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  • RESEARCH STRATEGY SIGNIFICANCE: There is broad consensus that (a) the future of minimally invasive surgery lies in naturalorifice/single port access and that (b) robotics is the key technology to bring us to this future. Our group haspioneered single-port robotic subxiphoid interventions on the beating heart since 2001 . Other teleroboticmechanisms have been developed for reaching inside confined surgical spaces though a single port: snakerobots , wireless surgical capsules, inchworm robots (such as our own Heartlander ), and flexible needles .Several of these mechanisms are only capable of monitoring confined surgical spaces , or injecting drugs . Weadvocate the use of snake robots because can reach inside confined surgical spaces through a smallsingle port and can perform surgical tasks. As Taylor described , a robotic instrument for minimally invasive surgery (MIS) must have sufficientdexterity, strength, and accuracy for its intended use. Both complex tissue manipulation (e.g. deforming,dissecting, suturing, etc.) and navigation require tip dexterity, especially in confined surgical spaces. Tissuemanipulation requires the “right” amount of strength, i.e., stiffness, at the tip: low tip stiffness may not besufficient to manipulate tissue, whereas high tip stiffness runs the risk of damaging delicate tissues whilenavigating to a target site. Therefore it is critical to modulate the stiffness of the tip of a surgical snakerobot according to the surgical task and the location of the tip. Unfortunately, either snake robots havehigh stiffness and low dexterity, such as the serpentine robots consisting of a series of rigid links[43], or theyhave high dexterity and low stiffness ., such as the continuum robots whose flexible tubular structuresassume the shape of smooth curve whose entire curvature can be controlled (). Continuum robots includesteerable catheters , super elastic backbone robots and concentric tube steerable cannula . Our group has a vastexperience in building snakerobots on both sides of thespectrum. The highly articulatedrobotic probe (HARP) developedby our group for MIS (-left) is aserpentine robot with 30 links andthe outside diameter of 11mm. Figure 1: (left) HARP (right) Steerable cannulaThe HARP can have any desired curve with minimum radius of curvature of 35mm. A key feature of the HARPis that it uses conventional actuation, unlike other research platforms based on shape memory alloy actuators., which suffer from a slow response time, low contact force, and excessive heat The HARP has beendemonstrated in 30 pigs, 2 cadavers and 3 live humans [CITE]. Since the HARP is made of rigid links, it hashigh stiffness but low dexterity. On the other hand, we have developed steerable cannulas that provide high tipdexterity inside confined spaces, but alas, by design are flexible and therefore have limited strength. Wehypothesize that, in order to enable complex single-port procedures in hard-to-reach locations inside the body(e.g. epicardial interventions on the beating heart), the introduction of snake robots with high dexterity andsufficient stiffness may provide an elegant solution. Hence, our proposal addresses a critical barrier toprogress in the field of robotic surgery. Constructing the mechanism, however, is not enough. The physician requires a sense of awareness of theoperating site in order to both access it and deliver therapies. Direct video assistance has limited role fornavigation in virtual spaces (e.g. pericardial sac) due to the confined physical space. Conventional image-guidance techniques for MIS provide minimal information to the user: they are most often limited to either 1) 2Dprojective views of the operation, such as fluoroscopy [CITE], 2) a simplified rendered visualization that showsa tracking device registered to preoperative images [CITE], or 3) a fusion of ultrasound with 3D reconstructedimages [CITE]. All of these methods are limited in the amount of information that can be conveyed to thesurgeon. These existing methods can also be inaccurate and unintuitive to use during a surgical operation. Webelieve that MIS would benefit from a new image-guidance method that fuses multiple sensing modalities,that estimates the inherent motion of internal organs, and that incorporates constraints imposed on therobot’s path in a stochastic filtering framework, all while simplifying the graphical interface. Showing theprecise location and shape of the surgical robot in relation to a 4D 3D rendered anatomical target would beinvaluable for planning and feedback. The 34D modeklmodel, specifically, would provide a more accurate viewof the operating site. Therefore, image-guided snake robots will provide a truly elegant solution.
  • As an exemplary application of single port intervention that requires asnake robot with high dexterity and sufficient stiffness, we propose tofocus the current research proposal on radiofrequency (RF) ablation for atrialfibrillation (AF). AF is the most common cardiac arrhythmia affecting >4 millionAmericans, leading to death, stroke, heart failure and reduced quality of life. Anovel minimally invasive epicardial ablation approach has been introducedand results in 94% freedom from recurrent AF without anti arrhythmic drugs.However, this procedure has limited application because it requires bilateralsequential thoracoscopic approach with 4-5 ports on each side of the chest,sequential deflation and reinflation of the ipsilateral lung and significantpotential for complications. The procedure is based on the “Dallas lesion set” Figure 2: Five Box Mazeconcept (, ) creating RF lesions limited to the left atrium and superior venacava (SVC). The entire procedure is confined within the boundaries of the pericardial space on the beatingheart and could be achieved more simply from a single subxiphoid port with a snake robot with both highdexterity and stiffness; the goal is to replicate the function of the soft-tip endo-kitner retractor (labeled R)depicted in Figure 2: Five Box Maze and necessary for blunt dissection of the pericardial reflections and allowsimultaneous exposure and ablation of target regions of the left atrium by delivery of RF energy. To performthe Five Box Maze, critical areas of the extrapericardial left atrium need to be dissected bluntly fromthe pericardial reflection and contiguous ablation lesions need to be