Surgery with cooperative robots

Abstract

Advances in endoscopic techniques for abdominal procedures continue to reduce the invasiveness of surgery. Gaining access to the peritoneal cavity through small incisions prompted the first significant shift in general surgery. The complete elimination of external incisions through natural orifice access is potentially the next step in reducing patient trauma. While minimally invasive techniques offer significant patient advantages, the procedures are surgically challenging. Robotic surgical systems are being developed that address the visualization and manipulation limitations, but many of these systems remain constrained by the entry incisions. Alternatively, miniature in vivo robots are being developed that are completely inserted into the peritoneal cavity for laparoscopic and natural orifice procedures. These robots can provide vision and task assistance without the constraints of the entry incision, and can reduce the number of incisions required for laparoscopic procedures. In this study, a series of minimally invasive animal-model surgeries were performed using multiple miniature in vivo robots in cooperation with existing laparoscopy and endoscopy tools as well as the da Vinci® Surgical System. These procedures demonstrate that miniature in vivo robots can address the visualization constraints of minimally invasive surgery by providing video feedback and task assistance from arbitrary orientations within the peritoneal cavity.

• Cooperative
• robots
• laparoscopy
• translumenal
• natural orifice

Introduction

Surgical procedures performed through small incisions reduce patient trauma, leading to shortened recovery times and improved cosmesis as compared to open procedures. While laparoscopy reduces invasiveness by creating small incisions in the abdominal wall, Natural Orifice Translumenal Endoscopic Surgery (NOTES) completely eliminates external incisions by gaining access to the peritoneal cavity through a natural orifice.

Each of these approaches to minimally invasive surgery limits the surgeon's ability to visualize and dexterously manipulate the surgical target. The long rigid tools inserted into the peritoneal cavity through small incisions for laparoscopic surgery limit the surgeon's range of motion, and therefore the complexity of the procedures that can be performed. Similarly, NOTES procedures are surgically challenging. The tools must be completely flexible to traverse the natural lumen, and the use of multiple tools is limited by the size of the natural orifice.

Telerobotic systems for the manipulation of laparoscopic tools or cameras, such as the da Vinci® Surgical System (Intuitive Surgical, Sunnyvale, CA, http://www.intuitivesurgical.com), have been developed to address the limitations of laparoscopic surgery. These systems enhance surgical dexterity through stereoscopic vision, dexterous end-effectors, and tremor filtering, but remain constrained by the entrance incision. An alternative approach to addressing the constraints of laparoscopic and NOTES procedures is the use of miniature in vivo robots that can be completely inserted into the peritoneal cavity through a standard trocar or a natural orifice. Such robots can provide the surgeon with vision and task assistance without being constrained by the entry incision.

This paper demonstrates the feasibility of using multiple miniature in vivo robots in cooperation with existing tools and telerobotic systems to mitigate the constraints of traditional minimally invasive procedures. Three non-survival porcine model surgeries are presented, including a cooperative da Vinci® cholecystectomy, a multiple miniature robot laparoscopy, and a cooperative NOTES procedure.

Laparoscopic surgery

Laparoscopy reduces patient trauma, but is inherently limited in scope and complexity compared to open surgery where the surgeon can directly view and touch the surgical environment. The surgeon's ability to visualize and dexterously manipulate the surgical target is limited by working with long, rigid tools inserted through access ports in the abdominal wall. These ports constrain the motion of the tools and camera to arcs of a sphere centered on the insertion point. Furthermore, a two-dimensional (2D) image limits the overall understanding of the surgical environment [1], [2] and the field of view provided to the surgeon cannot encompass the frequent tool changes, potentially leading to accidental injury to organs and vascular structures [3], [4].

