Publications by authors named "Robert J Webster"

73 Publications

Real-Time Localization of Cochlear-Implant Electrode Arrays Using Bipolar Impedance Sensing.

IEEE Trans Biomed Eng 2021 Aug 11;PP. Epub 2021 Aug 11.

Objective: Surgeons have no direct objective feedback on cochlear-implant electrode array (EA) positioning during insertion, yet optimal hearing outcomes are contingent on placing the EA as close as feasible to viable neural endings. This paper describes a system to non-invasively determine intracochlear positioning of an EA, without requiring any modifications to existing commercial EAs themselves.

Methods: Electrical impedance has been suggested as a way to measure EA proximity to the inner wall of the cochlea that houses auditory nerve endings the modiolus. In this paper, we extend prior work and demonstrate for the first time the relationship between bipolar access resistance and proximity of the EA to the modiolus (E-M proximity). We also evaluate two methods for producing direct, real-time estimates of E-M proximity from bipolar impedance measurements.

Results: We show that bipolar access resistance is highly correlated with E-M proximity and can be approximately modeled by a power law function. This one dimensional model is shown to be capable of producing accurate real-time estimates of E-M proximity, but its simplicity also limits the potential for future improvement. To address this challenge, we propose a new prediction approach based on a recurrent neural network, which generated an overall prediction accuracy of 93.7%.

Conclusion: Bipolar access resistance is highly correlated with E-M proximity, and can be used to estimate EA positioning.

Significance: This work shows how impedance sensing can be used to localize an EA during insertion into the small, enclosed cochlear environment, without requiring any modifications to existing clinically used EAs.
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http://dx.doi.org/10.1109/TBME.2021.3104104DOI Listing
August 2021

Closed-loop control of soft continuum manipulators under tip follower actuation.

Int J Rob Res 2021 Jun 15;40(6-7):923-938. Epub 2021 Mar 15.

Science and Technology of Robotics in Medicine (STORM) Laboratory UK, School of Electronic and Electrical Engineering, University of Leeds, Leeds, UK.

Continuum manipulators, inspired by nature, have drawn significant interest within the robotics community. They can facilitate motion within complex environments where traditional rigid robots may be ineffective, while maintaining a reasonable degree of precision. Soft continuum manipulators have emerged as a growing subfield of continuum robotics, with promise for applications requiring high compliance, including certain medical procedures. This has driven demand for new control schemes designed to precisely control these highly flexible manipulators, whose kinematics may be sensitive to external loads, such as gravity. This article presents one such approach, utilizing a rapidly computed kinematic model based on Cosserat rod theory, coupled with sensor feedback to facilitate closed-loop control, for a soft continuum manipulator under tip follower actuation and external loading. This approach is suited to soft manipulators undergoing quasi-static deployment, where actuators apply a follower wrench (i.e., one that is in a constant body frame direction regardless of robot configuration) anywhere along the continuum structure, as can be done in water-jet propulsion. In this article we apply the framework specifically to a tip actuated soft continuum manipulator. The proposed control scheme employs both actuator feedback and pose feedback. The actuator feedback is utilized to both regulate the follower load and to compensate for non-linearities of the actuation system that can introduce kinematic model error. Pose feedback is required to maintain accurate path following. Experimental results demonstrate successful path following with the closed-loop control scheme, with significant performance improvements gained through the use of sensor feedback when compared with the open-loop case.
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http://dx.doi.org/10.1177/0278364921997167DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8323997PMC
June 2021

Patient-specific, touch-based registration during robotic, image-guided partial nephrectomy.

World J Urol 2021 Jun 16. Epub 2021 Jun 16.

Department of Urology, Vanderbilt Institute for Surgery and Engineering (VISE), Vanderbilt University Medical Center, Nashville, TN, USA.

Image-guidance during partial nephrectomy enables navigation within the operative field alongside a 3-dimensional roadmap of renal anatomy generated from patient-specific imaging. Once a process is performed by the human mind, the technology will allow standardization of the task for the benefit of all patients undergoing robot-assisted partial nephrectomy. Any surgeon will be able to visualize the kidney and key subsurface landmarks in real-time within a 3-dimensional simulation, with the goals of improving operative efficiency, decreasing surgical complications, and improving oncologic outcomes. For similar purposes, image-guidance has already been adopted as a standard of care in other surgical fields; we are now at the brink of this in urology. This review summarizes touch-based approaches to image-guidance during partial nephrectomy, as the technology begins to enter in vivo human evaluation. The processes of segmentation, localization, registration, and re-registration are all described with seamless integration into the da Vinci surgical system; this will facilitate clinical adoption sooner.
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http://dx.doi.org/10.1007/s00345-021-03745-yDOI Listing
June 2021

Clinical Translation of an Insertion Tool for Minimally Invasive Cochlear Implant Surgery.

J Med Device 2021 Sep 2;15(3):031001. Epub 2021 Apr 2.

Department of Otolaryngology-Head and Neck Surgery, Vanderbilt University Medical Center, Nashville, TN 37232.

