We have tested our robotic endonasal skull base system using various tasks and anatom- ical models. In the sections that follow, we detail experiments that were designed to test the usability and dexterity of our system, the utility of our system, and the feasibility of our system.
5.5.1 Pick and Place Task
The aim of this demonstration experiment was to test the ease of use and dexterity of the system by performing a standard laparoscopic task from the Fundamentals of Laparoscopic
Surgery Skill assessment and training program [191]. The goal was to pick up objects from one location and transfer them to another location using the gripper end-effector attached to the end of a concentric tube robot. The experimental setup used for this study is shown in Fig. 5.11. A peg board (100×64 mm) was rigidly attached in front of the robot and the pegs were arranged in a hexagon pattern on the left side of the board (horizontal distance 35 mm and vertical distance 17.3 mm between pegs) and in a rectangular pattern on the right side of the board (horizontal distance 30 mm and vertical distance 17.3 mm between pegs).
Teleoperative control of the robot was implemented as described in [107], such that the robot is able to move in a manner that, from the surgeons perspective, is similar to the da Vinci interface of Intuitive Surgical, Inc. (Sunnyvale, USA). In our system, the surgeon manipulates a user interface (Phantom Omni, Sensable, USA) that controls the position and orientation of the robot manipulator. The surgeon presses a button on the interface to
“clutch in” and begin controlling the tip of the manipulator. The surgeon can “clutch out”
by releasing the button to reposition his or her hands to a more comfortable position without moving the robot. Using software, we implemented motion scaling to scale down the ratio between the input device velocities and the tip velocities of the end effector, reducing the effects of hand tremor and enabling the surgeon to make more precise movements.
Prior to the experiment, users were given some time to maneuver the robot and establish their preferred motion scaling ratio. The user was then told to transfer the rings from the right side of the board to the left in whatever order he or she preferred. The performance metrics recorded were the number of successful ring transfers, the time taken, and the number of rings dropped. The experiment included a total of 10 participants, some of whom were expert users, others were novices, and two surgeons with moderate familiarity with the system. The results of the experiment are shown in Table 5.2. The mean task completion time of this experiment was 232.4 s with a standard deviation of 33.7 s over all trials, with only one novice user dropping any rings. It is interesting to note that the
Figure 5.11: The experimental setup used for the pick and place task is shown. The goal was to transfer the six rings from the right side of the peg board to the left side as quickly as possible without dropping any rings.
Table 5.2: Results for transfer task user study.
User Time (s) Drops
1 187 0
Novice 2 275 2
3 237 0
4 241 0
5 261 0
Expert 6 206 0
7 270 0
8 244 0
Surgeon 9 220 0
10 183 0
novice group performed the task slightly faster on average than the expert group, although the difference is not statistically significant. This may indicate that the learning curve of the system is not steep.
5.5.2 Phantom Tumor Removal
We also tested our robotic endonasal skull base system by performing a phantom tumor removal. We constructed the phantom tumor material using SIM-TEST (Corbin, USA) mixed with water in a ratio of 1 part SIM-TEST to 5 parts water as was done in [148], where the phantom was shown to resemble a pituitary tumor in terms of consistency and required
Figure 5.12: Experimental setup for phantom tumor resection experiments using the Phantom Omni user interface.
resection force. The phantom tumor was placed in the skull base of an anatomical skull model (# A20, American 3B Scientific, USA) that the surgeon prepared to closely replicate an enlarged sella as commonly found in pituitary tumor patients. The longitudinal axis of the prepared sella had a length of 3.18 cm, the vertical axis had a length of 2.11 cm, and the lateral axis had a length of 1.97 cm. The total volume of the sella cavity was 6.92 cm3. The surgeon navigated the robot using a Phantom Omni input device through the nasal passage and was tasked with removing as much of the phantom tumor as possible, using only a standard straight rigid 4 mm endoscope with a view angle of 30◦for visualization.
Both the endoscope and the skull were fixed in place during the procedure (see Fig 5.12 for experimental setup). Manual suction was used to clean the curette from time to time but not to remove phantom tissue directly from within the sella.
The experienced skull base surgeon performed 20 removals of the phantom pituitary tu- mor using the robotic endonasal system. The percent removal for each trial was determined using the weight of the skull before and after the experiment. We also recorded the total time for each removal. Fig. 5.13 shows the percentage removal and time for each removal.
The average percentage removal was 79.8 ± 5.9% and the average time to complete the
Figure 5.13: Percentage removal and time to complete removal are shown for all 20 removals using the Phantom Omni. The average percentage removal and average time for removal are overlaid on the data, and the trials are listed in order of completion.
removal was 12.5 ±4.1 minutes, which is comparable to current removal percentage and procedure times (see Sec. 5.7 for additional details regarding clinical removal percentage and procedure time). A thin film of the phantom tumor that covered the surface of the sella was all that was typically left behind after each trial.
5.5.3 Wrist Integration with Endonasal System
One of the most useful features of the dexterous wrist presented in Chapter 3 is the ease with which it can be integrated into needle-sized tools and devices. In order to illustrate this principle, we integrate the wrist with the endonasal concentric tube robot system (see Fig. 5.14(a)) and validate the use of the wrist in this procedure by removing gelatin from a phantom skull base model using the same experimental setup described in [107]. An endoscope view of the wrist deflecting to deliver the phantom tumor to the suction device is shown in Fig. 5.14(b). This qualitative analysis illustrates the utility of the dexterous wrist for skull base applications.
(a) (b)
Suction
Figure 5.14: (a) Photograph of our wrist integrated directly into the inner-most tube of the concentric tube robot, with an inset showing a closer view of the wrist and surgical curette attached to the wrist.
The diameter of the wrist is 1.16 mm. (b) Here, an endoscope view shows the concentric tube robot with integrated wrist being used to remove a gelatin tumor from a skull base phantom model.
5.5.4 Cadaver Workspace Study
To determine clinical feasibility we evaluated our system in a cadaver study. The nasal passages were surgically prepared, the sphenoid sinus exposed, and the anterior wall of the pituitary gland opened. The head was situated on the operating table in the typical position used in endonasal surgery. The robot was situated on the operating table at a rel- ative angle of approximately 45◦to the head (see Fig. 5.15(a) for the experimental setup).
A straight rigid endoscope with 4 mm diameter and a view angle of 30◦ was manually
Figure 5.15: Proof of concept cadaver study. (a) System setup in cadaver head study. (b) The two concentric tube robots enter through one nostril. (c) Sagittal view onto surgical site. The endoscope and the two robot arms are shown approaching the frontal wall of the pituitary gland. (d) Intraoperative endoscope view onto the pituitary gland in cadaveric study.
inserted through the nostril and manually maintained in position. Both robotic arms were inserted through the right nostril (see Fig. 5.15(b)) and could reach the pituitary gland while maintaining maneuverability. Fig. 5.15(c) shows an intraoperative image of the endoscopic view onto the pituitary gland. In order to fully observe the instrument tips and endoscope, a dissection of the left facial compartment from the nasal septum was performed. The view inside the skull base was offered through the dissection. The sagittal view onto the surgical site is shown in Fig. 5.15(d).