Fig. 1.

(a) The steering mechanism of asymmetric-tip needles [1] is due to forces between the tissue and needle tip that deflect the needle during insertion. Subsequent rotation of the needle shaft (from outside the patient) reorients the tip so that further insertion deflects the tip in a new direction. The combination of these two control inputs, along with a flexible needle shaft, allows the needle to reach targets not accessible by straight paths. (b) A steerable needle can reach subsurface targets not accessible using conventional needles and multiple targets can be reached without fully retracting the needle. Anatomical obstacles could include bones, vessels, nerves, and other structures that a needle might damage or not be able to penetrate.