The objective of this paper is to describe the development of a minimally invasive cochlear implant surgery (MICIS) electrode array insertion tool concept to enable clinical translation. First, analysis of the geometric parameters of potential MICIS patients (N = 97) was performed to inform tool design, inform MICIS phantom model design, and provide further insight into MICIS candidacy. Design changes were made to the insertion tool based on clinical requirements and parameter analysis results. A MICIS phantom testing model was built to evaluate insertion force profiles in a clinically realistic manner, and the new tool design was evaluated in the model and in cadavers to test clinical viability. Finally, after regulatory approval, the tool was used for the first time in a clinical case. Results of this work included first, in the parameter analysis, approximately 20% of the population was not considered viable MICIS candidates. Additionally, one 3D printed tool could accommodate all viable candidates with polyimide sheath length adjustments accounting for interpatient variation. The insertion tool design was miniaturized out of clinical necessity and a disassembly method, necessary for removal around the cochlear implant, was developed and tested. Phantom model testing revealed that the force profile of the insertion tool was similar to that of traditional forceps insertion. Cadaver testing demonstrated that all clinical requirements (including complete disassembly) were achieved with the tool, and the new tool enabled 15% deeper insertions compared to the forceps approach. Finally, and most importantly, the tool helped achieve a full insertion in its first MICIS clinical case. In conclusion, the new insertion tool provides a clinically viable solution to one of the most difficult aspects of MICIS.
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http://dx.doi.org/10.1115/1.4050203DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8086187PMC
September 2021

Backward Planning for a Multi-Stage Steerable Needle Lung Robot.

IEEE Robot Autom Lett 2021 Apr 17;6(2):3987-3994. Epub 2021 Mar 17.

Department of Computer Science, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

Lung cancer is one of the deadliest types of cancer, and early diagnosis is crucial for successful treatment. Definitively diagnosing lung cancer typically requires biopsy, but current approaches either carry a high procedural risk for the patient or are incapable of reaching many sites of clinical interest in the lung. We present a new sampling-based planning method for a steerable needle lung robot that has the potential to accurately reach targets in most regions of the lung. The robot comprises three stages: a transorally deployed bronchoscope, a sharpened piercing tube (to pierce into the lung parenchyma from the airways), and a steerable needle able to navigate to the target. Planning for the sequential deployment of all three stages under health safety concerns is a challenging task, as each stage depends on the previous one. We introduce a new backward planning approach that starts at the target and advances backwards toward the airways with the goal of finding a piercing site reachable by the bronchoscope. This new strategy enables faster performance by iteratively building a single search tree during the entire computation period, whereas previous forward approaches have relied on repeating this expensive tree construction process many times. Additionally, our method further reduces runtime by employing biased sampling and sample rejection based on geometric constraints. We evaluate this approach using simulation-based studies in anatomical lung models. We demonstrate in comparison with existing techniques that the new approach (i) is more likely to find a path to a target, (ii) is more efficient by reaching targets more than 5 times faster on average, and (iii) arrives at lower-risk paths in shorter time.
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http://dx.doi.org/10.1109/lra.2021.3066962DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8087253PMC
April 2021

Magnetic Steering of Robotically Inserted Lateral-wall Cochlear-implant Electrode Arrays Reduces Forces on the Basilar Membrane In Vitro.

Otol Neurotol 2021 08;42(7):1022-1030

Department of Mechanical Engineering, University of Utah, Salt Lake City, Utah.

Hypothesis: Undesirable forces applied to the basilar membrane during surgical insertion of lateral-wall cochlear-implant electrode arrays (EAs) can be reduced via robotic insertion with magnetic steering of the EA tip.

Background: Robotic insertion of magnetically steered lateral-wall EAs has been shown to reduce insertion forces in vitro and in cadavers. No previous study of robot-assisted insertion has considered force on the basilar membrane.

Methods: Insertions were executed in an open-channel scala-tympani phantom. A force plate, representing the basilar membrane, covered the channel to measure forces in the direction of the basilar membrane. An electromagnetic source generated a magnetic field to steer investigational EAs with permanent magnets at their tips, while a robot performed the insertion.

Results: When magnetic steering was sufficient to pull the tip of the EA off of the lateral wall of the channel, it resulted in at least a 62% reduction of force on the phantom basilar membrane at insertion depths beyond 14.4 mm (p < 0.05), and these beneficial effects were maintained beyond approximately the same depth, even with 10 degrees of error in the estimation of the modiolar axis of the cochlea. When magnetic steering was not sufficient to pull the EA tip off of the lateral wall, a significant difference from the no-magnetic-steering case was not found.

Conclusions: This in vitro study suggests that magnetic steering of robotically inserted lateral-wall cochlear-implant EAs, given sufficient steering magnitude, can reduce forces on the basilar membrane in the first basilar turn compared with robotic insertion without magnetic steering.
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http://dx.doi.org/10.1097/MAO.0000000000003129DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8282696PMC
August 2021

Mechatronic Design of a Two-Arm Concentric Tube Robot System for Rigid Neuroendoscopy.

IEEE ASME Trans Mechatron 2020 Jun 27;25(3):1432-1443. Epub 2020 Feb 27.

Department of Mechanical Engineering at Vanderbilt University, Nashville, TN 37235, USA.

Open surgical approaches are still often employed in neurosurgery, despite the availability of neuroendoscopic approaches that reduce invasiveness. The challenge of maneuvering instruments at the tip of the endoscope makes neuroendoscopy demanding for the physician. The only way to aim tools passed through endoscope ports is to tilt the entire endoscope; but, tilting compresses brain tissue through which the endoscope passes and can damage it. Concentric tube robots can provide necessary dexterity without endoscope tilting, while passing through existing ports in the endoscope and carrying surgical tools in their inner lumen. In this paper we describe the mechatronic design of a new concentric tube robot that can deploy two concentric tube manipulators through a standard neuroendoscope. The robot uses a compact differential drive and features embedded motor control electronics and redundant position sensors for safety. In addition to the mechatronic design of this system, this paper contributes experimental validation in the context of colloid cyst removal, comparing our new robotic system to standard manual endoscopy in a brain phantom. The robotic approach essentially eliminated endoscope tilt during the procedure (17.09° for the manual approach vs. 1.16° for the robotic system). The robotic system also enables a single surgeon to perform the procedure - typically in a manual approach one surgeon aims the endoscope and another operates the tools delivered through its ports.
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http://dx.doi.org/10.1109/tmech.2020.2976897DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7971161PMC
June 2020

A Dynamic Model for Concentric Tube Robots.