These limitations have contributed to slowing the expansion of laparoscopic techniques to complex procedures. The rapid development of minimally invasive surgery as an alternative to conventional surgery, beginning in the 1990s [5], prompted a paradigm shift in surgical methods [6], [7]. Laparoscopy is now the preferred intervention for many routinely performed interventions such as gallbladder excisions: in 1999, 85% of all gallbladder removals in the US were performed laparoscopically [8]. However, the widespread application of minimally invasive surgery to other, more complicated procedures has remained limited. For example, in 2000, less than 3% of colon resections [9] and only 17% of cardiothoracic surgeries [8] were performed laparoscopically.

Natural Orifice Translumenal Endoscopic Surgery (NOTES)

The invasiveness of surgical procedures can be further minimized by gaining access to the surgical site through a natural orifice. The feasibility of NOTES has been demonstrated in several survival transgastric studies in animal models, including peritoneal exploration [10], fallopian tube ligation [11], organ resection [12], gastrojejunostomy [13], partial hysterectomy [14], gastrojejunal anastomosis [15], lymphadenectomy [16], and oophorectomy and tubectomy [17]. Alternative approaches to the peritoneal cavity, including transvesical and transcolonic approaches, have also been demonstrated [18], [19], [20].

The NOTES approach is currently being evaluated in human studies. The first transvaginal-assisted cholecystectomy in the US was performed by Marc Bessler (New York Presbyterian Hospital/Columbia University Medical Center) in March 2007 [21]. Subsequently, a series of natural orifice surgeries using the transgastric approach were performed by Lee Swanstrom (Oregon Clinic) using the EndoSurgical Operating System™ (USGI Medical, Inc., San Clemente, CA) [22].

Instruments for NOTES

While the above studies have demonstrated that a NOTES approach is feasible, they have also determined that conventional endoscopy tools impose significant constraints. For example, it is difficult to work with a limited 2D image of the surgical environment when the exact orientation of the long, flexible scope is not intuitively obvious to the surgeon [23]. Furthermore, the lack of triangulation between the imager and the tools restricts the surgeon's ability to judge depth, and thereby limits his dexterity [24], [25]. The use of two independent flexible endoscopes with separate displays to improve visualization also met with limited success, again because both scopes entered through the same orifice and did not provide adequate triangulation with the tools [25].

Clearly there is a need for new instruments for NOTES that improve the surgeon's ability to visualize and manipulate the surgical target within the peritoneal cavity. Technology, including robotics, has significantly influenced laparoscopic surgery and has the potential to revolutionize NOTES by mitigating the visualization and dexterity constraints.

Robotic surgical assistants for minimally invasive surgery

The application of robotics to enhance the surgeon's ability to visualize and dexterously manipulate the surgical target is recognized as having a significant impact on the advancement of minimally invasive surgery [26–28]. The first robotic device to receive Food and Drug Administration approval for direct surgical manipulation in laparoscopy was the Automated Endoscopic System for Optimal Positioning (AESOP) [26]. AESOP was introduced in the mid 1990s for the control of a laparoscopic camera during surgical procedures. More advanced tele-robotic devices, including Zeus and da Vinci®, allow the surgeon to control the robotic arms holding the surgical instruments while located at a remote surgical workstation. The advantages of such systems include tremor reduction, improved distal tip dexterity, corrections for motion reversal, and motion scaling.

The da Vinci® system is the only commercially available surgical robot for performing complex abdominal and chest procedures. In this system, a stereoscopic image of the surgical environment is displayed at the hands of the surgeon, creating the illusion that the surgical tools are extensions of the surgeon's hands [26]. The da Vinci® system's stereoscopic visual feedback of the surgical field has been shown to reduce the incidence of skill-based errors as compared to traditional laparoscopic surgery [29]. However, the application of the da Vinci® system has remained limited, with many of the dexterity and visualization benefits being realized only for more complex laparoscopic procedures.

Much effort is being directed towards the development of next-generation robots with improved mobility and sensing and reduced complexity and cost. For example, some research focused on the development of a master-slave telerobotic system with enhanced dexterity and sensing using millimeter-scale robotic manipulators [30]. Intelligent microsurgical instruments are also being developed for filtering involuntary hand motion in handheld instruments A full prototype of this device has demonstrated a reduction in tremor oscillations by as much as 50% [31], [32]. Other work focused on developing smaller telerobotic surgical systems with improved haptics [33], [34].

