Active Cannula Research Articles

Design and Validation of a Steerable Port Delivery Cannula System for Laser Interstitial Thermal Therapy

Abstract MRI (Magnetic Resonance Imaging) guided laser interstitial thermal therapy (LITT) is a procedure used for treating glioblastomas and epilepsy lesions in the brain. Current methods for placing LITT ablation probes use straight trajectories. This limits the treatment area, necessitating multiple passes of straight trajectories or risking untreated tumor margins. This work presents a port delivery cannula system (PDCS) to be integrated within existing surgical workflows of LITT, providing off-axis navigation to areas otherwise deemed inaccessible. The design of the PDCS is centered around a two-tube, Nitinol active cannula system, which delivers, places, and retracts a flexible, thermoplastic port along curved trajectories. We present the design of the PDCS system and validate it in free-space, phantom models, and ovine brain trials, with a specific focus on evaluating key parameters of port material characteristics. Eight commercial, biocompatible ports and five custom ports created using additive manufacturing were investigated. Results illustrate that ideal port characteristics include durometers between 85A-95A, a low coefficient of friction, and a wall thickness of approximately 20% of the overall port diameter. Our results also demonstrate that the PDCS system can achieve accuracies under 1mm in phantom models and 2mm in ovine tissue.

An Individually Controlled Multitined Expandable Electrode Using Active Cannula‐Based Shape Morphing for On‐Demand Conformal Radiofrequency Ablation Lesions

Being minimally invasive and highly effective, radiofrequency ablation (RFA) is widely used for small‐sized malignant tumor treatment. However, in clinical practice, a large number of tumors are found in irregular shape, while the current RFA devices are hard to control the morphologic appearance of RFA lesions on demand, which usually ends up with unnecessarily excessive tissue ablation and subsequently often brings irreversible damage to the organs’ functions. Herein, active cannulas for each of the individually controlled subelectrodes to achieve an on‐demand shape morphing and thus conformal RFA lesion are introduced. The target shape as well as the length of inserted subelectrodes can be precisely controlled by tuning the active stylets and cannulas. What's more, owing to independent movement and energy control of each subelectrodes, the electrode is shown to be not only efficient enough to accomplish accurate trajectory control to target tissue in a single insertion, but also adaptive enough to ablate target tissues with diverse morphologic appearances and locations. On‐demand conformal ablation of target tissue is demonstrated as well under the guidance of ultrasound imaging with the device. Potentially, the RFA electrode is a promising minimally invasive treatment of malignant tumors in future clinical practice. An interactive preprint version of the article can be found at: https://www.authorea.com/doi/full/10.22541/au.164019293.38729522.

Increasing the pulsatility of continuos flow VAD: comparison between a valvulated outflow cannula and speed modulation by simulation

To investigate by a lumped parameter model the feasibility of increasing the pulsatility of a continuous flow VAD,implanting an active valvulated outflow cannula and tocompare the resultswith the haemodynamic outcome given by speed modulation methods.The concomitant presence of speed modulation and the active valvulated outflow conduit is also simulated. A lumped parameter model was adopted. VAD was modeled starting from its pressure flow characteristics with a second order polynomial equation. The valvulated outflow conduit was modeled as an active resistance described by a square function. Starting from pathological condition we simulated: VAD; VAD and valvulated outflow conduit in copulsation, counterpulsation and asynchrony work with the heart; VAD and active valvulated outflow tube and speed modulation. Copulsation 1:1 andasynchrony 0.3s valve close-0.7s valve open configurationsmaximised the haemodynamic benefits with the highest increment in pulsatility. The valvulated outflow conduit causes a decrement of the left ventricular unloading and of VAD flow that can be counteracted by increasing the VAD speed without affecting pulsatility. The concomitant use of the speed modulation and the active valvulated outflow conduit can further increase the pulsatility without altering left ventricular unloading and VAD flow. The valvulated outflow tube provide similar increase in pulsatility to speed modulation method but causes a decrement of left ventricular unloading and VAD flow that can be counteracted increasing the VAD speed or allowing a partial support. A valvulated outflow tube can be potentially applied to all continuous flow VADs.