IEEE Trans Robot 2020 Dec 27;36(6):1704-1718. Epub 2020 Jul 27.

Department of Mechanical, Aerospace, and Biomedical Engineering, The University of Tennessee, Knoxville, TN.

Existing static and kinematic models of concentric tube robots are based on the ordinary differential equations of a static Cosserat rod. In this paper, we provide the first dynamic model for concentric tube continuum robots by adapting the partial differential equations of a dynamic Cosserat rod to describe the coupled inertial dynamics of precurved concentric tubes. This generates an initial-boundary-value problem that can capture robot vibrations over time. We solve this model numerically at high time resolutions using implicit finite differences in time and arc length. This approach is capable of resolving the high-frequency torsional dynamics that occur during unstable "snapping" motions and provides a simulation tool that can track the true robot configuration through such transitions. Further, it can track slower oscillations associated with bending and torsion as a robot interacts with tissue at real-time speeds. Experimental verification of the model shows that this wide range of effects is captured efficiently and accurately.
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http://dx.doi.org/10.1109/TRO.2020.3000290DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7885994PMC
December 2020

Transurethral Anastomosis after Transurethral Radical Prostatectomy: A Phantom Study on Intraluminal Suturing With Concentric Tube Robots.

IEEE Trans Med Robot Bionics 2020 Nov 29;2(4):578-581. Epub 2020 Oct 29.

Department of Mechanical Engineering, Vanderbilt University.

Current surgical approaches to radical prostatectomy are associated with high rates of erectile dysfunction and incontinence. These complications occur secondary to the disruption of surrounding healthy tissue, which is required to expose the prostate. The urethra offers the least invasive access to the prostate, and feasibility has been demonstrated of enucleating the prostate with an endoscope using Holmium laser, which can itself be aimed by concentric tube robots. However, the transurethral approach to radical prostatectomy has thus far been limited by the lack of a suitable means to perform an anastomosis of the urethra to the bladder after prostate removal. Only a few intraluminal anastomotic devices currently exist, and none are small enough to pass through the urethra. In this paper we describe a new way to perform an anastomosis in the small luminal space of the urethra, harnessing the dexterity and customizability of concentric tube manipulators. We demonstrate a successful initial proof-of-concept anastomosis in an anthropomorphic phantom of the urethra and bladder.
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http://dx.doi.org/10.1109/tmrb.2020.3034735DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7694552PMC
November 2020

Accuracy of Touch-Based Registration During Robotic Image-Guided Partial Nephrectomy Before and After Tumor Resection in Validated Phantoms.

J Endourol 2021 03 11;35(3):362-368. Epub 2020 Nov 11.

Department of Urology, Vanderbilt University Medical Center, Nashville, Tennessee, USA.

Image-guided surgery (IGS) allows for accurate, real-time localization of subsurface critical structures during surgery. No prior IGS systems have described a feasible method of intraoperative reregistration after manipulation of the kidney during robotic partial nephrectomy (PN). We present a method for seamless reregistration during IGS and evaluate accuracy before and after tumor resection in two validated kidney phantoms. We performed robotic PN on two validated kidney phantoms-one with an endophytic tumor and one with an exophytic tumor-with our IGS system utilizing the da Vinci Xi robot. Intraoperatively, the kidney phantoms' surfaces were digitized with the da Vinci robotic manipulator via a touch-based method and registered to a three-dimensional segmented model created from cross-sectional CT imaging of the phantoms. Fiducial points were marked with a surgical marking pen and identified after the initial registration using the robotic manipulator. Segmented images were displayed via picture-in-picture in the surgeon console as tumor resection was performed. After resection, reregistration was performed by reidentifying the fiducial points. The accuracy of the initial registration and reregistration was compared. The root mean square (RMS) averages of target registration error (TRE) were 2.53 and 4.88 mm for the endophytic and exophytic phantoms, respectively. IGS enabled resection along preplanned contours. Specifically, the RMS averages of the normal TRE over the entire resection surface were 0.75 and 2.15 mm for the endophytic and exophytic phantoms, respectively. Both tumors were resected with grossly negative margins. Point-based reregistration enabled instantaneous reregistration with minimal impact on RMS TRE compared with the initial registration (from 1.34 to 1.70 mm preresection and from 1.60 to 2.10 mm postresection). We present a novel and accurate registration and reregistration framework for use during IGS for PN with the da Vinci Xi surgical system. The technology is easily integrated into the surgical workflow and does not require additional hardware.
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http://dx.doi.org/10.1089/end.2020.0363DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7987368PMC
March 2021

Comparing the accuracy of the da Vinci Xi and da Vinci Si for image guidance and automation.

Int J Med Robot 2020 Dec 1;16(6):1-10. Epub 2020 Sep 1.

Department of Mechanical Engineering, Vanderbilt University, Nashville, Tennessee, USA.

Background: Current laparoscopic surgical robots are teleoperated, which requires high fidelity differential motions but does not require absolute accuracy. Emerging applications, including image guidance and automation, require absolute accuracy. The absolute accuracy of the da Vinci Xi robot has not yet been characterized or compared to the Si system, which is now being phased out. This study compares the accuracy of the two.

Methods: We measure robot tip positions and encoder values assessing accuracy with and without robot calibration.

Results: The Si is accurate if the setup joints are not moved but loses accuracy otherwise. The Xi is always accurate.