Although many of the robotic developments for minimally invasive surgery have focused on mitigating the limitations of working through a small incision, these devices will always be constrained to some degree by the fulcrum effect.

In vivo surgical robots for minimally invasive surgery

A fundamentally different approach to externally implemented robotic systems for minimally invasive surgery is the use of robotic devices where all or most of the device enters the body. Many of these applications are based on the flexible endoscopy platform. The complexity of these devices ranges from endoscopes with distal tip maneuverability for flexible endoscopy [http://www.olympusamerica.com, 35] and laparoscopy [36] to more advanced devices with locomotion systems for exploration of hollow cavities including the colon and esophagus [37–39].

Completely passive capsules, including PillCam® and EndoCapsule®, that are swallowed and return images as they pass through the gastrointestinal tract, are currently being marketed [40], [41]. However, the exact locations of the images returned by a passive capsule are not known, and the surgeon cannot direct the device to a specific location to investigate or administer therapy. Meanwhile, an endoscopic minirobotic legged capsule is being developed that introduces a locomotion system into a platform similar to the passive capsule, thereby enabling the active exploration of the entire gastrointestinal tract [42]. Still another device, the HeartLander, is being developed to traverse and deliver therapy to the surface of a beating heart [43].

The work within our research group focuses on the development of miniature in vivo robots to assist in laparoscopic procedures. Our preliminary work strongly suggests that miniature robots that are inserted completely into the peritoneal cavity can overcome some of the limitations of current surgical robotic systems by restoring lost degrees of freedom. The miniature in vivo robots developed can be classified as having either a fixed-base or mobile platform.

Laparoscopic robots with a fixed-base platform are primarily used for providing auxiliary visual feedback to the surgeon, giving an enhanced field of view from arbitrary orientations. These robots are initially positioned by the surgeon, and can be reoriented as needed throughout a procedure without necessitating additional incisions. Initial work included the development of a 15-mm diameter pan-and-tilt camera robot with LEDs and a tripod platform [44], [45]. This robot was used with a laparoscope to perform a non-survival cholecystectomy in a porcine model.

Mobile robots provide vision and task assistance from a remotely controlled wheeled platform. A helical wheel design has enabled these robots to maneuver on all of the pelvic organs and to climb deformable structures up to three times their height without causing any visible tissue damage [46]. A mobile robot with an adjustable-focus camera has provided the sole visual feedback for a laparoscopic cholecystectomy in a non-survival porcine model [47], and a similar robot with the addition of a biopsy forceps device has demonstrated the feasibility of performing a single-port laparoscopic biopsy [48]. In additional testing, the in vivo mobile robot design was used during a non-survival NOTES procedure in a porcine model [49].

Robot designs

Multiple miniature in vivo robots have been developed to assist cooperatively in laparoscopic and NOTES procedures, as well as to assist the da Vinci® Surgical System in performing complex laparoscopic procedures.

Peritoneum-mounted imaging robot design

The primary parameters considered in the design of the imaging robot, shown in Figure 1, were providing a stable, repositionable platform for visualization while allowing unobstructed access to the surgical site for da Vinci®.

Figure 1. Overview of first-generation peritoneum-mounted imaging robot system. [Color version available online.]

Attachment method

Significant consideration was given to the method of attachment for the imaging robot. Several mechanisms for attaching the robot to the interior abdominal wall were considered. Many of these used various configurations of needles and hooks for physical attachment to the abdominal wall. An additional design used two sets of magnets, one set placed at each end of the robot and a second set housed in a magnet handle located on the exterior abdominal wall. The attraction of these magnet pairs was used to attach the robot to the abdominal wall.

