A Novel Flexible and Steerable Probe for Minimally Invasive Soft Tissue Intervention

Current trends in surgical intervention favour a minimally invasive (MI) approach, in which complex procedures are performed through increasingly small incisions. Specifically, in neurosurgery, there is a need for minimally invasive keyhole access, which conflicts with the lack of maneuverability of conventional rigid instruments. In an attempt to address this fundamental shortcoming, this thesis describes the concept design, implementation and experimental validation of a novel flexible and steerable probe, named “STING” (Soft Tissue Intervention and Neurosurgical Guide), which is able to steer along curvilinear trajectories within a compliant medium. The underlying mechanism of motion of the flexible probe, based on the reciprocal movement of interlocked probe segments, is biologically inspired and was designed around the unique features of the ovipositor of certain parasitic wasps. Such insects are able to lay eggs by penetrating different kinds of “host” (e.g. wood, larva) with a very thin and flexible multi-part channel, thanks to a micro-toothed surface topography, coupled with a reciprocating “push and pull” motion of each segment. This thesis starts by exploring these foundations, where the “microtexturing” of the surface of a rigid probe prototype is shown to facilitate probe insertion into soft tissue (porcine brain), while gaining tissue purchase when the probe is tensioned outwards. Based on these findings, forward motion into soft tissue via a reciprocating mechanism is then demonstrated through a focused set of experimental trials in gelatine and agar gel. A flexible probe prototype (10 mm diameter), composed of four interconnected segments, is then presented and shown to be able to steer in a brain-like material along multiple curvilinear trajectories on a plane. The geometry and certain key features of the probe are optimised through finite element models, and a suitable actuation strategy is proposed, where the approach vector of the tip is found to be a function of the offset between interlocked segments. This concept of a “programmable bevel”, which enables the steering angle to be chosen with virtually infinite resolution, represents a world-first in percutaneous soft tissue surgery. The thesis concludes with a description of the integration and validation of a fully functional prototype within a larger neurosurgical robotic suite (EU FP7 ROBOCAST), which is followed by a summary of the corresponding implications for future work

Energy shaping control for robotic needle insertion

This work investigates the use of energy shaping control to reduce deflection in slender beams with tip load and actuation at the base. The ultimate goal of this research is a buckling avoidance strategy for robotic-assisted needle insertion. To this end, the rigid-link model of a flexible beam actuated at the base and subject to tip load is proposed, and an energy shaping approach is employed to construct a nonlinear controller that accounts for external forces. A comparative simulation study highlights the benefits of the proposed approach over a linear control baseline and a simplified nonlinear control

Robotic System Development for Precision MRI-Guided Needle-Based Interventions

This dissertation describes the development of a methodology for implementing robotic systems for interventional procedures under intraoperative Magnetic Resonance Imaging (MRI) guidance. MRI is an ideal imaging modality for surgical guidance of diagnostic and therapeutic procedures, thanks to its ability to perform high resolution, real-time, and high soft tissue contrast imaging without ionizing radiation. However, the strong magnetic field and sensitivity to radio frequency signals, as well as tightly confined scanner bore render great challenges to developing robotic systems within MRI environment. Discussed are potential solutions to address engineering topics related to development of MRI-compatible electro-mechanical systems and modeling of steerable needle interventions. A robotic framework is developed based on a modular design approach, supporting varying MRI-guided interventional procedures, with stereotactic neurosurgery and prostate cancer therapy as two driving exemplary applications. A piezoelectrically actuated electro-mechanical system is designed to provide precise needle placement in the bore of the scanner under interactive MRI-guidance, while overcoming the challenges inherent to MRI-guided procedures. This work presents the development of the robotic system in the aspects of requirements definition, clinical work flow development, mechanism optimization, control system design and experimental evaluation. A steerable needle is beneficial for interventional procedures with its capability to produce curved path, avoiding anatomical obstacles or compensating for needle placement errors. Two kinds of steerable needles are discussed, i.e. asymmetric-tip needle and concentric-tube cannula. A novel Gaussian-based ContinUous Rotation and Variable-curvature (CURV) model is proposed to steer asymmetric-tip needle, which enables variable curvature of the needle trajectory with independent control of needle rotation and insertion. While concentric-tube cannula is suitable for clinical applications where a curved trajectory is needed without relying on tissue interaction force. This dissertation addresses fundamental challenges in developing and deploying MRI-compatible robotic systems, and enables the technologies for MRI-guided needle-based interventions. This study applied and evaluated these techniques to a system for prostate biopsy that is currently in clinical trials, developed a neurosurgery robot prototype for interstitial thermal therapy of brain cancer under MRI guidance, and demonstrated needle steering using both asymmetric tip and pre-bent concentric-tube cannula approaches on a testbed