Comparisons of Lesion Volumes and Shapes Produced by a Radiofrequency System with a Cooled, a Protruding, or a Monopolar Probe

Background: Radiofrequency (RF) ablation for denervation has been utilized for decades in chronic pain management. This relies on the proper targeting of the affected nerve which may be obtained by creating an ablation lesion with a shape and volume that optimizes targeting. Various systems designed to improve lesion size are available. These include cooling the active tip (cooled-RF) and protruding the RF electrode outside the active tip (PERF). Objectives: This study compares lesion volumes of 3 commercially available RF systems: cooled-RF, “V” shaped active cannula and protruding electrode (18 g and 20 g), and monopolar RF (MRF; 16 g, 18 g, and 20 g). Study Design: Ex vivo study using clinically relevant conditions. Setting: Biophysical laboratory in an academic institution. Methods: RF ablation lesions were generated in additive-free chicken breast specimens (n = 10) with the RF probes fully inserted in them. For cooled RF, a 17 g probe (4 mm active tip) was used. RF was applied for 150 seconds at 60°C. PERF was applied using 18 g or 20 g introducers (10 mm active tip) for either 90 or 150 seconds at 80°C. For MRF ablation, introducers diameter were 16 g, 18 g, or 20 g (10 mm active tip), while RF was applied for 90 seconds at 80°C. Tissues were dissected through the midpoint of the lesion, and measurements of the longitudinal, transversal, and depth lengths were taken and used to calculate the lesion volume. Measurements from the distal edge in the transverse and longitudinal directions were also recorded. One-way ANOVA was used to determine statistical significance between volume means (P < 0.05). Results: Mean lesion volume with cooled RF (595 mm3 ) is significantly larger than any other mean volume measured. The second largest volume is produced with MRF using a 16 g introducer (360 mm3 ), which is significantly larger than those obtained with 18 g or 20 g. This is also significantly larger than the one obtained with PERF using an 18 g introducer. Mean lesion volume produced with PERF (80°C for 90 seconds) and an 18 g diameter tip (215 mm3 ) is significantly larger than the respective one produced with MRF (169 mm3 ). Increasing lesioning time to 150 seconds significantly increases the volume (283 mm3 ). Using a 20 g tip produces the smallest lesions at 80°C for 90 seconds with either PERF or MRF, although a lesioning time of 150 seconds makes it significantly larger (207 mm3 ). Limitations: The study is ex vivo and therefore does not account for the dynamic effects of the anatomy and physiology of a living organism. Conclusions: The results indicate that the lesion produced with a cooled-RF system (17 g, 4 mm tip) is significantly larger than that produced with either of the other systems trialed (18 g or 20 g, 10 mm active tip protruding electrode or 16 g, 18 g, or 20 g monopolar electrode). Interestingly, a 16 g, 10 mm active tip monopolar electrode produced a larger lesion than the one produced with the 18 g protruding electrode.

Design Choices in Needle Steering—A Review

Alignment errors can arise during needle tip placement in deep-seated tissue structures. This can lead to undesired diagnostic and therapeutic outcomes. Path correction by means of needle steering has been investigated in scientific studies for the past decades. Several approaches exist, each of them with their own strengths and weaknesses. This paper describes the various needle-steering techniques, and discusses their applicability in terms of mechanical design choices in order to assess and guide on-going work in this research area. Included steering techniques apply needle base manipulations, bevel tips, precurved stylets, active cannulas, programmable bevels, and tendon actuated tips. Techniques are classified as either passive or active, based on how steering is achieved. Mechanical properties of developed needles differ largely. Flexural rigidity, for instance, was found to vary with a factor 106. Mechanical interactions, such as torsion and buckling, are described individually. Different research objectives have led to different steerable needle designs. Design criteria are typically based on these objectives, and not necessarily on clinical needs. However, the effectiveness of steering techniques depends heavily on this design, the navigation medium, and the intended task. In the proposed classification scheme, this dependence is quantified by the flexural rigidity.

Feasibility of Shape Memory Alloy Wire Actuation for an Active Steerable Cannula

Needle insertion is used in many diagnostic and therapeutic percutaneous medical procedures such as brachytherapy, thermal ablations, and breast biopsy. Insufficient accuracy using conventional surgical cannulas motivated researchers to provide actuation forces to the cannula's body for compensating the possible errors of surgeons/physicians. In this study, we present the feasibility of using shape memory alloy (SMA) wires as actuators for an active steerable surgical cannula. A three-dimensional (3D) finite element (FE) model of the active steerable cannula was developed to demonstrate the feasibility of using SMA wires as actuators to bend the surgical cannula. The material characteristics of SMAs were simulated by defining multilinear elastic isothermal stress–strain curves that were generated through a matlab code based on the Brinson model. Rigorous experiments with SMA wires were done to determine the material properties as well as to show the capability of the code to predict a stabilized SMA transformation behavior with sufficient accuracy. In the FE simulation, birth and death method was used to achieve the prestrain condition on SMA wire prior to actuation. This numerical simulation was validated with cannula deflection experiments with developed prototypes of the active cannula. Several design parameters affecting the cannula's deflection such as the cannula's Young's modulus, the SMA's prestrain, and its offset from the neutral axis of the cannula were studied using the FE model. Real-time experiments with different prototypes showed that the quickest response and the maximum deflection were achieved by the cannula with two sections of actuation compared to a single section of actuation. The numerical and experimental studies showed that a highly maneuverable active cannulas can be achieved using the actuation of multiple SMA wires in series.