In vivo testing of the fabricated mechanisms identified significant constraints when using the needle and hook attachment mechanisms. Accurate positioning of these devices was difficult – and sometimes impossible – using standard laparoscopic tools. Significant oscillations of the robot were observed with small inputs from inside or outside the abdomen. In contrast, the magnetic attachment mechanism proved a simple way to attach and position the robot. This method provided a more stable platform than the needle and hook attachment mechanisms because of the larger contact area with the abdominal wall.

Robot design

To meet the needs of the cooperative surgical environment, the imaging robot was designed with sufficient functionality, including panning and tilting capabilities, to provide useful video feedback of the surgical target. The basic design consists of a stationary outer tube with a rotating inner tube that houses the lens, camera board, and three permanent magnet direct current (DC) micromotors. A schematic of the design is shown in Figure 2. A tilting front-surface mirror is used to minimize the overall robot diameter and complexity by allowing for a stationary camera and lens.

Figure 2. Solid model of first-generation peritoneum-mounted imaging robot showing configuration of major components. [Color version available online.]

Panning of the camera about the robot's axis is accomplished by rotating a planet gear about a stationary sun gear fixed to the outer tube. The camera can be panned up to 45° in either direction. Tilting of the image is accomplished by tilting the front-surface mirror. A motor fitted with a lead screw is used to move a lead nut in a guide slot along the length of the inner tube. A pin attached to the lead nut slides in a second guide slot in the mirror mount, tilting the mirror to different angles as the lead nut traverses along the lead screw. A motor fitted with a lead screw and lead nut with attached lens is used for focusing the camera. As the motor rotates, the lead nut moves in a guide slot along the length of the robot. This mechanism is optimized for focusing on objects located at distances between 50 and 200 mm from the robot. Each end of the outer tube is capped with a magnet holder.

Next-generation peritoneum-mounted imaging robot design

The next-generation peritoneum-mounted imaging robot, shown in Figure 3, maintains the same basic functionality as the previous-generation imaging robot, but with a reduced diameter of 12 mm and the addition of LED lighting. This robot is designed to be inserted into the insufflated abdominal cavity using a standard trocar during laparoscopy or using the upper approach in NOTES. A single permanent magnet DC micromotor is used to remotely tilt the camera to arbitrary angles. The adjustable-focus video feedback from the imaging robot is viewed by the surgeon on a standard monitor. The on-board lighting enables this device to provide video feedback to the surgeon independent of an additional light source.

Figure 3. Overview of next-generation peritoneum-mounted imaging robot system. [Color version available online.]

A magnetic handle on the outside of the patient is used to hold the camera to the peritoneum. Similar to the previous-generation robot, the handle contains magnets that attract magnets embedded in the robot. The handle can be moved across the exterior of the abdomen, effectively positioning and panning the robot.

Mobile camera robot design

The general design for a mobile in vivo robot, shown in Figure 4, consists of two wheels with a very specific tread design allowing the robot to traverse within the abdominal cavity. The independently driven wheels enable forward, reverse, and turning motions. A tail that collapses into the wheel tread for insertion through the trocar is used to prevent counter-rotation. A 6-mm diameter permanent magnet DC micromotor is attached to each wheel using bearings and spur gears.

Figure 4. Mobile camera robot design. [Color version available online.]

The robot also carries an adjustable-focus image sensor to provide real-time video feedback to the surgeon. As discussed previously, the viewing capabilities of mobile camera robots and the feasibility of using them during minimally invasive surgery has been demonstrated in several non-survival porcine procedures.

Lighting robot design

The lighting robot, shown in Figure 5, uses the same outer tube and end cap as the next-generation imaging robot discussed previously. The clear outer tube houses six white LEDs. Each endcap contains magnets that are used with an external magnetic handle to attach the lighting robot to the interior abdominal wall. As with the imaging robot, this lighting robot can be inserted through a standard trocar during laparoscopic surgery. This robot can also be advanced through the mouth and esophagus and inserted into the peritoneal cavity through a transgastric incision.