Conclusion: The Xi can achieve submillimetric average error. Calibration improves accuracy, but excellent baseline accuracy of the Xi means that calibration may not be needed for some applications. Importantly, the external tracking systems needed to account for setup joint error in the Si are no longer required with the Xi.
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http://dx.doi.org/10.1002/rcs.2149DOI Listing
December 2020

A Novel Robotic Endoscopic Device Used for Operative Hysteroscopy.

J Minim Invasive Gynecol 2020 Nov - Dec;27(7):1631-1635. Epub 2020 Jun 12.

Division of Minimally Invasive Gynecology, Department of Obstetrics and Gynecology, Vanderbilt University Medical Center (Drs. Harvey, R. J. Webster, and Anderson).

To trial the use of a novel endoscopic robot that functions using concentric tube robots, enabling 2-handed surgery in small spaces, in a bioengineering laboratory. This was a feasibility study of the endoscopic robot for hysteroscopic applications, including removal of a simulated endometrial polyp. The endoscopic robot was successfully used to resect a simulated endometrial polyp from a porcine uterine tissue model in a fluid environment. The potential advantages of this platform to the surgeon may include improved exposure, finer dissection capability, and use of a 2-handed surgical technique. Further study regarding the safe, efficient, and cost-effective use of the endoscopic robot in gynecology is needed.
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http://dx.doi.org/10.1016/j.jmig.2020.06.009DOI Listing
February 2021

Eyes in Ears: A Miniature Steerable Digital Endoscope for Trans-Nasal Diagnosis of Middle Ear Disease.

Ann Biomed Eng 2021 Jan 26;49(1):219-232. Epub 2020 May 26.

Vanderbilt University Engineering Department, Nashville, TN, USA.

The aim of this work is to design, fabricate and experimentally validate a miniature steerable digital endoscope that can provide comprehensive, high-resolution imaging of the middle ear using a trans-nasal approach. The motivation for this work comes from the high incidence of middle ear diseases, and the current reliance on invasive surgery to diagnose and survey these diseases which typically consists of the eardrum being lifted surgically to directly visualize the middle ear using a trans-canal approach. To enable less-invasive diagnosis and surveillance of middle ear disease, we propose an endoscope that is small enough to pass into the middle ear through the Eustachian tube, with a steerable tip that carries a 1 Megapixel image sensor and fiber-optic illumination to provide high-resolution visualization of critical middle ear structures. The proposed endoscope would enable physicians to diagnose middle ear disease using a non-surgical trans-nasal approach instead, enabling such procedures to be performed in an office setting and greatly reducing invasiveness for the patient. In this work, the computational design of the steerable tip based on computed tomography models of real human middle ear anatomy is presented, and these results informed the fabrication of a clinical-scale steerable endoscope prototype. The prototype was used in a pilot study in three cadaveric temporal bone specimens, where high-quality middle ear visualization was achieved as determined by an unbiased cohort of otolaryngologists. This is the first paper to demonstrate cadaveric validation of a digital, steerable, clinical-scale endoscope for middle ear disease diagnosis, and the experimental results illustrate that the endoscope enables the visualization of critical middle ear structures (such as the epitympanum or sinus tympani) that were seldom or never visualized in prior published trans-Eustachian tube endoscopy feasibility studies.
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http://dx.doi.org/10.1007/s10439-020-02518-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7688494PMC
January 2021

Learning the Complete Shape of Concentric Tube Robots.

IEEE Trans Med Robot Bionics 2020 May 19;2(2):140-147. Epub 2020 Feb 19.

Department of Computer Science, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599 USA.

Concentric tube robots, composed of nested pre-curved tubes, have the potential to perform minimally invasive surgery at difficult-to-reach sites in the human body. In order to plan motions that safely perform surgeries in constrained spaces that require avoiding sensitive structures, the ability to accurately estimate the entire shape of the robot is needed. Many state-of-the-art physics-based shape models are unable to account for complex physical phenomena and subsequently are less accurate than is required for safe surgery. In this work, we present a learned model that can estimate the entire shape of a concentric tube robot. The learned model is based on a deep neural network that is trained using a mixture of simulated and physical data. We evaluate multiple network architectures and demonstrate the model's ability to compute the full shape of a concentric tube robot with high accuracy.
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http://dx.doi.org/10.1109/tmrb.2020.2974523DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7243456PMC
May 2020

Custom mastoid-fitting templates to improve cochlear implant electrode insertion trajectory.

Int J Comput Assist Radiol Surg 2020 Oct 14;15(10):1713-1718. Epub 2020 May 14.

Department of Otolaryngology, Vanderbilt University Medical Center, 1215 21st Avenue South, Suite 7209, Nashville, TN, 37232-8605, USA.

Purpose: Insertion trajectory affects final intracochlear cochlear implant (CI) positioning, but limited information is available intraoperatively regarding ideal trajectory. We sought to improve intracochlear positioning CI electrodes using custom templates to specify insertion trajectory.

Methods: 3D reconstructions were created from computed tomography of three cadaveric temporal bones. Trajectories co-planar with the straight segment of the cochlea's basal turn were considered ideal. Templates were designed to fit against the drilled mastoid's surface and convey this guided trajectory via a hollow cylinder. Templates were 3D-printed using stereolithography. Mastoidectomy was performed. Template accuracy was tested by measuring target registration error (TRE) for four templates. A novel, roller-based insertion tool (designed to fit within the template cylinder) constrained insertions to intended trajectories. Insertions were performed with MED-EL Standard electrodes in three bones with three conditions: guided trajectory with insertion tool, non-guided trajectory with insertion tool and guided trajectory with surgical forceps. For the final condition, the template was used to mark the mastoid to convey trajectory. Insertion was stopped when electrode buckling occurred.

