Tip design for safety of steerable needles for robot-controlled brain insertion

Abstract

Background Current practice in neurosurgical needle insertion is limited by the straight trajectories inherent with rigid probes. One technique allowing curvilinear trajectories involves flexible bevel-tipped needles, which bend during insertion due to their asymmetry. In the brain, safety will require avoidance of the sharp tips often used in laboratory studies, in favor of a more rounded profile. Steering performance, on the other hand, requires maximal asymmetry. Design of safe bevel-tipped brain needles thus involves management of this tradeoff by adjusting needle gauge, bevel angle, and fillet (or tip) radius to arrive at a design that is suitably asymmetrical while producing strain, strain rate, and stress below the levels that would damage brain tissue. Methods Designs with a variety of values of needle radius, bevel angle, and fillet radius were evaluated in finite-element simulations of simultaneous insertion and rotation. Brain tissue was modeled as a hyperelastic, linear viscoelastic material. Based on the literature available, safety thresholds of 0.19 strain, 10 s−1 strain rate, and 120 kPa stress were used. Safe values of needle radius, bevel angle, and fillet radius were selected, along with an appropriate velocity envelope for safe operation. The resulting needle was fabricated and compared with a Sedan side-cutting brain biopsy needle in a study in the porcine model in vivo (N=3). Results The prototype needle selected was 1.66 mm in diameter, with bevel angle of 10° and fillet radius of 0.25 mm. Upon examination of postoperative CT and histological images, no differences in tissue trauma or hemorrhage were noted between the prototype needle and the Sedan needle. Conclusions The study indicates a general design technique for safe bevel-tipped brain needles based on comparison with relevant damage thresholds for strain, strain rate, and stress. The full potential of the technique awaits the determination of more exact safety thresholds.

Three-dimensional nonlinear finite element model to estimate backflow during flow-controlled infusions into the brain

“…However, this 3D infusion model includes two particular layers of elements that consider indirectly the effect of the insertion in the tissue. Cannula insertion might be implemented through mesh-dependent damage theory and specific failure criterion of tissue, 80,81 but validation of this approach might be really challenging since that would require high computational resources and complex experimental information.…”

Gels, jets, mosquitoes, and magnets: a review of implantation strategies for soft neural probes

“…white matter versus grey matter versus vasculature), but also a time-dependent response to deformation [78,79]. These properties have been extensively investigated to create better models of injury-related deformations of brain tissue [80] for simulation and in silico optimization of surgical procedures, including the insertion of electrodes and needles into brain tissue [81].…”