created. The ability to perform aDallas lesion set through a single port would amount to a breakthrough in the cure of AF. A snake robot with high dexterity and stiffness will also allow new minimally invasive intracardiacprocedures. In addition, additional non-cardiac procedures in confined spaces where interactions with thetissue and the device are required will be enabled. For instance, video-assisted thoracic surgery (VATS)robotic lobectomy and mediastinoscopy require complex dissection of the hilum of the lung and mediastinum.Trans-oral robotic surgery (TORS) will also benefit from such a hybrid snake robot . Successful completion ofour proposed project will therefore introduce novel technologies that will be leveraged to advance other fields. INNOVATION: To overcome the challenges of the proposed exemplary application, we plan to develop aneasy-to-use novel image-guided hybrid snake robot that simultaneously provides tip dexterity andstiffness when it interacts with tissue, while all along providing the physician a real-timeSOMETHINGthree-dimensional view of the target location from any perspective. We will achieve thisambitious goal through three aims: Aim 1: We propose to combine, for the first time in this field, two types of snake robots: the HARP and asteerable cannula. The steerable cannula enhances the tip dexterity and allows reaching very tight spacesbecause of the small size. The HARP operates as stiff sheath for the steerable cannula so it significantlyincreases the tip stiffness of the steerable cannula. The hybrid snake promises the ability to follow a pre-planned arbitrary three dimensional curve and also the ability to perform dexterous contact tasks insidecomplex surgical environments. Aim 2: We will also develop advanced path planners and tip controllers to exploit these unique abilitiesof the hybrid snake. Our path planners and tip controllers will allow safe navigation of the robot insidepericardium space while the robot tip can be in contact. The novelty of this approach will lie in our controller’sability to modulating tip stiffness of the robot so we can set a low tip stiffness during navigating near delicatetissues and a high stiffness during blunt dissection. The planners will exploit this capability to coordinate bothmechanisms, the HARP and the steerable cannula, as if they are one Aim 3: We will design and implement a completely new method of image-guidance using electromagneticposition sensors on the robot projected over the left atrial surface mesh segmented from preoperativecomputerized tomography. This will allow safe and targeted performance of the task around the beating heart.This requires a new paradigm in image-guidance for MIS to obtain a more accurate and representative modelof the operating site. In our opinion, the core enabling technology will be simultaneous localization andmapping (SLAM). SLAM is the task of having a robot build a map of its surrounding environment whilesimultaneously estimating its relative pose in that map. While SLAM has been investigated for wheeled mobilerobots , we will be among the first to introduce and advance its explicit use for surgical robots. Wepropose SLAM for MIS that uses a stochastic filtering method, based on Kalman filtering, to continually correctsurface models and estimate the motion of internal organs. Our SLAM algorithm will combine differentmodalities (vision, a magnetic tracking system and preoperative CT) to localize the robot as accurately aspossible. We believe the use of SLAM with surgery will ultimately improve the accuracy of navigation for MIS
  • and will speed up operation times. This goes beyond the recent introduction of monte carlo localizationtechniques , in that we are performing motion estimation of the anatomical surfaces. We believe that the use ofSLAM will allow MIS to be adopted by surgeons who normally resist the use of MIS. This is because SLAM willrecover the “bird’s eye” view of the operating field to which surgeons have been accustomed. Finally, theSLAM algorithms developed in the proposed work are general to all procedures, and general to other roboticapplications outside of the medical robotics field; this is truly a fundamental breakthrough. We identified as the critical task blunt dissection, defined as a surgical technique used to gently separatetissues while avoiding injury to important nearby structures such as blood vessels or nerves. We believe thatthe hybrid snake will enable blunt dissection of pericardial reflections around the left atrium leading to a singleport Dallas lesion set for cure of AF.RESEARCH APPROACH:Progress Report (a) HARP Mechanism A BDevelopment and Experiments. From June2006 to present (October 2010), the SpecificAims of the previously awarded R01 grant weresuccessfully achieved. We completed thedevelopment of the 11 mm Highly ArticulatedRobotic Probe (HARP) prototype forintrapericardial navigation and cardiactherapeutics delivery and technical details have Feeder Probebeen described elsewhere . (Figure 3). A feedingmechanism, rigidly attached to the operatingroom table via an adjustable support mechanism,inserts the HARP through a small incision or port.The feeder supplies two additional degrees of Cfreedom to regulate forward and reverse motion. DIn total, the HARP has 102 degrees of freedom Figure 3: (a) HARP is mounted on a surgical table and a (c) The HARP is sometimes called a “follow- feeder pushes the HARP out to follow (b,d) complex pathsthe-leader” mechanism in that it can follow atortuous path in three dimensions (Figure 4). It achieves this motion because of its unique concentric structurewhere an inner and outer mechanism alternate between being rigid and limp to generate a curve. Initially, theouter mechanism is made limp and advances forward. Meanwhile, the inner mechanism remains rigid andhence serves as a guide for outer mechanism. As the outer mechanism moves beyond the innte, it “steers” itsdistal portion. Subsequently, the outer mechanism is made rigid, the inner mechanism is made limp, the innermechanism advances until it “catches up” to the outer mechanism, and the procedure repeats. The HARP trulyis state of the art; it is innovative because it achieves the follow-the-leader motion with no exotic actuationtechnology, making it more maneuverable, robust, and reliable, all of which are important for carrying theconcept to clinical use. Finally, the HARP has three working channels through which conventional tools can be advanced as wellas other novel devices such as the steerable cannulas (Figure 5). In our experiments, we have used thesechannels to house an ablation and mapping catheter up to 8 French in outside diameter, small fiberopticcameras, biopsy forceps, and suction. Figure 4: Probe leaving a feeder and then advancing around a heart model. This figure illustrates navigation aroundthat heart which is not possible with a laparoscope or endoscope. The probe is an innovative design that usesconventional actuation technology, an innovative feature the NOTES robotics system will also have.We successfully tested the HARP in an anthropomorphic beating heart phantom, in a porcine model in vivo,and in human cadavers. We also tested and confirmed the hypothesis that the HARP is superior to existing