Results: TRE ranged from 0.23 to 0.73 mm. Mean TRE ± standard deviation was 0.55 ± 0.19 mm. Insertions along guided versus non-guided trajectories averaged more intracochlear electrodes (9, 8, 8 vs. 7, 7, 8) and greater angular insertion depths (AID) (377°, 341°, 320° vs. 278°, 302°, 290°). Insertions performed with forceps using templates as a guide also achieved excellent results (intracochlear electrodes: 10, 7, 8; AID: 478°, 318°, 333°). No translocations occurred.

Conclusion: Custom mastoid-fitting templates reliably specify intended insertion trajectory and provide sufficient information for recreation of that trajectory with manual insertion after template removal. The templates can accurately target structures within the temporal bone with a TRE of 0.55 ± 0.19 mm. Our roller-based insertion tool achieves results comparable to manual insertion using surgical forceps.
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http://dx.doi.org/10.1007/s11548-020-02193-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8163487PMC
October 2020

Online Disturbance Estimation for Improving Kinematic Accuracy in Continuum Manipulators.

IEEE Robot Autom Lett 2020 Apr 10;5(2):2642-2649. Epub 2020 Feb 10.

Science and Technology of Robotics in Medicine (STORM) Laboratory UK, School of Electronic and Electrical Engineering, University of Leeds, Leeds, UK.

Continuum manipulators are flexible robots which undergo continuous deformation as they are actuated. To describe the elastic deformation of such robots, kinematic models have been developed and successfully applied to a large variety of designs and to various levels of constitutive stiffness. Independent of the design, kinematic models need to be calibrated to best describe the deformation of the manipulator. However, even after calibration, unmodeled effects such as friction, nonlinear elastic and/or spatially varying material properties as well as manufacturing imprecision reduce the accuracy of these models. In this paper, we present a method for improving the accuracy of kinematic models of continuum manipulators through the incorporation of orientation sensor feedback. We achieve this through the use of a "disturbance wrench", which is used to compensate for these unmodeled effects, and is continuously estimated based on orientation sensor feedback as the robot moves through its workspace. The presented method is applied to the HydroJet, a waterjet-actuated soft continuum manipulator, and shows an average of 40% reduction in root mean square position and orientation error in the two most common types of kinematic models for continuum manipulators, a Cosserat rod model and a pseudo-rigid body model.
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http://dx.doi.org/10.1109/lra.2020.2972880DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7050566PMC
April 2020

A Concentric Tube Robot System for Rigid Bronchoscopy: A Feasibility Study on Central Airway Obstruction Removal.

Ann Biomed Eng 2020 Jan 24;48(1):181-191. Epub 2019 Jul 24.

Mechanical Engineering Department, Vanderbilt University, Nashville, TN, USA.

New robotic systems have recently emerged to assist with peripheral lung access, but a robotic system for rigid bronchoscopy has yet to be developed. We describe a new robotic system that can deliver thin robotic manipulators through the ports of standard rigid bronchoscopes. The manipulators bend and elongate to provide maneuverability of surgical tools at the endoscope tip, without endoscope motion. We describe an initial feasibility study on the use of this system to bronchoscopically treat a central airway obstruction (CAO). CAO is prevalent and can be life-threatening in patients with large tumors, and conventional rigid bronchoscopic treatments place patients at risk of complications including broken teeth, neck trauma and damage to oropharyngeal structures due to significant forces induced by bronchoscope tilting and manipulation. In this study, we used an ex vivo ovine airway model to demonstrate the ability of a physician using the robotic system to efficiently remove tissue and restore the airway. Pre- and post-operative CT scans showed that the robot was able to reduce the degree of airway obstruction stenosis from 75 to 14% on average for five CAO resections performed in an ex vivo animal model. Using cadaver experiments, we demonstrated the potential of the robotic system to substantially reduce the intraoperative forces applied to the patient's head and neck (from 80.6 to 4.1 N). These preliminary results illustrate that CAO removal is feasible with our new rigid bronchoscopy robot system, and that this approach has the potential to reduce forces applied to the patient due to bronchoscope angulation, and thereby reduce the risk of complications encountered during CAO surgery.
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http://dx.doi.org/10.1007/s10439-019-02325-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6930337PMC
January 2020

Safe Motion Planning for Steerable Needles Using Cost Maps Automatically Extracted from Pulmonary Images.

Rep U S 2018 Oct 7;2018:4942-4949. Epub 2019 Jan 7.

Department of Computer Science, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

Lung cancer is the deadliest form of cancer, and early diagnosis is critical to favorable survival rates. Definitive diagnosis of lung cancer typically requires needle biopsy. Common lung nodule biopsy approaches either carry significant risk or are incapable of accessing large regions of the lung, such as in the periphery. Deploying a steerable needle from a bronchoscope and steering through the lung allows for safe biopsy while improving the accessibility of lung nodules in the lung periphery. In this work, we present a method for extracting a cost map automatically from pulmonary CT images, and utilizing the cost map to efficiently plan safe motions for a steerable needle through the lung. The cost map encodes obstacles that should be avoided, such as the lung pleura, bronchial tubes, and large blood vessels, and additionally formulates a cost for the rest of the lung which corresponds to an approximate likelihood that a blood vessel exists at each location in the anatomy. We then present a motion planning approach that utilizes the cost map to generate paths that minimize accumulated cost while safely reaching a goal location in the lung.
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http://dx.doi.org/10.1109/IROS.2018.8593407DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6519054PMC
October 2018

Can Elastic Instability be Beneficial in Concentric Tube Robots?