Figure 5. Lighting and retraction robots for minimally invasive surgery. [Color version available online.]

Retraction robot design

The retraction robot is also designed to be placed entirely into the peritoneal cavity through a standard trocar or natural orifice. Once inside the peritoneal cavity, the robot provides a stable platform for gross tissue retraction during a surgical procedure. The basic design of the robot consists of a body with two embedded magnets and a tethered grasping device, as shown in Figure 5. An 8-mm permanent magnet DC micromotor housed in the body of the robot is coupled to a drum. As the motor rotates, a tether is wound or unwound about the drum depending on the direction of rotation. Laparoscopic or endoscopic tools are used to actuate the grasping device. In the near future, a cooperative robot will assist with this task.

Results

Cooperative laparoscopic procedure using da Vinci® and an in vivo robot

The first-generation peritoneum-mounted imaging robot was successfully used cooperatively with the da Vinci® Surgical System to perform a non-survival cholecystectomy in a porcine model. The robot provided the primary non-stereo visual feedback to the da Vinci® console, with the video feedback from the da Vinci® laparoscope being primarily used for initial positioning of the imaging robot and as a light source, as shown in Figure 6. The robot was positioned and actuated throughout the procedure to optimize the feedback available to the surgeon.

Figure 6. Cooperative laparoscopic da Vinci® procedure as viewed from da Vinci® laparoscope (left) and imaging robot (right). [Color version available online.]

The da Vinci® system was positioned above the porcine model as per normal procedure. Three small incisions were made in the abdominal wall for two tool ports and a laparoscope. A special, slightly larger trocar was used for the insertion of the in vivo robot. The remaining trocars were then placed and the abdomen insufflated. The da Vinci® tools and laparoscope were then inserted and readied for the procedure.

The in vivo robot was lifted from the organs by positioning the external magnetic handle over the robot location in the abdomen and pressing the handle down toward the robot. When the handle magnets were sufficiently close to the magnets embedded in the robot, the robot was lifted to the upper abdominal wall. The robot and tools were positioned using the robot camera and the da Vinci® laparoscope. Robot functions were checked to confirm proper operation, and the light intensity was adjusted to provide the best image from the robot.

The operating surgeon then began performing the cholecystectomy. The robot was repositioned and actuated to track tool movements throughout the procedure. To accomplish this, the robot operator relied on visual cues on the surgical monitor and voice commands from the surgeon. The lens position was also adjusted throughout the procedure to focus on the da Vinci® tools. The laparoscopic cholecystectomy was performed per normal procedure using the da Vinci® system tools, but with primary video feedback coming from the imaging robot. After the cholecystectomy, the robot was moved back to the special trocar, the abdomen deflated, and the robot retracted by its tether.

The multiple viewpoints available through the use of the cooperative robot improved the surgeon's understanding of the surgical environment. Video quality was a concern for this initial robot, but proved adequate for performing the surgery. Higher quality optics are needed to increase image quality. Overall, the cooperative da Vinci® procedure was a success as the robot operated without error for the entire procedure.

Cooperative laparoscopic procedure using two in vivo robots

A cooperative in vivo robot laparoscopic procedure was performed in a non-survival porcine model using a next-generation peritoneum-mounted imaging robot and a mobile camera robot. Three abdominal incisions were made in an anesthetized pig. A standard trocar was inserted through one of the incisions and was used for the insertion of the mobile camera robot into the peritoneal cavity. The abdominal cavity was then insufflated. The laparoscope was advanced through this same port to provide initial lighting for the mobile camera robot. The video feedback from the mobile camera robot was used by the surgeon to help plan the placement of two additional trocars and to view the trocar insertions. The imaging robot was then inserted through the same trocar as the mobile camera robot and was secured to the interior abdominal wall using the external magnetic handle. The imaging robot and mobile camera robot, shown in Figure 7, provided the surgeon with the primary video feedback throughout the procedure. Lighting was provided by the imaging robot.