  • dedicated rigid technology for subxiphoidvideopericardioscopy . In a recent study, weperformed animal experiments comparing acommercially available subxiphoidvideopericardioscopy system (SVP)(FlexView System, Guidant Cardiac Surgery)as a control (n=5) to the HARP in the closed-chest porcine preparation (n=5 in eachgroup) . Multiple hemodynamic parameterswere recorded during the testing. Unstablehemodynamics and fatal arrhythmia wereobserved during the trials using the rigid Figure 5: HARP has three channels for passing toolsFlexView SVP device but we did not observeany occurrence of significant arrhythmia andunstable hemodynamics using HARP. The HARP was able to successfully navigate through the epicardialspace of the beating heart from a single subxiphoid port to all 6 deep intrapericardial anatomical targets thatwere preselected via 7 distinct routes. Our study demonstrates the superiority of the HARP, with regard tonavigation through the pericardial space to interventional targets on the epicardium, using image guidancealone. These findings suggest that such highly articulated systems may achieve similar improvements overrigid techniques with regard to patient safety during intrapericardial procedures in human patients. (b) Kinematic Modeling and Control We have substantial experience on kinematic modeling, design andcontrol of steerable cannulas . We used Cosserat rod theory to model large deformation of the steerablecannula during contact. For robotic tasks that involve interaction with an environment, stiffness control shouldbe superior to position control. In stiffness control, we are the first to establish a robust relation between theenvironment force and the tip of a continuum robot This controller was demonstrated experimentally for asteerable cannula interacting with a soft environment. The steerable cannula consisted of two pre-curved NITitubes of 15cm Figure 6a. An EM tracker was used to measure the tip position of the robot Figure 6b. Resultsshowed that the stiffness controller can modulate the tip stiffness (Figure 6c.), provide good dynamicperformance and exhibit stability during contact transitions. (a) (b) (c) Figure 6: Stiffness control of a steerable cannula (a) the tubes of the steerable cannula (b) the experimental setup wand EM tracker sensor (c) tip stiffness curves of steerable cannula for three different desired stiffnesses (c) Identification of design constraints for Hybrid Snake Robot (unpublished preliminarily results) The hybrid snake we propose is composed of a HARP and a steerable cannula as shown in In ourpreliminary work, we identified the required strength for the HARP to accept a steerable cannula. The strengthof the HARP should be high enough to be able to sustain the bending moment M caused by the steerablecannula. The bending moment caused by a straight steerable cannula when it is deformed to the radius of D3curvature R is M = 0.26 E T where E is the Youngs modulus of the tubes of the steerable cannula, D is the Rnominal diameter of the steerable cannula, and T is the thickness of cannula. The maximum moment that theHARP can withstand is M = rµFc where Fc is the cable tension, µ is the friction coefficient of the joint of theHARP and r is the radius of the HARP joint . As a result, the HARP can sustain the cannula moment if
  • D3rµFc ≥ 0.26 E T . We evaluated this equation for the current HARP and a steerable Rcannula consisting of NiTi Tubes of 1.118 x 1.041 mm and 0.914 x 0.813mm Figure 7.The experimental results showed that the current HARP can deform the straight cannulato the radius of the curvature of 8.7 cm. Given the radius of curvature of the HARP issmaller than 8.7cm, this suggests that the HARP needs to be made stronger. (d) Previous work for Simultaneous Localization and Mapping (SLAM): As aresearch group, we are building upon years of previous SLAM research to solve novelestimation problems. SLAM has largely been a navigation technology developed formobile robots, and more recently free-flying rotor craft and AUVs [Ref from HowieSteve]. Our work in estimation and filtering has advanced the SLAM field in three key Figure 7: Steerableways 1) robotic mapping with simple cameras (Tully 08), 2) mapping on a topological cannula passinggraph (Tully 09), and 3) localization for wheeled mobile robots (Tully 07). Our past through a working channel of the HARP.experience in SLAM, combined with our expertise in snake robotsmakes us uniquely qualified to advance and extend SLAM to medicalrobotics. Already, we have begun to extend filtering and estimation tothe HARP surgical robot. Our work, thus far, has involved performingstate estimation and using stochastic models to estimate the mostlikely shape of the snake robot based on fusing information from themeasured drive cable lengths and a position measurement from an EMtracker. We have also performed 3D reconstruction and registration todraw the snake robot location for image-guidance. This implementationhas been used in our porcine preparation. An example result is shownin Figure 8. This preliminary work did not include the more advancedmotion estimation that SLAM will provide. Figure 8: previous work on filtering for snake shape estimation and 3D SPECIFIC AIM #1: Design and develop a hybrid snake robot by reconstructionintegrating the HARP and the steerable cannula, via Sub-Aim #1.1:Develop a steerable cannula to be mounted inside the HARP to enable desiredtissue dissection and ablation tasks Sub-Aim #1.2: Adapt the HARP’s unique linkdesign and enhance its strength shape to accept the steerable cannula.