IEEE Robot Autom Lett 2018 Jul 1;3(3):1624-1630. Epub 2018 Feb 1.

Vanderbilt Department of Mechanical Engineering, Vanderbilt University, Nashville, TN USA.

Concentric tube manipulators exhibit elastic instability in which tubes snap from one configuration to another, rapidly releasing stored strain energy. While this has long been viewed as a negative phenomenon to be avoided at all costs, in this paper we explore for the first time whether the effect can be harnessed beneficially for certain applications. Specifically, we show that the energy released in an instability can be useful for challenging, high-force surgical tasks such as driving a needle through tissue. We use concentric tube models to define the energy released during elastic instability and experimentally evaluate a two-tube concentric manipulator that can drive suture needles through tissue by harnessing elastic instability beneficially.
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http://dx.doi.org/10.1109/LRA.2018.2800779DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6176742PMC
July 2018

Guiding Elastic Rods With a Robot-Manipulated Magnet for Medical Applications.

IEEE Trans Robot 2017 Feb 1;33(1):227-233. Epub 2016 Dec 1.

Department of Mechanical Engineering, Vanderbilt University, Nashville, TN 37235 USA, robert.

Magnet-tipped, elastic rods can be steered by an external magnetic field to perform surgical tasks. Such rods could be useful for a range of new medical applications because they do not require either pull wires or other bulky mechanisms that are problematic in small anatomical regions. However, current magnetic rod steering systems are large and expensive. Here, we describe a method to guide a rod using a robot-manipulated magnet located near a patient. We solve for rod deflections by combining permanent-magnet models with a Kirchhoff elastic rod model and use a resolved-rate approach to compute trajectories. Experiments show that three-dimensional trajectories can be executed accurately without feedback and that the system's redundancy can be exploited to avoid obstacles.
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http://dx.doi.org/10.1109/TRO.2016.2623339DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5722034PMC
February 2017

Through the Eustachian Tube and Beyond: A New Miniature Robotic Endoscope to See Into The Middle Ear.

IEEE Robot Autom Lett 2017 14;2(3):1488-1494. Epub 2017 Feb 14.

Department of Mechanical Engineering, Vanderbilt University, Nashville, TN 37235 USA.

This paper presents a novel miniature robotic endoscope that is small enough to pass through the Eustachian tube and provide visualization of the middle ear (ME). The device features a miniature bending tip previously conceived of as a small-scale robotic wrist that has been adapted to carry and aim a small chip-tip camera and fiber optic light sources. The motivation for trans-Eustachian tube ME inspection is to provide a natural-orifice-based route to the ME that does not require cutting or lifting the eardrum, as is currently required. In this paper, we first perform an analysis of the ME anatomy and use a computational design optimization platform to derive the kinematic requirements for endoscopic inspection of the ME through the Eustachian tube. Based on these requirements, we fabricate the proposed device and use it to demonstrate the feasibility of ME inspection in an anthropomorphic model, i.e. a 3D-printed ME phantom generated from patient image data. We show that our prototype provides > 74% visibility coverage of the sinus tympani, a region of the ME crucial for diagnosis, compared to an average of only 6.9% using a straight, non-articulated endoscope through the Eustachian Tube.
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http://dx.doi.org/10.1109/LRA.2017.2668468DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5708577PMC
February 2017

Characterization and Control of a Pneumatic Motor for MR-conditional Robotic Applications.

IEEE ASME Trans Mechatron 2017 Dec 1;22(6):2780-2789. Epub 2017 Nov 1.

Department of Mechanical Engineering, Vanderbilt University, Nashville, TN, 37212, USA.

Magnetic Resonance (MR) guided interventional robots have recently been developed for a variety of surgeries, such as biopsy, ablation, and brachytherapy. The actuators and encoders that power and track such robots must be MR-conditional. In this paper, we propose an MR-conditional pneumatic motor with an integrated and custom-built fiber-optical encoder that provides powerful and accurate actuation. The motor is coupled with a modular plastic gearbox that provides a variety of gear ratio options so that the motor can be adapted to application requirements. With a 100:1 gear reduction at 0.55 MPa, the motor achieves 460 mNm stall torque and 370 rpm no-load speed, which leads to the peak output power of 6W. The motor has the bandwidth of approximately 1.1 Hz and 3.5 Hz when connected to 8 m and 0.2 m air hoses, respectively. The motor was tested in a 3T MRI scanner. No image artifact was observed and maximum signal to noise ratio (SNR) variation was less than 5%. Different from most of the existing MR-conditional pneumatic actuators, the proposed motor shape is more like the traditional electric motors, which offers more flexibility in the MR-conditional robot design.
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http://dx.doi.org/10.1109/TMECH.2017.2767906DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6519483PMC
December 2017

Continuum Reconfigurable Parallel Robots for Surgery: Shape Sensing and State Estimation with Uncertainty.

IEEE Robot Autom Lett 2017 Jul 6;2(3):1617-1624. Epub 2017 Mar 6.

Department of Mechanical Engineering at Vanderbilt University, Nashville, TN 37235, USA.

This paper examines shape sensing for a new class of surgical robot that consists of parallel flexible structures that can be reconfigured inside the human body. Known as CRISP robots, these devices provide access to the human body through needle-sized entry points, yet can be configured into truss-like structures capable of dexterous movement and large force application. They can also be reconfigured as needed during a surgical procedure. Since CRISP robots are elastic, they will deform when subjected to external forces or other perturbations. In this paper, we explore how to combine sensor information with mechanics-based models for CRISP robots to estimate their shapes under applied loads. The end result is a shape sensing framework for CRISP robots that will enable future research on control under applied loads, autonomous motion, force sensing, and other robot behaviors.
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http://dx.doi.org/10.1109/LRA.2017.2678606DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5693261PMC
July 2017

Making Robots Mill Bone More Like Human Surgeons: Using Bone Density and Anatomic Information to Mill Safely and Efficiently.

