MR-Compatible Steerable Biopsy Needle with Shape Memory Alloy
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Solution Overview
Problem
Current biopsy needles face challenges in accuracy due to needle deflection during insertion, particularly in MR-guided procedures, where existing steerable needle technologies are not MR-compatible and lack effective control over needle trajectory, especially in dense tissues like the prostate.
Innovation Solution
A steerable biopsy needle design featuring a removable stylet assembly with Shape Memory Alloys (SMA) and optical fibers for thermal activation, allowing for controlled deflection and rotation, integrated within an MR-compatible cannula, enabling precise needle guidance and shape sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a rigid needle body assumption is used for control, then the control strategy is simple, but the accuracy of needle path prediction deteriorates due to needle deflection during insertion
Solution Approach 1:
The needle is designed with a compliant section that allows dynamic deflection during insertion. The needle transitions from a rigid body assumption to a flexible structure that can bend and adapt to tissue resistance, enabling more accurate trajectory control through active deflection management rather than passive rigid insertion
Solution Approach 2:
Shape sensing technology is integrated into the needle to provide real-time feedback on needle deflection and position. This feedback enables closed-loop control strategies that actively compensate for tissue interactions and maintain accurate needle path prediction despite the compliant needle structure
2Measurement precision
If active needle steering technologies are used (magnetized compliant section, piezoelectric material, tendon-driven), then needle trajectory control is improved, but MR compatibility deteriorates due to interaction with magnetic fields and RF fields
Solution Approach 1:
The patent replaces magnetic actuation mechanisms with a mechanically actuated compliant needle design. The needle uses a compliant section with embedded tendons or shape memory alloys that can be actuated mechanically or thermally, eliminating the need for magnetized materials that would interfere with MR imaging while maintaining active steering capability
Solution Approach 2:
The needle structure incorporates a compliant section that changes its mechanical parameters (stiffness, flexibility) during insertion. By adjusting the compliance characteristics and actuation forces, the needle can achieve precise trajectory control without requiring MR-incompatible magnetic materials, as the steering is achieved through mechanical deformation and tissue interaction
3Manufacturing precision
If a thin tip needle is used for precision, then the ability to reach small structures is improved, but susceptibility to buckling increases
Solution Approach 1:
The needle incorporates a compliant section with a flexible structure that can bend and adapt to tissue contours. This flexible design allows the thin needle tip to reach small structures while the compliant section's geometric design and material properties provide buckling resistance through controlled flexibility rather than rigid strength
Solution Approach 2:
The needle is constructed as a composite structure with different sections having different mechanical properties. The proximal section provides structural support and buckling resistance, while the distal compliant section enables precise navigation to small structures. This composite design allows the thin tip to maintain strength through the overall needle structure rather than relying solely on tip rigidity
4Power
If pneumatic or hydraulic actuation systems are integrated in a small diameter needle, then power/volume ratio is improved, but device complexity and patient risk increase
Solution Approach 1:
The patent extracts the actuation mechanism from complex pneumatic or hydraulic systems and implements a simplified mechanical or thermal actuation system within the needle. The compliant section is actuated by tendons or shape memory alloys that can be controlled through external manipulation or thermal activation, eliminating the need for integrated fluid power systems in the small diameter needle while maintaining effective steering capability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides precise control over needle trajectory, enhancing accuracy in reaching small tumors or biopsy sites while being compatible with MR imaging, reducing the risk of imaging artifacts and tissue damage.
Implementation Method 1
The outer stylet part further has a shape material alloy (SMA) which is anchored on opposite ends of the extent of strain relieved slots such that when the SMA is thermally activated, the needle deflects in a direction which reduces the gaps of the strain relieved slots
Implementation Method 2
when the SMA is thermally activated
Implementation Method 3
The inner stylet having longitudinal excitation fibers for coupling photonic energy to the SMA
Data Source
AI summary
A biopsy needle has a cylindrical shell outer cannula and a stylet consisting of an inner stylet and outer stylet, both of which are inserted into the cylindrical cannula. The outer stylet has a series of strain relieved slits which provide bending over a deflection region in one direction, and the outer stylet is formed from a material such as a shape memory alloy (SMA) having a superelastic phase. The deflection is generated by an SMA wire spanning a deflection extent and attached to the outer stylet on either side of the deflection extent. The inner stylet, when positioned inside the outer stylet, has one or more actuation fibers which couple optical energy into the SMA wire, causing a deflection of the outer stylet over the deflection extent, with the optical energy provided to the actuation fibers for control of the deflection. Additional fibers may be placed in the inner stylet to measure temperature and to measure deflection.