Fig. 2.

Several different methods of needle steering have been proposed in the literature: Asymmetry-based steering uses the forces generated at the tip during insertion to bend the needle. The tip curvature can be either constant or variable using multiple concentric cannulas. Base manipulation bends the needle by applying a force perpendicular to the insertion direction. Tissue manipulation can move the targets and obstacles into and out of the needle’s path, respectively. Each of these methods are conceptually independent, but may be combined, thereby increasing control authority over the needle trajectory.