Deflection of a flexible needle during insertion into soft tissue.

Accurate needle insertion into soft, inhomogeneous tissue is of practical interest because of its importance in percutaneous diagnosis and therapies. The needles used in such procedures are usually long flexible needles with bevel tips that can deflect during insertion. Deflection of the needle can not only cause misplacement of the needle tip at the target but can also cause the needle to deviate from the planned path due to the curvature created along the needle shaft. In order to reduce deflection of the needle from its path and to increase the accuracy of the needle tip placement, we have studied the relationship between the needle base forces/torques and the amount of needle deflection during needle insertion. The model proposed in this paper can be used to estimate the amount of needle deflection during insertion into relatively soft tissues. Such model may be integrated into a trajectory generation algorithm in order to increase needle tip placement accuracy.