Full 3D motion control for programmable bevel-tip steerable needles

Minimally invasive surgery has been in the focus of many researchers due to its reduced intra- and post-operative risks when compared to an equivalent open surgery approach. In the context of minimally invasive surgery, percutaneous intervention, and particularly, needle insertions, are of great importance in tumour-related therapy and diagnosis. However, needle and tissue deformation occurring during needle insertion often results in misplacement of the needles, which leads to complications, such as unsuccessful treatment and misdiagnosis. To this end, steerable needles have been proposed to compensate for placement errors by allowing curvilinear navigation. A particular type of steerable needle is the programmable bevel-tip steerable needle (PBN), which is a bio-inspired needle that consists of relatively soft and slender segments. Due to its flexibility and bevel-tip segments, it can navigate through 3D curvilinear paths. In PBNs, steering in a desired direction is performed by actuating particular PBN segments. Therefore, the pose of each segment is needed to ensure that the correct segment is actuated. To this end, in this thesis, proprioceptive sensing methods for PBNs were investigated. Two novel methods, an electromagnetic (EM)-based tip pose estimation method and a fibre Bragg grating (FBG)-based full shape sensing method, were presented and evaluated. The error in position was observed to be less than 1.08 mm and 5.76 mm, with the proposed EM-based tip tracking and FBG-based shape reconstruction methods, respectively. Moreover, autonomous path-following controllers for PBNs were also investigated. A closed-loop, 3D path-following controller, which was closed via feedback from FBG-inscribed multi-core fibres embedded within the needle, was presented. The nonlinear guidance law, which is a well-known approach for path-following control of aerial vehicles, and active disturbance rejection control (ADRC), which is known for its robustness within hard-to-model environments, were chosen as the control methods. Both linear and nonlinear ADRC were investigated, and the approaches were validated in both ex vivo brain and phantom tissue, with some of the experiments involving moving targets. The tracking error in position was observed to be less than 6.56 mm.Open Acces

Axially rigid steerable needle with compliant active tip control

Steerable instruments allow for precise access to deeply-seated targets while sparing sensitive tissues and avoiding anatomical structures. In this study we present a novel omnidirectional steerable instrument for prostate high-dose-rate (HDR) brachytherapy (BT). The instrument utilizes a needle with internal compliant mechanism, which enables distal tip steering through proximal instrument bending while retaining high axial and flexural rigidity. Finite element analysis evaluated the design and the prototype was validated in experiments involving tissue simulants and ex-vivo bovine tissue. Ultrasound (US) images were used to provide visualization and shape-reconstruction of the instrument during the insertions. In the experiments lateral tip steering up to 20 mm was found. Manually controlled active needle tip steering in inhomogeneous tissue simulants and ex-vivo tissue resulted in mean targeting errors of 1.4 mm and 2 mm in 3D position, respectively. The experiments show that steering response of the instrument is history-independent. The results indicate that the endpoint accuracy of the steerable instrument is similar to that of the conventional rigid HDR BT needle while adding the ability to steer along curved paths. Due to the design of the steerable needle sufficient axial and flexural rigidity is preserved to enable puncturing and path control within various heterogeneous tissues. The developed instrument has the potential to overcome problems currently unavoidable with conventional instruments, such as pubic arch interference in HDR BT, without major changes to the clinical workflow

