of freedom. The needle is modelled as a flexible beam with clamped support at one end, and its deflection is estimated using online force/moment measurements at the needle base. To compensate for the needle deflection, the needle is axially rotated through 180 degrees. The needle deflection estimation data is used to find the insertion depths at which needle rotations are to be performed. Results A bevelled-tip needle was inserted into animal tissue. The needle deflection at the target was reduced by about 90%. It was observed that minimization of needle deflection reduced tissue deformation. The proposed method reduced needle deflection more than when needle insertion was performed with constant rotation. Conclusions Estimating needle tip position using online force/moment measurement improves the accuracy of robot-assisted percutaneous procedures when imaging feedback is not available. Copyright (C) 2007 John Wiley & Sons, Ltd.