Rep U S 2016 Oct 1;2016:1837-1843. Epub 2016 Dec 1.

Department of Mechanical Engineering, Vanderbilt University, Nashville, TN USA.

Surgeons and robots typically use different approaches for bone milling. Surgeons adjust their speed and tool incidence angle constantly, which enables them to efficiently mill porous bone. Surgeons also adjust milling parameters such as speed and depth of cut throughout the procedure based on proximity to sensitive structures like nerves and blood vessels. In this paper we use image-based bone density estimates and segmentations of vital anatomy to make a robot mill more like a surgeon and less like an industrial computer numeric controlled (CNC) milling machine. We produce patient-specific plans optimizing velocity and incidence angles for spherical cutting burrs. These plans are particularly useful in bones of variable density and porosity like the human temporal bone. They result in fast milling in non-critical areas, reducing overall procedure time, and lower forces near vital anatomy. We experimentally demonstrate the algorithm on temporal bone phantoms and show that it reduces mean forces near vital anatomy by 63% and peak forces by 50% in comparison to a CNC-type path, without adding time to the procedure.
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http://dx.doi.org/10.1109/IROS.2016.7759292DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5558793PMC
October 2016

Optimization of Curvilinear Needle Trajectories for Transforamenal Hippocampotomy.

Oper Neurosurg (Hagerstown) 2017 02 25;13(1):15-22. Epub 2016 Jul 25.

Department of Mechanical Engineering, Vanderbilt University, Nashville, Tennessee.

Background: The recent development of MRI-guided laser-induced thermal therapy (LITT) offers a minimally invasive alternative to craniotomies performed for tumor resection or for amygdalohippocampectomy to control seizure disorders. Current LITT therapies rely on linear stereotactic trajectories that mandate twist-drill entry into the skull and potentially long approaches traversing healthy brain. The use of robotically-driven, telescoping, curved needles has the potential to reduce procedure invasiveness by tailoring trajectories to the curved shape of the ablated structure and by enabling access through natural orifices.

Objective: To investigate the feasibility of using a concentric tube robot to access the hippocampus through the foramen ovale to deliver thermal therapy and thereby provide a percutaneous treatment for epilepsy without drilling the skull.

Methods: The skull and both hippocampi were segmented from dual CT/MR image volumes for 10 patients. For each of the 20 hippocampi, a concentric tube robot was designed and optimized to traverse a trajectory from the foramen ovale to and through the hippocampus from head to tail.

Results: Across all 20 cases, the mean distances (error) between hippocampus medial axis and backbone of the needle were 0.55 mm, 1.11 mm, and 1.66 mm for best, mean, and worst case, respectively.

Conclusion: These curvilinear trajectories would provide accurate transforamenal delivery of an ablation probe to typical hippocampus volumes. This strategy has the potential to both decrease the invasiveness of the procedure and increase the completeness of hippocampal ablation.
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http://dx.doi.org/10.1227/NEU.0000000000001361DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5453508PMC
February 2017

In vivo measurement of vocal fold surface resistance.

Laryngoscope 2017 10 2;127(10):E364-E370. Epub 2017 Jun 2.

Department of Otolaryngology.

Objectives/hypothesis: A custom-designed probe was developed to measure vocal fold surface resistance in vivo. The purpose of this study was to demonstrate proof of concept of using vocal fold surface resistance as a proxy of functional tissue integrity after acute phonotrauma using an animal model.

Study Design: Prospective animal study.

Methods: New Zealand White breeder rabbits received 120 minutes of airflow without vocal fold approximation (control) or 120 minutes of raised intensity phonation (experimental). The probe was inserted via laryngoscope and placed on the left vocal fold under endoscopic visualization. Vocal fold surface resistance of the middle one-third of the vocal fold was measured after 0 (baseline), 60, and 120 minutes of phonation. After the phonation procedure, the larynx was harvested and prepared for transmission electron microscopy.

Results: In the control group, vocal fold surface resistance values remained stable across time points. In the experimental group, surface resistance (X% ± Y% relative to baseline) was significantly decreased after 120 minutes of raised intensity phonation. This was associated with structural changes using transmission electron microscopy, which revealed damage to the vocal fold epithelium after phonotrauma, including disruption of the epithelium and basement membrane, dilated paracellular spaces, and alterations to epithelial microprojections. In contrast, control vocal fold specimens showed well-preserved stratified squamous epithelia.

Conclusions: These data demonstrate the feasibility of measuring vocal fold surface resistance in vivo as a means of evaluating functional vocal fold epithelial barrier integrity. Device prototypes are in development for additional testing, validation, and for clinical applications in laryngology.

Level Of Evidence: NA Laryngoscope, 127:E364-E370, 2017.
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http://dx.doi.org/10.1002/lary.26715DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5607073PMC
October 2017

Pre-operative Screening and Manual Drilling Strategies to Reduce the Risk of Thermal Injury During Minimally Invasive Cochlear Implantation Surgery.

Ann Biomed Eng 2017 Sep 18;45(9):2184-2195. Epub 2017 May 18.

Department of Otolaryngology, Vanderbilt University Medical Center, 1215 21st Ave. South, MCE 10450, South Tower, Nashville, TN, USA.