Teleoperation of MRI-Compatible Robots with Hybrid Actuation and Haptic Feedback

Image guided surgery (IGS), which has been developing fast recently, benefits significantly from the superior accuracy of robots and magnetic resonance imaging (MRI) which is a great soft tissue imaging modality. Teleoperation is especially desired in the MRI because of the highly constrained space inside the closed-bore MRI and the lack of haptic feedback with the fully autonomous robotic systems. It also very well maintains the human in the loop that significantly enhances safety. This dissertation describes the development of teleoperation approaches and implementation on an example system for MRI with details of different key components. The dissertation firstly describes the general teleoperation architecture with modular software and hardware components. The MRI-compatible robot controller, driving technology as well as the robot navigation and control software are introduced. As a crucial step to determine the robot location inside the MRI, two methods of registration and tracking are discussed. The first method utilizes the existing Z shaped fiducial frame design but with a newly developed multi-image registration method which has higher accuracy with a smaller fiducial frame. The second method is a new fiducial design with a cylindrical shaped frame which is especially suitable for registration and tracking for needles. Alongside, a single-image based algorithm is developed to not only reach higher accuracy but also run faster. In addition, performance enhanced fiducial frame is also studied by integrating self-resonant coils. A surgical master-slave teleoperation system for the application of percutaneous interventional procedures under continuous MRI guidance is presented. The slave robot is a piezoelectric-actuated needle insertion robot with fiber optic force sensor integrated. The master robot is a pneumatic-driven haptic device which not only controls the position of the slave robot, but also renders the force associated with needle placement interventions to the surgeon. Both of master and slave robots mechanical design, kinematics, force sensing and feedback technologies are discussed. Force and position tracking results of the master-slave robot are demonstrated to validate the tracking performance of the integrated system. MRI compatibility is evaluated extensively. Teleoperated needle steering is also demonstrated under live MR imaging. A control system of a clinical grade MRI-compatible parallel 4-DOF surgical manipulator for minimally invasive in-bore prostate percutaneous interventions through the patient’s perineum is discussed in the end. The proposed manipulator takes advantage of four sliders actuated by piezoelectric motors and incremental rotary encoders, which are compatible with the MRI environment. Two generations of optical limit switches are designed to provide better safety features for real clinical use. The performance of both generations of the limit switch is tested. MRI guided accuracy and MRI-compatibility of whole robotic system is also evaluated. Two clinical prostate biopsy cases have been conducted with this assistive robot