  • Sub-Aim #1.1: Develop a steerable cannula to be mounted inside the articulated probe to enable desired tissue dissection tasks: We will design the steerable cannula of the hybrid snake such that it can perform two distinct tasks required for the Five Box Left Atrial Maze procedure : 1) blunt dissection of pericardial reflections ( and Figure 10) and 2) ablation of the five box maze left atrial pattern (Figure 11). The four target pericardial reflections that require blunt dissection by the hybrid snake are (see Figure 10): Blunt dissection of the four locations of pericardial reflections is required in order for the hybrid snake to be able to complete the maze ablation pattern. Successful dissection of reflection 1 will Figure 9: Pericardial be defined by the ability of the entire hybrid reflections (posterior view). Areas in white indicate snake to advance through the dissectedFigure 10: Hybrid snake must dissect “extrapericardial” left atrium. path. For reflections 2, 3 and 4 (see Figurefour spots of pericardium1) reflectionbetween the right inferior pulmonary vein 10), the success will be defined as the Figure 11: Five box maze(RIPV) and the inferior vena cava (IVC); advancement of the tip of the steerable2) reflection between the right superior cannula past the anatomical boundaries of the reflection. We showedpulmonary vein (RSPV) and the right in the Table 1 the average distances between pulmonary veins, thepulmonary artery (RPA); 3) reflection IVC and the pulmonary veins and the diameters of the veins for fivebetween the left superior pulmonary vein patients. We will consider these dimensions in designing our steerable(LSPV) and the left pulmonary artery cannula. For the blunt dissection, the steerable cannula should be able(LPA) and 4- reflection over the superior to make an up-and-down straight sweep motion when it pushes againstvena cava. the pericardium sack at each dissection location to perform bothablation and dissection.Diameter Average Range We will consider two preliminary designs for the steerable cannula.LSPV 16mm 13-20mm Our goal for the first design is to maximize the tip stiffness. High tipLIPV 17mm 13-19mm stiffness is required for performing blunt dissection and tissue retraction.RSPV 19mm 15-20mm Our goal for the second design is to maximize the tip dexterity by addingRIPV 16mm 12-21mm additional tip orientation control.Distance Average Range Design #1: This design will consist of two curved tubes of the sameLSPV-LIPV 5mm 3-8mm length, initial curve, and bending stiffness. The tubes will consist of twoRSPV-RIPV 7mm 5-10mm constant curvature segments: 1) a long straight segment which is longerIVC to RIPV 20mm 17-40mm than the length of the articulated probe and 2) a short curved section which is long enough to provide sufficient tip displacement for the intended task. Table 1: measured value for 5 patients The outer and inner diameters of both tubes are selected such that theycan be inserted inside each other and the combinationcan be inserted inside the port of the HARP. We refer tothe combination of two tubes as combined tube. Byrotating two tubes with respect to each other, thecurvature of the curved segment of the combined tubevaries from zero (straight configuration) to a maximumcurvature. When the combined tube is inserted into theHARP, the straight portion takes the shape of the HARP.The combined tube can also extend and rotate insidethe HARP and the orientation of its distal portion can bechanged by the last link of the HARP. Figure 12: The design 1 and 2 for the steerable Design #2. This design will consist of three curved cannulatubes. Two of the tubes will be similar to the tubes of the first design. The third tube also consists of a straightsegment and a curved segment. Comparing with two first tubes, the third tube has a longer straight segment,the radius of the curvature of its curved distal end is smaller, and its bending stiffness is much smaller. Thethird tube is inserted inside two first tubes. When the third tube is retracted, it conforms to the shape of thecombination of the first two tubes. When it is extended, the curved segment relaxes to its original curvature.The second design provides additional tip orientation control and distal dexterity.
  • Both designs significantly increase the tipdexterity of the hybrid snake in comparison to theHARP alone. Figure 13: illustrating the curves andsweep tip motions achievable with the HARP alonevs. the hybrid snake. The hybrid snake (with tubesof 2mm) allows a longer tip displacement (8cm vs.1cm) and a smaller radius of curvature (1cm vs.4.5cm). The hybrid snake can go inside smallerspaces at its distal end (0.2cm vs. 1.2 cm). Choice of material. We will construct our tubesfrom NiTi (Ni-Ti Tubes Inc, Fremont, CA). These Figure 13: comparing distal dexterity of hybrid snake and HARPtubes are super‐elastic and biocompatible. The minimum achievable radius of curvaturefor a NiTi tube is a function of tube outer diameter. The minimum achievable radius ofcurvature is 5mm for a tube of 1 mm diameter and 12.5 mm for a tube of 2.5mm. We willuse heating and quenching process to manufacture our curved tubes . Each tube iscurved to desired shape and it is shape hold by a fixture. The fixture and the tubes arethen heated in a high temperature oven and water quenched. Figure 14: endo-kitner For intended tasks such as blunt dissection, retraction and ablation, we willmodify the steerable cannula with addition of an atraumatic end (similar to endo-kitner,Figure 14) . For large tools (up to 8 French), we can advance them (e.g. radiofrequency ablationcatheters or ICE) through the working port of the HARP and use the steerable cannula to navigate them. Forsmaller tools we can use the lumen of the steerable cannula itself. Sub-Aim #1.2: Adapt the HARP’s unique link design and enhance its strength to accept steerablecannula: In our work during the previous NIH grant support period, the highly articulated probe had only beenintended to carry highly flexible catheter-like devices. Because these types of catheter tools have beendesigned for specific applications (which are endoluminal in nature), they lack the qualities to make themuseful for additional extended tasks in other environments. The introduction of steerable cannulas presentsan interesting and necessary set of functionalities which stem from a combination of dexterity and strength.However, unlike highly flexible catheter devices, steerable cannulas provide a level of stability and strengthorders of magnitude beyond their catheter-like counterparts. In our preliminary work (last section) weevaluated the bending moment induced by the steerable cannula on the HARP. The HARP should be strong enough to sustain not only the bending moment induced by the steerablecannula but also the torque caused by the HARP weight and the tip load. The maximum moment caused bythe HARP weight, W, and the external load F, is τ = L(W / 2 + F ) where L is the length of the HARP. Themaximum moment that the HARP can generate is M = rµFc where Fc is the cable tension, µ is the frictioncoefficient of the joint of the HARP and r is the radius of the HARP joint . This proposal identifies three ways inwhich the HARP can be made stronger: material properties of the links, transmission cables and their drivingmotors, and increasing joint sizes. We will evaluate different materials for the links in the probe so that theycan withstand higher compressive loads as well as improve the frictional characteristics which are critical to theperformance of the HARP. While the specific material is yet to be determined, it is clear that a move to metalparts will improve intrinsic material strength as well as improve the coefficient of friction by 50% . Likewise, wewill consider other cables but will start with braided stainless steel cable or Aramid cable because they allow amuch larger transmission force. This also requires having larger motors or larger gear ratios. We will build anew HARP that has the required strength. Finally, the hybrid snakewill naturally require a newfeeder. This portion of the work isstraightforward engineeringwhich will simply integrate thecurrent HARP feeder with thefeeder for a steerable cannula(Figure 15:). Our group is already Figure 15: The feeder for the HARP and the feeder for a steerable cannula