Parallel guidance endoscopic optical coherence tomography system for internal diagnosis through active cannulas

A parallel guidance endoscopic optical coherence tomography (OCT) system is proposed for minimally invasive internal inspection of inner organs or complex structures for diagnosis. The system is maneuvered to access the target using an active cannulas’ steerable structures. The integration of a specially designed linkage device with the developed system allows the OCT endoscope to scan with enhanced signal-collective performance, while maintaining its tip at a constant distance from the target, as well as expanding the scanning range. The proposed system is integrated with flexible active cannulas, and this prototype is used for testing. The test results show that the device reliably performs for biological samples. Thus, it could be implemented for various types of noninvasive diagnoses in situations involving small entrances or crooked passage to a target.

Design and Control of an Magnetic Resonance Compatible Precision Pneumatic Active Cannula Robot

The versatile uses and excellent soft tissue distinction afforded by magnetic resonance imaging (MRI) has led to the development of many MR-compatible devices for MRI-guided interventions. This paper presents a fully pneumatic MR-compatible robotic platform designed for neurosurgical interventions. Actuated by nonmagnetic pneumatic piston-cylinders, the robotic platform manipulates a five degree-of-freedom active cannula designed for deep brain interventions. Long lines of tubing connect the cylinders to remotely located pressure sensors and valves, and MRI-compatible optical sensors mounted on the robot provide the robot joint positions. A robust, nonlinear, model-based controller precisely translates and rotates the robot joints, with mean steady-state errors of 0.032 mm and 0.447 deg, respectively. MRI-compatibility testing in a 3-Tesla closed-bore scanner has shown that the robot has no impact on the signal-to-noise ratio, and that geometric distortion remains within recommended calibration limits for the scanner. These results demonstrate that pneumatic actuation is a promising solution for neurosurgical interventions that either require or can benefit from submillimeter precision. Additionally, this paper provides a detailed solution to the control problems imposed by severe nonlinearities in the pneumatic system, which has not previously been discussed in the context of MR-compatible devices.

Manual Active Cannula Deployment: Experimental Accuracy Evaluation in Free Space

Frontiers Abstracts Manual Active Cannula Deployment: Experimental Accuracy Evaluation in Free Space Marlena S. Clark, Marlena S. Clark Search for other works by this author on: This Site PubMed Google Scholar Jessica Burgner, Jessica Burgner Search for other works by this author on: This Site PubMed Google Scholar Philip J. Swaney, Philip J. Swaney Search for other works by this author on: This Site PubMed Google Scholar Robert J. Webster, III Robert J. Webster, III Department of Mechanical EngineeringVanderbilt University Search for other works by this author on: This Site PubMed Google Scholar Author and Article Information Robert J. Webster, III Department of Mechanical EngineeringVanderbilt University J. Med. Devices. Mar 2012, 6(1): 017592 (1 pages) https://doi.org/10.1115/1.4026770 Published Online: March 12, 2012 Article history Received: May 27, 2011 Revision Received: November 7, 2011

Design of an Autoclavable Active Cannula Deployment Device

Concentric tube continuum devices, known as active cannulas, consist of multiple pre-curved elastic tubes that extend telescopically and rotate axially with respect to each other. Through these degrees of freedom, an active cannula presents a dexterous and versatile “tentacle-like” mechanism for accessing targets in minimally invasive surgery. Deploying an active cannula in a practical surgical setting requires a sterilizable device capable of specifying positions and trajectories for each degree of freedom. While robotic devices will likely enable this to be done most efficiently in the future, initial clinical feasibility studies are best undertaken with manual devices. In this paper we present specifications, design and development of a manual (that is, not motorized) active cannula deployment device.

A Geometrically Exact Model for Externally Loaded Concentric-Tube Continuum Robots

Continuum robots, which are composed of multiple concentric, precurved elastic tubes, can provide dexterity at diameters equivalent to standard surgical needles. Recent mechanics-based models of these "active cannulas" are able to accurately describe the curve of the robot in free space, given the preformed tube curves and the linear and angular positions of the tube bases. However, in practical applications, where the active cannula must interact with its environment or apply controlled forces, a model that accounts for deformation under external loading is required. In this paper, we apply geometrically exact rod theory to produce a forward kinematic model that accurately describes large deflections due to a general collection of externally applied point and/or distributed wrench loads. This model accommodates arbitrarily many tubes, with each having a general preshaped curve. It also describes the independent torsional deformation of the individual tubes. Experimental results are provided for both point and distributed loads. Average tip error under load was 2.91 mm (1.5%-3% of total robot length), which is similar to the accuracy of existing free-space models.

