Decoupling Steerability From Diameter: Helical Dovetail Laser Patterning for Steerable Needles

Abstract

The maximum curvature of a steerable needle in soft tissue is highly sensitive to needle shaft stiffness, which has motivated use of small diameter needles in the past. However, desired needle payloads constrain minimum shaft diameters, and shearing along the needle shaft can occur at small diameters and high curvatures. We provide a new way to adjust needle shaft stiffness (thereby enhancing maximum curvature, i.e. "steerability") at diameters selected based on needle payload requirements. We propose helical dovetail laser patterning to increase needle steerability without reducing shaft diameter. Experiments in phantoms and ex vivo animal muscle, brain, liver, and inflated lung tissues demonstrate high steerability in soft tissues. These experiments use needle diameters suitable for various clinical scenarios, and which have been previously limited by steering challenges without helical dovetail patterning. We show that steerable needle targeting remains accurate with established controllers and demonstrate interventional payload delivery (brachytherapy seeds and radiofrequency ablation) through the needle. Helical dovetail patterning decouples steerability from diameter in needle design. It enables diameter to be selected based on clinical requirements rather than being carefully tuned to tissue properties. These results pave the way for new sensors and interventional tools to be integrated into high-curvature steerable needles.

A Recurrent Neural Network Approach to Roll Estimation for Needle Steering

“…Data Collection and Network Training: We implemented and evaluated our learning-based method on a robotic needle steering system previously presented in [12], designed to perform lung tumor biopsy through a bronchoscope. The steerable needle used was manufactured out of superelastic Nitinol measuring 1.24 mm OD, 1.0 mm ID, 1.3 m long (EuroFlex GmbH), fabricated using the method described in [13], and deployed through a clinical bronchoscope (Ambu USA). To collect the training data for our method, in the form of time series sequences of paired input and output vectors X and Y , we performed targeting insertions using a sliding mode controller [2] with a 6-DOF electromagnetic (EM) tracker embedded in the needle tip (Aurora NDI, Inc.).…”

Safer Motion Planning of Steerable Needles via a Shaft-to-Tissue Force Model

“…Due to their potential to reduce the invasiveness of many types of therapeutic and biopsy-based procedures, steerable needles have been proposed for use in the kidneys [11], liver [11], prostate [12], brain [13], and lung [14]. A large class of steerable needle designs leverage asymmetric tips, including bevelled [3], pre-bent [13], [15], passive flexure, [4], [16], variable-length flexure [17], active flexure [18], [19], and a programmable bevel [20]. See [5] for a review on steerable needle designs.…”

“…Bevel-tip steerable needles have the potential to provide minimally-invasive access to anatomical sites deep in the human body [1], [2], [3], [4]. These needles leverage asymmetric tip forces to curve around anatomical obstacles during needle insertion, enabling accurate targeting of clinicallyrelevant sites that are difficult or impossible to reach safely with traditional needles (see Fig.…”

“…However with an increase in curvature, more force is exerted upon the surrounding tissue during needle deployment. With large tissue forces perpendicular to the needle come an increased risk of a shearing event in which the needle shaft cuts sideways through the surrounding tissue, causing severe damage [4] (see Fig. 2).…”

“…The Cosserat string needle model is an idealization that becomes more accurate as the bending stiffness of the needle decreases. This is a particularly relevant assumption in light of recent advances in needle designs with decreased stiffness [4]. In addition, this approach admits an analytical solution for the tissue normal force that depends only on path geometry and frictional properties.…”