Waterjet fracture-directed steerable needles

Mahdieh Babaiasl; John Swensen

The focus of this proposal is on the new classes of steerable needles namely fracture-directed steerable needles, and two approaches to achieve this that are tube and stylet method, and water-jet method. 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. Stylet and tube fracture-directed steerable needles involve 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 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. Water-jet technology has been used extensively for decades industrially for many applications including mining, plastic, metal, stone, wood, and produce cutting. The use of water-jet in medical applications has been developed more recently and it is used for different applications such as soft tissue resection, bone cutting, wound debridement, and surgery. Water-jet fracture-directed steerable needles is a new application of water-jet technology in the medical field that harnesses the advantages of water-jet technology and steerable needle technology into one. A needle insertion system is designed and built, which has a custom-designed water-jet nozzle attached to a Nitinol needle as its ”needle”. Insertions with and without water-jet into 10%, 15% and 20% Poly (styrene-b-ethylene-co-butylene-b-styrene) triblock copolymer (SEBS) tissue-mimicking simulants are performed and the associated force data are measured using a force sensor at the base of the needle. Preliminary results of force vs. displacement showed that the water-jet reduces the insertion force associated with traditional needles by eliminating tip forces. For preliminary results, custom-designed straight nozzle is used to show the feasibility of water-jet steerable needles, whereas research underway is focused on steerability using steerable nozzles to improve steerability compared to current steerable needle technologies. Depth of cut as a function of fluid velocity is also measured for different volumetric flow rates. Preliminary results show that depth of cut is a linear function of fluid velocity when the width of the water-jet nozzle is sufficiently small and smooth. Research is underway to understand the characteristics of water-jet - tissue interaction, which is an important aspect to be explored to design better devices as well as path planning and control algorithms. To do so, a physics-based model to predict cutting depth, crack dimensions and insertion load on the needle based on parameters such as tissue properties (constitutive response and toughness), nozzle diameter, tip shape of the needle, and volumetric flow rate is the other aim of this proposal that is lacking in the literature. Another aim of the current proposal is using current path planning methods and proposing a control method for the developed water-jet steerable needle. In order to direct steerable needles to specific targets and avoid anatomical obstacles, planning paths through the patient’s anatomy is needed. Path planning of steerable needles is beyond the intuition of human beings because of complex kinematics, effects of tissue deformation, effects of tissue inhomogeneities, and other causes of motion uncertainty. Efficient computational methods for path planning enables using the full potential of steerable needles. Due to nonlinearity of needle steering, estimation and control problems are coupled. Controller-observed pairs are needed to estimate needle orientation. For image-guided control of water-jet needle steering, needle steering models should be used for model-based feedback controllers to steer the needle inside the tissue. Therefore the other aim of this proposal will be developing a controller to control water-jet needle to reach to a specified target.

Waterjet fracture-directed steerable needles

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