Figure 7. Imaging (a) and mobile camera (b) robots provide video feedback (c and d) during the cooperative laparoscopic procedure. [Color version available online.]

Using the video feedback from the mobile camera robot and the imaging robot, the surgeon explored the entire peritoneal cavity. The wheeled mobility of the mobile camera robot enabled the surgeon to view the surgical environment from a low perspective, with the adjustable-focus camera allowing the surgeon to focus on areas of specific interest. The surgeon was able to maneuver the mobile camera robot throughout the entire peritoneal cavity, including over the bowel and liver. The view from the imaging robot provided the surgeon with an overhead view of the surgical environment. By changing the position of the external magnetic handle, the surgeon was able to reposition the imaging robot internally. This enabled the surgeon to explore the entire peritoneal cavity from multiple perspectives without the need for additional incisions.

The surgeon used the video feedback from the imaging robot to identify the surgical target for small bowel manipulation. The mobile camera robot was then driven to the surgical target to provide an additional view of the target from a lower perspective. Using only the video feedback from the two miniature in vivo robots, the surgeon performed the small bowel manipulation and suturing.

The video feedback from multiple, easily repositionable perspectives enhanced the surgeon's ability to perform laparoscopic suturing. Furthermore, both in vivo robots were fully inserted into the peritoneal cavity through the first trocar, allowing the surgeon to use this same trocar for the insertion of a third tool during small bowel suturing. The reduction in the number of incisions required for performing a surgical procedure will further improve patient recovery and cosmesis.

Cooperative NOTES procedure using three in vivo robots

The next-generation imaging robot, lighting robot, and retraction robot were used in cooperation with a standard upper endoscope to demonstrate various capabilities in a non-survival NOTES procedure in a porcine model. Prior to insertion of the robots, the endoscope was used to advance an overtube into the peritoneal cavity. Using the endoscope, the imaging robot was advanced through the overtube and into the peritoneal cavity. Once each robot was inserted, it was independently attached and positioned along the upper abdominal wall, as shown in Figure 8, using external magnetic handles. The surgeon used the external magnetic handles to reposition the robots throughout the procedure.

Figure 8. Imaging, lighting, and retraction robots as viewed by endoscope during cooperative NOTES procedure. [Color version available online.]

The surgeon used the video feedback from the imaging robot to explore the peritoneal cavity and to manipulate the bowel and gallbladder. The gross tissue manipulation capabilities of the retraction robot, also shown in Figure 8, were used to provide improved endoscopic access to the surgical target.

This procedure further demonstrates the feasibility of using multiple miniature in vivo robots in conjunction with traditional minimally invasive surgical tools to perform surgical procedures. The stable image and additional lighting were crucial to the surgeon's ability to explore and manipulate tissue within the peritoneal cavity using a NOTES approach.

Discussion

These cooperative in vivo robot procedures successfully demonstrate the feasibility of providing the surgeon with multiple, adjustable views of the surgical environment for minimally invasive procedures in the peritoneal cavity. Miniature in vivo robots can assist in the performance of complex da Vinci®-based procedures by providing visualization that improves the understanding of the surgical environment and assists in the prevention of off-camera arm collisions. The design of the imaging and mobile camera robots used in the cooperative laparoscopic procedure allowed for insertion through a single standard trocar, thereby reducing the number of abdominal incisions, while providing the surgeon with multiple views from differing perspectives. The use of cooperative in vivo robots for NOTES addresses significant constraints of existing methods for performing these procedures. The video feedback provided by the imaging robot provided an intuitive understanding of the surgical environment, and the retraction robot enabled off-axis gross tissue manipulation.

The ability to use multiple robots to cooperate with existing endoscopy tools and the da Vinci® system demonstrates the potential for a family of miniature in vivo robots to improve surgical care for routine and complex abdominal procedures. Future developments will enable the in vivo robots to provide additional task assistance, including grasping and cautery, for laparoscopic and NOTES procedures.