Minimization of needle 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.