A Magnetic Laser Scanner for Endoscopic Microsurgery

Laser scanners increase the quality of the laser microsurgery enabling fast tissue ablation with less thermal damage. Such technology is part of state-of-the-art freebeam surgical laser systems. However, laser scanning has not been incorporated to fiber-based lasers yet. This is a combination that has potential to greatly improve the quality of laser microsurgeries on difficult-to-reach surgical sites. Current fiberbased tissue ablations are performed in contact with the tissue, resulting in excessive thermal damage to healthy tissue in the vicinity of the ablated tissue. This is far from ideal for delicate microsurgeries, which require high-quality tissue incisions without any thermal damage or char formation. However, the possibility to perform scanning laser microsurgery in confined workspaces is restricted by the large size of currently available actuators, which are typically located outside the patient and require direct line-of-sight to the microsurgical area. Thus, it is desired to have the laser scanning feature in an endoscopic system to provide high incision quality in hard-to-reach surgical sites. This thesis aims to introduce a new endoscopic laser scanner to perform 2D position control and high-speed scanning of a fiber-based laser for operation in narrow workspaces. It also presents a technology concept aimed at assisting in incision depth control during soft-tissue microsurgery. The main objective of the work presented in this thesis is to bring the benefits of free-beam lasers to laser-based endoscopic surgery by designing an end-effector module to be placed at the distal tip of a flexible robot arm. To this end, the design and control of a magnetic laser scanner for endoscopic microsurgeries is presented. The system involves an optical fiber, electromagnetic coils, a permanent magnet and optical lenses in a compact system for laser beam deflection. The actuation mechanism is based on the interaction between the electromagnetic field and the permanent magnets. A cantilevered optical fiber is bended with the magnetic field induced by the electromagnetic coils by creating magnetic torque on the permanent magnet. The magnetic laser scanner provides 2D position control and high-speed scanning of the laser beam. The device includes laser focusing optics to allow non-contact incisions. A proof-of-concept device was manufactured and evaluated. It includes four electromagnetic coils and two plano-convex lenses, and has an external diameter of 13 mm. A 4 74 mm2 scanning range was achieved at a 30 mm distance from the scanner tip. Computer-controlled trajectory executions demonstrated repeatable results with 75 m precision for challenging trajectories. Frequency analysis demonstrated stable response up to 33 Hz for 3 dB limit. The system is able to ablate tissue substitutes with a 1940 nm wavelength surgical diode laser. Tablet-based control interface has been developed for intuitive teleoperation. The performance of the proof-of-concept device is analysed through control accuracy and usability studies. Teleoperation user trials consisting in trajectory-following tasks involved 12 subjects. Results demonstrated users could achieve an accuracy of 39 m with the magnetic laser scanner system. For minimally invasive surgeries, it is essential to perform accurate laser position control. Therefore, a model based feed-forward position control of magnetic laser scanner was developed for automated trajectory executions. First, the dynamical model of the system was identified using the electromagnets current (input) and the laser position (output). Then, the identified model was used to perform feedforward control. Validation experiments were performed with different trajectory types, frequencies and amplitudes. Results showed that desired trajectories can be executed in high-speed scanning mode with less than 90 m (1.4 mrad bending angle) accuracy for frequencies up to 15 Hz. State-of-the-art systems do not provide incision depth control, thus the quality of such control relies entirely on the experience and visual perception of the surgeons. In order to provide intuitive incision depth control in endoscopic microsurgeries, the concept of a technology was presented for the automated laser incisions given a desired depth based on a commercial laser scanner. The technology aims at automatically controlling laser incisions based on high-level commands from the surgeon, i.e. desired incision shape, length and depth. A feed-forward controller provides (i) commands to the robotic laser system and (ii) regulates the parameters of the laser source to achieve the desired results. The controller for the incision depth is extracted from experimental data. The required energy density and the number of passes are calculated to reach the targeted depth. Experimental results demonstrate that targeted depths can be achieved with \ub1100 m accuracy, which proves the feasibility of this approach. The proposed technology has the potential to facilitate the surgeon\u2019s control over laser incisions. The magnetic laser scanner enables high-speed laser positioning in narrow and difficult-to-reach workspaces, promising to bring the benefits of scanning laser microsurgery to flexible endoscopic procedures. In addition, the same technology can be potentially used for optical fiber based imaging, enabling for example the creation of new family of scanning endoscopic OCT or hyperspectral probes

Effects of geometric parameters on swimming of micro organisms with single helical flagellum in circular channels

