Fracture-Directed Steerable Needles

Abstract

Steerable needles hold the promise of improving the accuracy of both therapies and biopsies as they are able to steer to a target location around obstructions, correct for disturbances, and account for movement of internal organs. However, their ability to make late-insertion corrections has always been limited by the lower bound on the attainable radius of curvature. This paper presents a new class of steerable needle insertion where the objective is to first control the direction of tissue fracture with an inner stylet and later follow with the hollow needle. This method is shown to be able to achieve radius of curvature as low as 6.9[Formula: see text]mm across a range of tissue stiffnesses and the radius of curvature is controllable from the lower bound up to a near infinite radius of curvature based on the stylet/needle step size. The approach of “fracture-directed” steerable needles indicates the promise of the technique for providing a tissue-agnostic method of achieving high steerability that can account for variability in tissues during a typical procedure and achieve radii of curvature unattainable through current bevel-tipped techniques. A variety of inner stylet geometries are investigated using tissue phantoms with multiple stiffnesses and discrete-step kinematic models of motion are derived heuristically from the experiments. The key finding presented is that it is the geometry of the stylet and the tuning of the bending stiffnesses of both the stylet and the tube, relative to the stiffness of the tissue, that allow for such small radius of curvature even in very soft tissues.

Predictive mechanics-based model for depth of cut (DOC) of waterjet in soft tissue for waterjet-assisted medical applications

“…This research is done in line with developing motion models for a new class of steerable needles called Fracture-directed waterjet steerable needles [7], [66] and [8], in which the direction of tissue fracture is controlled by waterjet and then the flexible needle follows the path. Fig.…”

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

“…The above discussion of needle design innovations considers only bevel tip steerable needles, where insertion combined with axial shaft rotation is used to steer the needle. There are a number of other noteworthy steerable needle designs including (but not limited to) use of a curved stylet in conjunction with an outer cannula proposed in [19] and then later adapted with variations in stiffness and insertion approaches by others [20], [21], a programmable bevel which eliminates the need for axial rotation [22], and shape memory alloy actuation [23], among other innovative designs which are reviewed in [11]. Each of these prior steerable needle designs has its own unique strengths and weaknesses.…”

Resultant Radius of Curvature of Stylet-and-Tube Steerable Needles Based on the Mechanical Properties of the Soft Tissue, and the Needle

“…Different factors affect the radius of curvature of steerable needles while being inserted into the soft tissue. These factors include the mechanical properties of the soft tissue, tip geometry, and mechanical properties of the needle [1], [2], [3]. Several research groups have developed mechanics-based as well as non-physics based models to predict the insertion radius of traditional steerable needles based on the properties of the needle, and soft tissue [4], [5], [6].…”

“…1. Stylet-and-Tube Steerable Needles, in which the direction of the tissue fracture is controlled with the inner wire, and then the outer tube follows [1]. The combined radius of curvature is depend on step length, preset radius of the wire, tissue's mechanical properties, and tube & wire mechanical properties.…”

“…We have proposed a new class of steerable needles that we call fracture-directed stylet-and-tube steerable needles in which the direction of the tissue fracture is controlled by an inner stylet and then the flexible outer tube follows. This method has shown to achieve a radius of curvature as low as 6 mm in soft tissue phantoms which is unachievable by traditional steerable needles [1]. In order to fully characterize these steerable needles, we need to find a model that can predict the ROC of the steerable needle inside the soft tissue based on the mechanical properties of the needle, and the soft medium.…”