Equilibrium Conformations of Concentric-tube Continuum Robots

Robots consisting of several concentric, preshaped, elastic tubes can work dexterously in narrow, constrained, and/or winding spaces, as are commonly found in minimally invasive surgery. Previous models of these “active cannulas” assume piecewise constant precurvature of component tubes and neglect torsion in curved sections of the device. In this paper we develop a new coordinate-free energy formulation that accounts for general preshaping of an arbitrary number of component tubes, and which explicitly includes both bending and torsion throughout the device. We show that previously reported models are special cases of our formulation, and then explore in detail the implications of torsional flexibility for the special case of two tubes. Experiments demonstrate that this framework is more descriptive of physical prototype behavior than previous models1 it reduces model prediction error by 82% over the calibrated bending-only model, and 17% over the calibrated transmissional torsion model in a set of experiments.

Parsimonious Evaluation of Concentric-Tube Continuum Robot Equilibrium Conformation

Dexterous at small diameters, continuum robots consisting of precurved concentric tubes are well-suited for minimally invasive surgery. These active cannulas are actuated by relative translations and rotations applied at the tube bases, which create bending via elastic tube interaction. An accurate kinematic model of cannula shape is required for applications in surgical and other settings. Previous models are limited to circular tube precurvatures, and neglect torsional deformation in curved sections. Recent generalizations account for arbitrary tube preshaping and bending and torsion throughout the cannula, providing differential equations that define cannula shape. In this paper, we show how to simplify these equations using Frenet-Serret frames. An advantage of this approach is the interpretation of torsional components of the preset tube shapes as "forcing functions" on the cannula's differential equations. We also elucidate a process for numerically solving the differential equations, and use it to produce simulations illustrating the implications of torsional deformation and helical tube shapes.

Aiming a Surgical Laser With an Active Cannula

An active cannula is a surgical device capable of dynamically changing its curved shape in response to rotation and translation of the several precurved, concentric, superelastic tubes from which it is made. As the tubes move with respect to one another in response to input motion at their bases (outside the patient), they elastically interact, causing one another to bend. This bending can be harnessed to direct the cannula through winding trajectories within the human body. An active cannula has the potential to perform a wide range of surgical tasks, and it is especially well suited for guiding and aiming an optical fiber (e.g. BeamPath from OmniGuide, Inc.) for laser ablation. Controlling the trajectory of the laser requires control of the shape of the active cannula, and in particular the position and orientation of its tip. Prior work has shown that beam mechanics can be used to describe the shape of the cannula, given the translations and axial angles of each tube base. Here, in order to aim the laser, we invert this relationship (obtaining the “inverse kinematic”), solving for the translations and axial angles of each tube, given a desired position and orientation of the cannula tip. Experimental evaluation of inverse kinematics was carried out using a prototype consisting of three tubes. The outermost tube is straight and rigid (stainless steel), with an outer diameter (OD) of 2.4 mm. The 1.8 mm OD middle tube is superelastic Nitinol, with a preshaped circular tip. The 1.4 mm OD innermost tube is Nitinol and is not precurved, representing the straight trajectory of a laser emanating from the tip of the cannula. We assessed the accuracy of the inverse kinematics by computing the necessary tube translations and rotations needed to direct the beam of the “laser” to sequential locations along a desired trajectory consisting of two line segments that meet at a corner. These inputs were then applied at tube bases to direct the laser to thirty points along the trajectory on a flat surface 100 mm away the cannula base. The position of the tip of the simulated laser was measured using an optical tracker (Micron Tracker H3-60, Claron, Inc.). Mean error between desired and actual positions was 3.1 mm (maximum 5.5 mm). This experiment demonstrates proof of concept for laser guidance, and establishes the accuracy of the inverse kinematic model. We note that these results are applicable to guidance of a wide range of medical devices in addition to lasers. Relevant references, as well as images of our prototype and experimental data described here can be found in an online version of this abstract at http://research.vuse.vanderbilt.edu/MEDLab/. This work was supported by NSF grant #0651803, and NIH grant #1R44CA134169-01A1.

Mechanics of Precurved-Tube Continuum Robots

This paper presents a new class of thin, dexterous continuum robots, which we call active cannulas due to their potential medical applications. An active cannula is composed of telescoping, concentric, precurved superelastic tubes that can be axially translated and rotated at the base relative to one another. Active cannulas derive bending not from tendon wires or other external mechanisms but from elastic tube interaction in the backbone itself, permitting high dexterity and small size, and dexterity improves with miniaturization. They are designed to traverse narrow and winding environments without relying on ldquoguidingrdquo environmental reaction forces. These features seem ideal for a variety of applications where a very thin robot with tentacle-like dexterity is needed. In this paper, we apply beam mechanics to obtain a kinematic model of active cannula shape and describe design tools that result from the modeling process. After deriving general equations, we apply them to a simple three-link active cannula. Experimental results illustrate the importance of including torsional effects and the ability of our model to predict energy bifurcation and active cannula shape.