Biomechanics of a parasitic wasp ovipositor : Probing for answers

Insects such as mosquitoes, true bugs, and parasitic wasps, probe for resources hidden in various substrates. The resources are often, located deep within the substrate and can only be reached with long and thin (slender) probes. Such probes can, however, easily bend or break (buckle) when pushed inside the substrate, which makes probing a challenging task. Nevertheless, the mentioned insects use their probes repeatedly throughout their lifetime without apparent damage. Furthermore, the probes are also used for sensing the targets, can be steered during insertion, and can transport both fluids (e.g. blood, phloem sap) and eggs. Insect probes seem highly versatile structures that satisfy many functional requirements, including buckling avoidance, steering, sensing, and transport. Similar requirements also hold for minimally invasive medical procedures, where slender tools are used to minimize damage to the patient. Understanding the probing process in insects can bring insights in the insect ecology and evolution and it may also help in the development of novel surgical tools. In this thesis, I focus on the mechanical and motor adaptations of insect probing, while other aspects are only briefly discussed. In chapter 2, we review the literature on the probing structures and their operating principles across mosquitoes, parasitic wasps, and hemipterans. Probes are either modified mouthparts (mosquitoes, true bugs) or special tubular outgrowths of the abdomen (parasitic wasps). Despite having different developmental origins, the probes share three major morphological characteristics, which may reflect the shared functional requirements of buckling avoidance and steering: (i) the probes consist of multiple, interconnected elements that can slide along each other, (ii) the probe diameters are very small, which leaves no space for internal musculature, and (iii) the distal ends (tips) of the probe elements are asymmetric and often bear various serrations, hooks, bulges, or notches. How such slender multi-element probes avoid buckling during insertion has been hypothesized in the so-called push–pull mechanism. According to this mechanism, the probe is inserted into the substrate by reciprocal movements of the elements. The insects therefore simultaneously push on some of the probe elements, while pulling on the others. The tip serrations are directed such, that they primarily increase the friction upon pulling of the elements. This puts the pulled elements under tension and makes them effectively stiffer in bending (like when pulling a rope). The elements under tension can serve as guides along which the other elements are pushed inside the substrate without the risk of buckling. The insect alternates the pushing and pulling between the elements to incrementally insert the probe in the substrate. This mechanism has, however, never been quantified in insects and it was hitherto unknown whether the animals rely on it during probing. The probe tip asymmetry presumably facilitates steering. The asymmetric tip geometry leads to asymmetric reaction forces from the substrate on the tip during insertion, which push the probe tip sideways into a curved path. Controlling the tip geometry therefore allows for control of probing direction. Although offsetting the elements by sliding already changes the shape of the probe tip, these changes might be too small to induce the necessary change of probing direction. A number of mechanisms that enhance the tip asymmetry during the sliding of the elements have been suggested. However, few mechanisms have been observed or studied in vivo, so it is not completely clear how insects steer with their probes. Additionally, the effect of the substrate on both the steering and insertion mechanisms is unknown. To understand the biomechanics of insect probing, we investigated the probing behaviour of the braconid parasitic wasp Diachasmimorpha longicaudata. This is an ideal species for studying the buckling avoidance and steering, because it: (i) possess a slender ovipositor several millimetres in length, (ii) probes into solid material (e.g. citrus fruits), and (iii) attack fruit-fly larvae that are freely moving within the substrate (i.e. steering can be expected). The ovipositor of D. longicaudata is similar to other hymenopterans and consists of three interconnected elements (valves), one dorsal and two ventral ones. The interconnection is a tongue-and-groove mechanism, which allows for sliding of the valves, but prevents their separation. The ovipositor has an asymmetric tip—the distal end of the dorsal valve is enlarged (bulge), while the ventral valve tips have harpoon-like serrations. Additionally, just proximal to the bulge of the dorsal valve, the ovipositor is characteristically bent in an S-shape. This seems to be a feature present only in D. longicaudata and closely related species. The wasps also possess a pair of sheaths that envelop the ovipositor at rest and throughout most of the probing process, but do not penetrate into the substrate. In chapter 3, we studied the kinematics of ovipositor insertion into translucent, artificial substrates of various stiffnesses. Ovipositor insertion was filmed in a three camera setup, which allowed us to reconstruct the ovipositor insertion in 3D, while also monitoring the orientation of the insect’s body. We discovered that the wasps can explore a wide range of the substrate by probing in any direction with respect to their body orientation from a single puncture point. Probing range and speed decreased with increasing substrate stiffness. Wasps used two strategies of ovipositor insertion. In soft substrates, all ovipositor valves were pushed inside the substrate at the same time. In stiff substrates, wasps always moved the valves alternatively, presumably employing the hypothesized push–pull mechanism. We observed that ovipositors can follow curved trajectories inside the substrate. Detailed kinematic analysis revealed that the ovipositors followed a curved path during probing with protracted ventral valve(s). In contrast, probing with protracted dorsal valve resulted in straight trajectories. We linked the changes in the probing direction to the shape changes in the ovipositor tip. When the ventral valves were protracted, they curved towards the dorsal valve, resulting in an enhanced bevel which presumably caused a change in insertion direction. In chapter 4, we investigated the above described steering mechanism by quantifying the bending stiffness (three point bend test) and the geometry (high-resolution computer tomography) of the ovipositor in D. longicaudata. Additionally, we qualitatively assessed the material composition of the valves using fluorescence imaging. The thick dorsal valve bulge might be stiff and could straighten the S-shaped region of the ovipositor during the valve offset, causing bending of the tip. We discovered that the S-shaped region of the ovipositor is significantly softer than its neighbouring regions, which is mostly due to the presence of resilin in the S-shaped region of the ventral valve. Resilin is a rubber-like protein and reduces the stiffness of the otherwise heavily sclerotized valves. Additionally, we showed that the ventral valves have a higher bending stiffness than the dorsal valve along most of their length. The exception is presumably the bulge on the dorsal valve—although we could not directly measure its bending stiffness, its geometrical properties show that it is the thickest (and therefore stiffest) region in the distal end of the ovipositor. Outside the substrate, offsetting of the valves in any direction (i.e. pro- or retraction of the ventral valves) caused a straightening of the S-shaped region of the ovipositor and a curving towards the dorsal side. However, during probing in a substrate, such curving was only observed upon protraction of the ventral valves. We hypothesize this is due to the interaction of the ovipositor with the substrate. Namely, the bevelled ventral valve tips generate substrate reaction forces that promote dorsal curving, while the bevelled tip of the dorsal valve generates substrate forces that promote ventral bending. The interaction between the ventral and dorsal valves straightens the S-shaped region of the ovipositor and enhances dorsal curving. This therefore facilitates strong shape changes of the tip only upon protraction of the ventral valves, while counteracting the ventral curving of the dorsal valve. These opposing mechanisms presumably result in an approximately straight protraction of the dorsal valve. In chapters 2 and 3 we describe how the wasps use the reciprocal valve movements when probing in stiff substrates. As such substrates presumably require strong forces during insertion, the reciprocal valve movements may indeed serve to avoid buckling. However, how the valves are actuated or the forces generated during probing have never been quantified. In chapter 5, we therefore investigated the ovipositor base and the muscles driving the movements of the valves. At the base, the valves attach to plate-like structures that are interconnected with a series of linkages. The muscles attach to these plates and can move them with respect to each other. Such movements also result in the movements of the valves. To analyse the mechanics of this linked system, we performed high-resolution computer tomography scans of wasps in different stages of the probing cycle. This allowed us to compare the configurational changes of the basal plates to the valve offset, and measure the muscle cross-sections and attachment sites. We also calculated the muscle moment arms and estimated the forces and moments of the most relevant musculature actuating the ovipositor movements, by assuming a tensile muscle stress previously reported for insect muscles. For the ventral valves only, we also calculated the forces the valves can exert onto the substrate. The dorsal valve can only be moved by moving the base that is linked inside the abdomen, and therefore force estimation could not be made. The displacement magnitude of the basal plates corresponded to the valve offset, indicating that the valves are indeed moved due to the changes in the arrangement of the basal plates. We also showed that the ventral valve plates move most during the probing cycle, while the magnitude of the dorsal valve plate movements is much smaller. This suggests that the ventral valves move along the dorsal valve, while the dorsal valve moves together with the abdomen during probing. Additionally, in the situation where the animal keeps its abdomen stationary, we estimated the maximal forces actuating the ventral valves. The estimated maximal pushing forces can be higher than the estimated buckling load of the unsupported ovipositor outside the substrate. Assuming the maximal pushing forces are required during probing, antibuckling mechanisms are needed to avoid damaging the ovipositor. Buckling can be limited (prevented) by either supporting the ovipositor outside the substrate with additional sheaths, employing the push–pull mechanism, or both. Subtracting the maximal estimated pushing and pulling forces on the ventral valves, results in a net pushing force that is very close to the buckling threshold of the ovipositor, albeit still slightly higher. The sheaths, although being flexible, might provide the additional support if needed. In this thesis, I show that multi-element probes are inserted into the substrate using reciprocal movements of the individual elements. These movements appear to be necessary in stiff substrates, which presumably require high pushing forces on a single element during probing. This is in accordance with the hypothesis that reciprocal valve movements serve as an anti-buckling mechanism. Additionally, such valve movements are also important for steering of the probe during insertion. The valve offset controls the shape of the probe tip and therefore the net substrate reaction forces that result in bending of the probe. Wasps evolved special structures that enhance the shape changes of their ovipositor tips and facilitate steering. Our findings may be interesting for a broad range of audiences. Entomologists, evolutionary biologists, and ecologists may find them useful when studying the diversification of probing insects, their evolutionary success, or their ecological interactions (e.g. insect–plant, parasite–host). The anti-buckling and steering mechanisms may be helpful when developing novel, man-made probes. These mechanisms allow for minimization of the probe thickness and accurate steering control, which minimizes substrate damage during probing. Our findings may be particularly useful in the development of slender, steerable needles for minimally invasive surgery.</p