  • well-poised to develop both the mechanism and control electronics architecture, leveraging our experiencefrom the previous R01 support. SPECIFIC AIM #2 Develop control and path planning for the hybrid snake robot, via Sub-Aim #2.1:Kinematic modeling and position control, Sub-Aim #2.2: hybrid position-stiffness control and Sub-Aim #2.3:path planning. A kinematic model is needed in order to precisely control the position or the stiffness of the tip of thehybrid snake. The kinematic model calculates the mapping between the tip configuration of the snake and therotational angles of the motors of the snake. Without the kinematic model, it is impossible for the physician toprecisely teleoperate the hybrid snake. We have developed separate kinematics models and controllers forthe HARP and the steerable cannula. We will combine these models and controllers to control the hybridsnake. The overall kinematic model of the hybrid snake is decomposed into the product of the unloadedkinematic models of the HARP and the steerable cannula, and a deformation model that calculates thebending of the hybrid snake due to the applied loading. We will use the Cosserat theory for curved rods toobtain the deformation of the snake. We extended the Cosserat rod theory to model large deformation ofprecuved tubes when they interact with each under external loading . A path planner is needed to coordinate the internal degrees of freedom of the hybrid snake to producedesired motions. Without a path planner, the physician would have to individually control each joint in thehybrid snake, which is an impossible, let alone unrealistic, task for the physician. Here, we will build upon thekinematic models developed in the previous subaims, to develop the theory, and then the software, whichallows the physician to specifiy high-level directives and have the computer perform the necessarycomputations to carry out these objectives. This path planner will offset much of the cognitive load placed onthe surgeon during a procedure allowing the physician to focus on important high-level decisions. Sub-Aim #2.1: kinematic modeling and position control: We will develop a “two state” control for thehybrid snake. The controller at its “first state” will bring only the HARP to the targeted position and then at thesecond state will control the position of the tip of the steerable cannula. We will use a phantom haptic device(Sensible Inc. MA) to teleoperate the HARP using the “follow-the-leader” approach . After the HARP reachesthe intended configuration, we will lock the articulated probe at its position and then use the phantom device tocontrol the position of the steerable cannula tip. We will use the unloaded kinematic model of the steerablecannula to control its tip. The unloaded kinematic model is obtained by using functional approximation ofmeasured data . Our main goal at this stage is to optimize the design of the hybrid snake, the bandwidth of itsactuators and the accuracy of the unloaded kinematic model. We will test the hybrid snake and its controller onphantom animal models at the end of this sub-aim. Sub-Aim #2.2: hybrid position-stiffness control: We will develop a hybrid position-stiffness controller tocontrol both the tip stiffness and tip configuration of the hybrid snake. The hybrid stiffness controller will allowthe surgeon to modulate the tip stiffness of the hybrid snake. The surgeon can set a high tip stiffness duringblunt dissection and set a low stiffness when the snake tip approaches delicate tissues such as blood vessels.The stiffness controller will be very useful for performing blunt dissection of the pericardium reflections for thefive box maze procedure. The physician can set a high tip stiffness when the tip of the snake is at the center ofthe marked dissection spots (Figure 10) and far from the pulmonary veins. The physician can set a low tipstiffness when the snake tip is close to the pulmonary veins. To implement the stiffness controller, we will usetwo EM trackers to measure the tip positions of the steerable cannula and the HARP. The outputs of these twosensors will then be used to calculate the deflection of the tip of the snake, the tip force, and the tip stiffness. Ifthe measured tip stiffness of the hybrid snake is less than desired, the controller will advance the tip of thesnake toward the tissue to increase the contact stiffness. If the measured stiffness is too high, the controller willmove back the snake to reduce the applied force on the tissue and the tip stiffness. We will use the hybrid stiffness controller to implement haptic feedback for the hybrid snake. In general, itis difficult to implement haptic feedback for a surgical robot due to the difficulty of using force sensor at the tipof the robot. However, it is possible to measure the tip force of the hybrid snake from the deflection of itssteerable cannula without using any force sensor. We will measure the deflection of the hybrid snake using theEM trackers and then will use the deformation model of the hybrid snake to calculate the tip force. Thecalculated force then will be sent to the haptic device. It is expected that the haptic feedback will increase theaccuracy of the physicians to perform blunt dissection with the snake. Sub-Aim #2.3: Path Planning: Coordinating all of the internal degrees of freedom of the robot is anambitious challenge, to say the least. Imagine trying to coordinate 102 knobs, one for each degree of freedomof the robot, to perform useful motion; it is impossible. Instead, the proposed work builds upon Choset’s
