Methods for Improving the Curvature of Steerable Needles in Biological Tissue

Abstract

Robotic needle steering systems have the potential to improve percutaneous interventions such as radiofrequency ablation of liver tumors, but steering techniques described to date have not achieved sufficiently small radius of curvature in biological tissue to be relevant to this application. In this work, the impact of tip geometry on steerable needle curvature is examined. Finite-element simulations and experiments with bent-tip needles in ex vivo liver tissue demonstrate that selection of tip length and angle can greatly improve curvature, with radius of curvature below 5 cm in liver tissue possible through judicious selection of these parameters. Motivated by the results of this analysis, a new articulated-tip steerable needle is described, in which a distal section is actively switched by a robotic system between a straight tip (resulting in a straight path) and a bent tip (resulting in a curved path). This approach allows the tip length and angle to be increased, while the straight configuration allows the needle tip to still pass through an introducer sheath and rotate inside the body. Validation testing in liver tissue shows that the new articulated-tip steerable needle achieves smaller radius of curvature compared to bent-tip needles described in previous work. Steerable needles with optimized tip parameters, which can generate tight curves in liver tissue, increase the clinical relevance of needle steering to percutaneous interventions.

Design and evaluation of a wasp-inspired steerable needle

“…2 The total length of the offset and stroke created between the wires can be seen as the length of a pre-bent segment. Adebar et al 3 showed that an increase in the length of the bent-tip leads to higher curvatures. In our case the values of this length (i.e., offset + stroke) are 8, 10, and 12 mm (see Table 2).…”

“…2 In cases in which the target is blocked by sensitive structures (e.g., vessels), much higher needle deflections are required (e.g., 30 mm) over a relatively short distance from the insertion point (e.g., 80 mm). 3 …”

The influence of tip shape on bending force during needle insertion

“…9. Based on previous work on shape-adaptable needles15161718, six different tip shapes were selected and compared. This is a subset of the tip types presented in the overview of van Gerwen et al 19…”

“…The influence of the choice of tissue simulant was assessed by performing experiments in both silicone-based and agar-agar-based materials. The conducted study is relevant for the formulation of explanatory, mechanics-based models, the optimization of tip designs, and the proper actuation of shape-adaptable needles, such as concentric tubes14, compliant needles15, and articulated-tip needles161718.…”

Endpoint Accuracy in Manual Control of a Steerable Needle

“…Tip-articulated needles do not require axial rotations for steering. They allow for both robotic (20,21) and manual approaches (6).…”