We present a computational fluid dynamics (CFD) model for the swimming of micro organisms with a single helical flagellum in circular channels. The CFD model is developed to obtain numerical solutions of Stokes equations in three dimensions, validated with experiments reported in literature, and used to analyze the effects of geometric parameters, such as the helical radius, wavelength, radii of the channel and the tail and the tail length on forward and lateral swimming velocities, rotation rates, and the efficiency of the swimmer. Optimal shapes for the speed and the power efficiency are reported. Effects of Brownian motion and electrostatic interactions are excluded to emphasize the role of hydrodynamic forces on lateral velocities and rotations on the trajectory of swimmers. For thin flagella, as the channel radius decreases, forward velocity and the power efficiency of the swimmer decreases as well; however, for thick flagella, there is an optimal radius of the channel that maximizes the velocity and the efficiency depending on other geometric parameters. Lateral motion of the swimmer is suppressed as the channel is constricted below a critical radius, for which the magnitude of the lateral velocity reaches a maximum. Results contribute significantly to the understanding of the swimming of bacteria in micro channels and capillary tubes

Effects of poiseuille flows on swimming of magnetic helical robots in circular channels

This study reports experimental and numerical model results on swimming of microswimmers inside circular channels. Designed to mimic the swimming behavior of biological organisms at low Reynolds number flows, a number of microswimmers are manufactured utilizing a 3D printer and consist of a helical tail and a body that encapsulates a small magnet. The swimming motion results from the synchronized rotation of the artificial swimmer with the rotating magnetic field induced by three electromagnetic-coil pairs. In order to obtain linear and angular velocities and to analyze the motion of the microswimmer, a computational model is developed to obtain swimmer velocities from the solutions of three-dimensional steady Stokes equations which govern the flow around the swimmers inside the channel. Experiments and numerical simulations are carried out for a number of configurations with different geometric parameters and flow rates in the channel filled with glycerol. Numerical results agree well with experimentally measured average velocities of swimmers. Results describe the influence of the flow rate, length of the tail, diameter of the channel, and the direction of the rotation of the swimmer on the velocity and trajectories of microswimmers

Characterization and modeling of micro swimmers with helical tails and cylindrical heads inside circular channels

Micro swimming robots offer many advantages in biomedical applications, such as delivering potent drugs to specific locations in targeted tissues and organs with limited side effects, conducting surgical operations with minimal damage to healthy tissues, treatment of clogged arteries, and collecting biological samples for diagnostic purposes. Reliable navigation techniques for micro swimmers need to be developed to improve the localization of robots inside the human body in future biomedical applications. In order to estimate the dynamic trajectory of magnetically propelled micro swimmers in channels, that mimic blood vessels and other conduits, fluid-micro robot interaction and the effect of the channel wall must be understood well. In this study, swimming of one-link robots with helical tails is modeled with Stokes equations and solved numerically with the finite element method. Forces acting on the robot are set to zero to enforce the force-free swimming and obtain forward, lateral and angular velocities that satisfy the constraints. Effects of the number of helical waves, wave amplitude, relative size of the cylindrical head of micro swimmer and the radial position on angular and linear velocity vectors of micro swimmer are presented

\u3bcRALP and Beyond: Micro-Technologies and Systems for Robot-Assisted Endoscopic Laser Microsurgery

Laser microsurgery is the current gold standard surgical technique for the treatment of selected diseases in delicate organs such as the larynx. However, the operations require large surgical expertise and dexterity, and face significant limitations imposed by available technology, such as the requirement for direct line of sight to the surgical field, restricted access, and direct manual control of the surgical instruments. To change this status quo, the European project mu RALP pioneered research towards a complete redesign of current laser microsurgery systems, focusing on the development of robotic micro-technologies to enable endoscopic operations. This has fostered awareness and interest in this field, which presents a unique set of needs, requirements and constraints, leading to research and technological developments beyond mu RALP and its research consortium. This paper reviews the achievements and key contributions of such research, providing an overview of the current state of the art in robot-assisted endoscopic laser microsurgery. The primary target application considered is phonomicrosurgery, which is a representative use case involving highly challenging microsurgical techniques for the treatment of glottic diseases. The paper starts by presenting the motivations and rationale for endoscopic laser microsurgery, which leads to the introduction of robotics as an enabling technology for improved surgical field accessibility, visualization and management. Then, research goals, achievements, and current state of different technologies that can build-up to an effective robotic system for endoscopic laser microsurgery are presented. This includes research in micro-robotic laser steering, flexible robotic endoscopes, augmented imaging, assistive surgeon-robot interfaces, and cognitive surgical systems. Innovations in each of these areas are shown to provide sizable progress towards more precise, safer and higher quality endoscopic laser microsurgeries. Yet, major impact is really expected from the full integration of such individual contributions into a complete clinical surgical robotic system, as illustrated in the end of this paper with a description of preliminary cadaver trials conducted with the integrated mu RALP system. Overall, the contribution of this paper lays in outlining the current state of the art and open challenges in the area of robot-assisted endoscopic laser microsurgery, which has important clinical applications even beyond laryngology