This article presents the development and experimental validation of a methodology to reduce the risk of thermal injury to the facial nerve during minimally invasive cochlear implantation surgery. The first step in this methodology is a pre-operative screening process, in which medical imaging is used to identify those patients that present a significant risk of developing high temperatures at the facial nerve during the drilling phase of the procedure. Such a risk is calculated based on the density of the bone along the drilling path and the thermal conductance between the drilling path and the nerve, and provides a criterion to exclude high-risk patients from receiving the minimally invasive procedure. The second component of the methodology is a drilling strategy for manually-guided drilling near the facial nerve. The strategy utilizes interval drilling and mechanical constraints to enable better control over the procedure and the resulting generation of heat. The approach is tested in fresh cadaver temporal bones using a thermal camera to monitor temperature near the facial nerve. Results indicate that pre-operative screening may successfully exclude high-risk patients and that the proposed drilling strategy enables safe drilling for low-to-moderate risk patients.
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http://dx.doi.org/10.1007/s10439-017-1854-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5694393PMC
September 2017

Toward Transoral Peripheral Lung Access: Combining Continuum Robots and Steerable Needles.

J Med Robot Res 2017 Mar 11;2(1). Epub 2016 Oct 11.

Mechanical Engineering, Vanderbilt University, Nashville, TN 37235, USA.

Lung cancer is the most deadly form of cancer in part because of the challenges associated with accessing nodules for diagnosis and therapy. Transoral access is preferred to percutaneous access since it has a lower risk of lung collapse, yet many sites are currently unreachable transorally due to limitations with current bronchoscopic instruments. Toward this end, we present a new robotic system for image-guided trans-bronchoscopic lung access. The system uses a bronchoscope to navigate in the airway and bronchial tubes to a site near the desired target, a concentric tube robot to move through the bronchial wall and aim at the target, and a bevel-tip steerable needle with magnetic tracking to maneuver through lung tissue to the target under closed-loop control. In this work, we illustrate the workflow of our system and show accurate targeting in phantom experiments. Ex vivo porcine lung experiments show that our steerable needle can be tuned to achieve appreciable curvature in lung tissue. Lastly, we present targeting results with our system using two scenarios based on patient cases. In these experiments, phantoms were created from patient-specific computed tomography information and our system was used to target the locations of suspicious nodules, illustrating the ability of our system to reach sites that are traditionally inaccessible transorally.
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http://dx.doi.org/10.1142/S2424905X17500015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5415307PMC
March 2017

Coffee: the key to safer image-guided surgery-a granular jamming cap for non-invasive, rigid fixation of fiducial markers to the patient.

Int J Comput Assist Radiol Surg 2017 Jun 30;12(6):1069-1077. Epub 2017 Mar 30.

Department of Mechanical Engineering, Vanderbilt University, Nashville, TN, USA.

Purpose: Accurate image guidance requires a rigid connection between tracked fiducial markers and the patient, which cannot be guaranteed by current non-invasive attachment techniques. We propose a new granular jamming approach to firmly, yet non-invasively, connect fiducials to the patient.

Methods: Our granular jamming cap surrounds the head and conforms to the contours of the patient's skull. When a vacuum is drawn, the device solidifies in a manner conceptually like a vacuum-packed bag of ground coffee, providing a rigid structure that can firmly hold fiducial markers to the patient's skull. By using the new Polaris Krios optical tracker, we can also use more fiducials in advantageous configurations to reduce registration error.

Results: We tested our new approach against a clinically used headband-based fiducial fixation device under perturbations that could reasonably be expected to occur in a real-world operating room. In bump testing, we found that the granular jamming cap reduced average TRE at the skull base from 2.29 to 0.56 mm and maximum TRE at the same point from 7.65 to 1.30 mm. Clinically significant TRE reductions were also observed in head repositioning and static force testing experiments.

Conclusion: The granular jamming cap concept increases the robustness and accuracy of image-guided sinus and skull base surgery by more firmly attaching fiducial markers to the patient's skull.
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http://dx.doi.org/10.1007/s11548-017-1569-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6252059PMC
June 2017

Cadaveric Testing of Robot-Assisted Access to the Internal Auditory Canal for Vestibular Schwannoma Removal.

Otol Neurotol 2017 03;38(3):441-447

*Mechanical Engineering †Otolaryngology, Vanderbilt University Medical Center ‡Electrical Engineering, Vanderbilt University, Nashville, Tennessee.

Hypothesis: An image-guided robotic system can safely perform the bulk removal of bone during the translabyrinthine approach to vestibular schwannoma (VS).

Background: The translabyrinthine approach to VS removal involves extensive manual milling in the temporal bone to gain access to the internal auditory canal (IAC) for tumor resection. This bone removal is time consuming and challenging due to the presence of vital anatomy (e.g., facial nerve) embedded within the temporal bone. A robotic system can use preoperative imaging and segmentations to guide a surgical drill to remove a prescribed volume of bone, thereby preserving the surgeon for the more delicate work of opening the IAC and resecting the tumor.

Methods: Fresh human cadaver heads were used in the experiments. For each trial, the desired bone resection volume was planned on a preoperative computed tomography (CT) image, the steps in the proposed clinical workflow were undertaken, and the robot was programmed to mill the specified volume. A postoperative CT scan was acquired for evaluation of the accuracy of the milled cavity and examination of vital anatomy.

Results: In all experimental trials, the facial nerve and chorda tympani were preserved. The root mean squared surface accuracy of the milled cavities ranged from 0.23 to 0.65 mm and the milling time ranged from 32.7 to 57.0 minute.

Conclusion: This work shows feasibility of using a robot-assisted approach for VS removal surgery. Further testing and system improvements are necessary to enable clinical translation of this technology.
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http://dx.doi.org/10.1097/MAO.0000000000001324DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5303146PMC
March 2017
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