Towards a procedure-optimised steerable catheter for deep-seated neurosurgery

In recent years, steerable needles have attracted significant interest in relation to minimally invasive surgery (MIS). Specifically, the flexible, programmable bevel-tip needle (PBN) concept was successfully demonstrated in vivo in an evaluation of the feasibility of convection-enhanced delivery (CED) for chemotherapeutics within the ovine model with a 2.5 mm PBN prototype. However, further size reductions are necessary for other diagnostic and therapeutic procedures and drug delivery operations involving deep-seated tissue structures. Since PBNs have a complex cross-section geometry, standard production methods, such as extrusion, fail, as the outer diameter is reduced further. This paper presents our first attempt to demonstrate a new manufacturing method for PBNs that employs thermal drawing technology. Experimental characterisation tests were performed for the 2.5 mm PBN and the new 1.3 mm thermally drawn (TD) PBN prototype described here. The results show that thermal drawing presents a significant advantage in miniaturising complex needle structures. However, the steering behaviour was affected due to the choice of material in this first attempt, a limitation which will be addressed in future work

Tendon-Driven Notched Needle for Robot-Assisted Prostate Interventions

M.S

SHAPE MEMORY ALLOY ACTUATOR CONTROL FOR 3D STEERING OF ACTIVE SURGICAL NEEDLE IN MINIMAL INVASIVE SURGERIES

Ph.D