  • background in path planning to develop three modes of physician software support: 1) motion for thearticulated probe only, 2) motion for the steerable cannula, only, and 3) concurrent motion of the articulatedprobe and steerable cannula. Motion for the articulated probe is used for accessing the vicinity of the operativetarget; typically, the steerable cannula will be fully contained in the probe. Given a desired path, the first mode of planning is seemingly relatively straightforward because thearticulated probe is mechanically a follow-the-leader device, and was addressed in our previous work .However, the surgeon may select a path that is not optimal for a particular task. For example, the surgeon mayselect a path that places the mechanism in an awkward configuration from which other motions are notpossible or tip dexterity is compromised. To address this concern, we will develop a path optimizer thatmaximizes the manipulability of the mechanism along the path. Recall that manipulability is det( JJ T ) whereJ is the Jacobian of the forward kinematic map derived in the previous subaim. By maximizing this quantity,one can maximize the set of velocities at the tip a mechanism can achieve, i.e., maximize its manipulability.The proposed work will consider many forms of manipulability, such as manipulability integrated along thepath, manipulability integrated, yet weighted by arc length, along the path, etc. This type of optimization hasnot been done for articulated robots. Path planning for the steerable cannula: The significant contribution to path planning happens when weconsider simultaneous path planning for the articulated probe and the steerable cannula. The questionbecomes: which device should be moved to achieve a desired tip motion. Once again, we take recourse tonotions of manipulability to maximize the dexterity of the overall system. Let Jp and Js be the Jacobians of theprobe and steerable cannula, respectively. Now, form a new Jacobian by stacking these two matrices on top ofeach other. This meta-Jacobian can then be used in the manipulability calculation, resulting in a measure oftip dexterity for the hybrid snake. Now, one can specify an optimization problem that maximizes overallmanipulability to move the tip along desired directions. Such an optimization process will yield a planner thatoptimally moves the probe and cannula. This portion of the proposed work will investigate variations of thismeasure and validate this approach for planning. We should also stress that often the hybrid snake may be in contact with the environment, and it may benecessary to plan paths that regulate the force interaction between the mechanism and the anatomic target. To det ( J JT ) −1plan accordingly, we make use of force-manipulability which is . Extremizing this quantity allowsthe device to have a wide range of force control over the tip, but naturally at the loss of variations in velocity.This makes sense in that power, the product of force and velocity, must be conserved. The proposed work willconsider variations of these measure that combine manipulability and force-manipulabilty, say linearcombinations of the two. Such a planner has not been considered on highly articulated snake devices before,and potentially represents a significant contribution to the path planning literature. Finally, developments in path planning will assist the surgeon when performing the blunt dissectionprocess. Using the contributions to planning, described above, we will standardize the motion of the steerablecannula: into an up-and-down sweep followed by a right-to-left sweep, each repeated 3 times. This type ofmotion is called coverage (Choset, 2000, Acar, 2002), a type of planner that passes a robot end-effector overall points in a target region. Our research group lifted coverage into non-flat surfaces in three dimensions in(Atkar 2005); this work also considered optimizing a process variable, such a uniformity of paint in a surfacedeposition application. In the proposed work, we will build upon the prior coverage work to optimize deviationfrom a desired force profile while covering a non-flat surface, using the force path planners described above.With this planner in-hand, the surgeon can specify a region over which the two pairs of three paths should befollowed, and then will produce a path that covers the region while maintaining a desired force profile. Specific Aim #3: Develop 4D 3D image-guidance that shows the shape and position of the snake robotregistered to a patient-specific cardiac reconstruction. Sub-Aim #3.1: CT data collection and segmentation;Sub-Aim #3.2: Online reconstruction and SLAM; Sub-Aim #3.3: 34D rendered graphical interface. Sub-Aim #3.1: CT data collection and segmentation: Preoperative imaging is usually performed fordiagnostic purposes, but can also be useful for preoperative planning via the reconstruction of 3D surfacesfrom 2D image slices. These 3D reconstructions are also beneficial for live image-guidance when registered tointraoperative information such as real-time ultrasound or an electromagnetic tracker. 3D surfacereconstruction is obtained by segmenting the 2D image slices so as to associate each pixel with a specificorgan or internal structure. This process can be performed by thresholding the pixel values, by using themarching cubes algorithm , by manually segmenting portions of the images, or by implementing any
  • combination of the three aforementioned methods. We will use the open-source multi-platform 3D Slicersoftware package to perform 3D anatomical reconstruction from CT data. When we scan a subject using CT angiography, the output will be a set of DICOM files that are easilyimported into the 3D Slicer software package. From here, we will segment the images and create a 3Dreconstruction of the epicardial surface (as well as additional structures) using conventional segmentationtechniques. By implementing an extra C++ module, we will have Slicer output a custom data file that stores thesurfaces as separate triangle meshes that are compressed at different levels of detail and that are in a formatthat is easily parsed by our SLAM software as an initial reconstruction for initializing our 34D SLAM algorithm. In initial testing, we collected CT data for five patients. The CT data shows that the pericardialreflections can be seen by CT imaging. We will develop an additional C++ module for Slicer that will automatethe segmentation of the pericardial reflections. Sub-Aim #3.2: Online reconstruction and SLAM: A static 3D reconstruction from CT images is not arepresentative model of the operating site. We will use SLAM to estimate patient-specific motion parameters ofthe heart tissue in order to create a more informative 34D model. Our SLAM algorithm will also provideaccurate estimation of the relative pose of the snake robot, further enhancing the physician’s situationalawareness. This implies the need for accurate registration to the 34D reconstruction. Our SLAM method is initialized from the 3D static epicardial surface reconstruction from Sub-Aim 3.1. Wewill essentially use the static surface as a crude initial guess for the true 34D surface model. At first, this modelwill be incorrect, but through the SLAM algorithm’s filtering process, the motion parameters for each element ofthe surface triangle mesh will be incrementally adjusted when new intraoperative information is available. One type of measurement that will help determine motion of the heart tissue, and which will feed directlyinto the Kalman filtering framework that we will adopt for SLAM, is detected cyclical motion of the EM tracker atthe distal end of the snake robot. We will set the tip stiffness of the hybrid snake to a low value and navigatethe tip of the snake along the surface of the heart. The position data will provide a means to correct, online, thesurface parameters of the triangle mesh. We note that we will also navigate the hybrid snake through thepericardial reflections