Observations of three-dimensional needle deflection during insertion into soft tissue

Accurate needle placement is important during percutaneous needle insertion procedures such as biopsy and brachytherapy. However, needle-tissue interactions may cause the needle to deviate from its intended path. In this paper, we have investigated the effects of insertion velocity, tip bevel angle and insertion profile on needle deflection in three-dimensional space (in-plane and out-of-plane). Experiments are done using soft-tissue simulant and chicken liver. The needle tip is tracked during insertion using stereoscopic cameras and an electromagnetic tracker. Experimental results show that the in-plane and out-of-plane deflection decreases, as insertion velocity increases. Varying the bevel angle from 30° to 60° is shown to decrease the in-plane deflection, and increase the out-of-plane deflection. The addition of rotational motion during continuous linear insertion decreases both the in-plane and out-of-plane deflection. Tapping during insertion does not produce significant reduction in the in-plane or out-of-plane deflection. An increase in the insertion velocity from 10 mm/s to 300 mm/s during insertion into chicken liver results in the decrease and increase in the in-plane and out-of-plane deflection, respectively. A monotonic increase in the out-of-plane deflection as insertion velocity increases is probably caused by the needle slipping while penetrating the outer capsule of the liver. The results of this study can be used to develop an accurate model of needle-tissue interactions.