to further refine surface and motion information of this anatomical target. Another measurement that we will rely upon for estimating the motion parameters of our updated 34Dmodel will be visually tracked features from camera images that are recorded at the distal end of the snake.The measurements we obtain from this method are known in the robotics community to be “bearing-only”,which unfortunately requires unique attention for SLAM problems. Luckily, we already have in depthexperience performing a similar visual feature mapping task for SLAM [CITE]. While the SLAM filter itself will be based on Kalman filtering, a widely used estimation technique for linearproblems, we handle the nonlinearity inherent in the kinematic models for the hybrid robot by developing andthen implementing a novel iterative filtering technique to achieve better performance for motion estimation.This iterative method will be based on proven numerical optimization algorithms. Additionally, our SLAMalgorithm will use stochastic models, and thus, will maintain error bounds on the motion parameters that weare estimating for the heart surface. Lastly, the SLAM algorithm will automatically generate, via filtering and parameter estimation, the mostlikely pose of the robot. This means that the registration of the robot to the CT images will be updated andcorrected automatically during a surgical trial or an experiment. The initial guess for the registrationparameters, which will be used to initialize SLAM, will be based on the matching of 9 externally applied fiducialmarkers that are visible in the CT images. Sub-Aim #3.3: 34D Rendered Graphical Interface: For image-guidance, we propose an intuitive graphical interface that will display, on a computer screen, a34D rendered visualization of the operation which allow the physician to view the operating site from anyvantage point. This graphical interface will involve the incorporation of new software modules into the 3D Slicersoftware package [CITE]. The first step will be to implement a custom module that will render the snake robotamong the surface models of the heart. Both the surface models and the snake position estimate will be fedfrom an independently running software process that is performing the SLAM algorithm discussed in Sub-Aim3.2. Therefore, a second software module will be developed to load and parse SLAM data into Slicer from thissecondary process. The SLAM algorithm produces a 34D model, and thus it is important that we synchronize the animationtheupdate of the rendered epicardial surface with other the cardiac parameters, such as stiffness,motion of thesubject. This will be achieved by inputting a live ECG signal from the subject into the computer that is running
  • the graphical interface. The ECG will be used for timing purposes so that the appropriate model is rendered atthe correct instance in the cardiac cycle. One focus of this graphical interface will be to make the software as intuitive as possible for both surgeonsand engineers. This means that the inner workings and technical details of our SLAM algorithm will be hidden“under the hood”. Only the most likely rendered view of the operation will be displayed at any given time, whichwill simplify image-guidance for the user. If needed, the software will allow for easy switching between therendered visualization, direct vision, and/or a view of the CT DICOM files for planning. To show the directcamera feed, we will need to write additional C++ code that will also interface with Slicer and that will processthe image data. Implementing this intuitive interface will involve the development of C++ software for systemintegration. Potential Pitfalls and Solutions: There are several challenges associated with the development of thehybrid snake and its controllers. The first concern with the hybrid snake is the potential complexity due to thelength of its steerable cannula. As the length of the steerable cannula increases, the torsional twist of theconcentric tubes will increase and other potential phenomena may affect the kinematic mapping of thesteerable cannula. The second concern is the required strength for the articulated probe to bend the steerablecannula. To address these concerns, we will have the option of using multi-segment pre-curved tubes thateach segment has different material properties. We will consider using a material with low bending stiffnessand high torsional stiffness for portions of the tubes which are inside the articulated probe and use a materialwith a high bending stiffness for the portion which is outside of the articulated probe. We will also usefunctional approximation for building kinematics mapping that allows computationally expensive model to beimplemented. The third concern is the instability and oscillation that may cause due to the use of tip sensors in closedloop controllers. In order to prevent possible instability and oscillations, we will use aggressive analyticalmethods based on passivity theory and absolute stability theory to ensure the stability of hybrid snake in worstcase scenarios. Our team is uniquely qualified to address all of these issues. Finally, potential pitfalls may occur while running the SLAM algorithm for image guidance. If we happen tomiss-associate measurements from camera images with the wrong moving features in the 4D surfaceestimated by SLAM, then the estimated surface will have positional error. With robust visual feature trackingand conservative estimation, though, we believe this situation would be a rare occurrence.Also, if metal objects influence the accuracy of the EM tracker due to disruption to the generated magneticfield, both the snake robot and surface estimation within the SLAM filtering algorithm may be negativelyaffected. Any additional error like this will cause the 34D image-guidance rendering to be a misrepresentationof the operating site, which is cause for concern. In our preliminary work, though, we have thoroughly testedthe EM tracker inside and outside of a surgical environment and are confident in its accuracy when integratedwithin the HARP robot. SPECIFIC EXPERIMENTAL PROTOCOLS: We will use our well established porcine preparation for allanimal experiments, starting in Year 2 (see Table X). Large (35-45kg) healthy swine of either sex will bereceived by the Harvard Medical School Animal Research Facility (West Roxbury VABHCS Campus) andhoused at least overnight following delivery. On the first experimental day, subjects will receive intramuscular injections of 20 mg/kg ketamine and2 mg/kg xylazine and 1% to 5% isoflurane will be delivered using a face mask for general endotrachealanesthesia (GETA). Nine metal fiducial markers will be placed on the skin of the ventral thorax and computedtomography (CT) will be performed. 3D CT images will be obtained using an helical CT scanner (64-sliceLightSpeed VCT; GE Healthcare, Milwaukee, WI). CT scanning (120kV, 800mA, pitch of 0.16:1,350ms/rotation gantry speed) with a thickness of 0.6mm after intravenous injection of an iopamidol contrastagent. Following the procedure, subjects will be extubated and observed in the recovery room. The CT DICOMfile will be obtained from the Radiology Department and volume rendering with SLICER or other software willbe performed. On the second experimental day, subjects will receive GETA and will be placed supine on theoperating table. Heart rate and rhythm will be monitored continuously with electrocardiography. The rightcarotid artery and jugular vein will be exposed through an incision on the right side of the neck and the rightcarotid artery will be cannulated with a 6 French catheter to monitor the arterial blood pressure. The jugularvein will be cannulated with a 7 French Swan-Ganz catheter to monitor the central venous pressure, the
  • pulmonary artery pressure and mixed venous oxygen saturation derived from blood samples obtained from thetip of the Swan-Ganz catheter placed in the pulmonary artery. The AURORA tracking system (NDI, Waterloo, Canada) will be mounted on the operating table. Theworking tip of the hybrid snake is tracked with respect to these fiducials using an embedded three-axismagnetic tracking coil. A user interface will graphically represent the heart and surrounding mediastinalstructures. The hybrid snake will be introduced inside the pericardial cavity through a single 15mm Subxiphoid portas previously described .The HARP will be advanced using both direct endoscopic visual feedback and imageguidance with the display interface. Once the HARP reaches the target reflection, it will be locked into placeand the steerable cannula will be introduced and advanced (MM: alternative is having the HYBRID SNAKEalready assembled). Additional imaging will be acquired with an 8FR AcuNav intracardiac ultrasound probe(ICE, Acuson Inc) in order to identify the RIPV and IVC and measure the distance. Blunt dissection of thetarget pericardial reflection will be obtained by repeating a gentle alternating sweeping motion of the steerablecannula according to a plan taking into consideration the dexterity of the hybrid snake at the target location andthe intravascular and intracardiac pressure measured with ICE. The path planning technology, described inAim 2.3, will reduce the cognitive load on the surgeon to achieve blunt dissection: instead of directly controllingmany degrees of freedom, the surgeon specifies a region in an image of the operating site, and then theplanner automatically the steerable cannula in an up-and-down sweep, repeated 3 times, followed by a right-to-left sweep, also repeated 3 times. The range of the sweep will be predetermined based on the combinedICE and CT measurement (e.g. distance from the cranial edge of the inferior vena cava to the caudal edge ofthe right inferior pulmonary vein for target #1). Successful dissection of reflection #1 will be defined by the ability of the entire hybrid snake to advancethrough the dissected path. For reflections #2, 3 and 4, success will be defined as the advancement of the tipof the steerable cannula past the anatomical boundaries of the reflection. Safety will be monitored by absenceof blood in the pericardial cavity under direct video monitoring, lack of hemodynamic changes and arrhythmias.Following the completion of all 4 blunt dissections, a sternotomy will be peformed and each dissection will betested with the Wolf Lumitip Dissector (Atricure, West Chester, OH). For each blunt dissection, we will record the following parameters: (a) time from first steerable cannuladissection to confirmation of successful completion of task; (b) extent of deformation of surrounding vascular orcardiac structures (in mm) by ICE; (c) subjective level of difficulty by the operator on a scale of 1 (very difficult)to 5 (very easy); (d) presence or absence of complications. Following complete dissection of the 4 pericardial reflections, a commercially available RF ablationcatheter (ThermoCool, Biosense-Webster) will be advanced through a working port and, using a combinationof imaging including direct video endoscopy and ICE, the catheter will be used to perform the epicardial fivebox Maze. The steerable cannula of the hybrid snake will be used to facilitate access of the RF catheter byproviding retraction of atrial tissue. Bidirectional (i.e. entry and exit) block will be confirmed for each one of thefive boxes, and additional ablation will be used until complete block is confirmed. We propose to compare the HARP to the hybrid snake for the ability to a) complete the dissection of the 4pericardial reflection targets and (b) perform the five box Maze. Data Analysis: Quantitative results will be expressed as the mean percent change from each subjectbaseline of a given parameter ± the standard error of the mean (SEM) and analyzed using a software packagefor statistical analysis (Stata/IC software, version 10.1; Stata Corporation, College Station, TX). Thesepercentage changes will be compared between groups. Wilcoxon’s signed-rank test will be used to determinethe significance of the difference. P value of less than 0.05 will be considered statistically significant.Arrhythmogenicity will be reported qualitatively in a binary manner as either the presence or absence ofoperator-identifiable arrhythmia on EKG. Work Plan: The work plan spans five years, and the specific aims and tasks will be completed as shownin the table and chart the below.
  • YEAR Harvard Medical School Carnegie Mellon University Year 1 Design 1 of steerable cannula (Aim 1) Feeder design (Aim 1) CT data and collection (Aim 3) Kinematic model & position control (Aim2) Year 2 Test snake in phantom (Aim1-2) Design a strong probe (Aim 1) Design 2 of steerable cannula & control (Aim 1-2) Construct new feeder (Aim1) Path planning (isolated mechanisms) (Aim 2) Online reconstruction and SLAM (Aim 3) Preliminary animal test (N=5) Year 3 Stiffness control of snake [Aim 2] Continue on design of the probe (Aim1) Animal testing for pericardial dissection (N=10) Path planning (combined mechanism) (Aim2) 34D rendered and SLAM (Aim 3) Year 4 User interface design for snake [Aim 3] Iterate on feeder design (Aim 1) Imaging & segmentation[Aim 3] Path planning using results from SLAM (Aim2) Animal testing (N=15) [Aim 1-3] 34D Rendering graphical interface (Aim 3) Year 5 Imaging & segmentation [Aim 3] Fully integrate interface, planning and SLAM Snake vs HARP for dissection (N=20) (Aim 2 and 3) Five Box Ablation in human cadavers (N=5) Investigators Choset has been leading a research group for over 15 years developing a comprehensive program onsnake robots. These work touches about key areas: mechanism design, path planning, control, and estimation.Choset’s research group has developed the most varied collection of snake robots in the nation, and thesedevices have been patented, as well as deployed for real use. Choset goes beyond building the device toenabling it to perform purposeful motion. Choset has received many awards, such as the NSF Career Awardand ONR Young investigator award, for his work on path planning; five years ago, he published a book pathplanning with the MIT Press where Choset is the first author. Choset’s students have won many best paperand video awards on their work on control, most recently best video for a climbing robot at the InternationalConference on Robotics and Automation. Finally, Choset’s group has developed estimators to localize mobilerobots in large spaces. Few researchers in robotics work on all four of these topics and no other group canintegrate them.
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