An integrated system for planning, navigation and robotic assistance for skull base surgery

Abstract

Background: We developed an image-guided robot system to provide mechanical assistance for skull base drilling, which is performed to gain access for some neurosurgical interventions, such as tumour resection. The motivation for introducing this robot was to improve safety by preventing the surgeon from accidentally damaging critical neurovascular structures during the drilling procedure.

Methods: We integrated a Stealthstation navigation system, a NeuroMate robotic arm with a six-degree-of-freedom force sensor, and the 3D Slicer visualization software to allow the robotic arm to be used in a navigated, cooperatively-controlled fashion by the surgeon. We employed virtual fixtures to constrain the motion of the robot-held cutting tool, so that it remained in the safe zone that was defined on a preoperative CT scan.

Results: We performed experiments on both foam skull and cadaver heads. The results for foam blocks cut using different registrations yielded an average placement error of 0.6 mm and an average dimensional error of 0.6 mm. We drilled the posterior porus acusticus in three cadaver heads and concluded that the robot-assisted procedure is clinically feasible and provides some ergonomic benefits, such as stabilizing the drill. We obtained postoperative CT scans of the cadaver heads to assess the accuracy and found that some bone outside the virtual fixture boundary was cut. The typical overcut was 1-2 mm, with a maximum overcut of about 3 mm.

Conclusions: The image-guided cooperatively-controlled robot system can improve the safety and ergonomics of skull base drilling by stabilizing the drill and enforcing virtual fixtures to protect critical neurovascular structures. The next step is to improve the accuracy so that the overcut can be reduced to a more clinically acceptable value of about 1 mm.

Figure 1

System overview of the image-guided robot for skull base surgery. System components include: modified NeuroMate^® robot in cooperative control mode; StealthStation^® navigation system; 3D Slicer software for intraoperative visualization; and workstation for application logic and robot control

Figure 2

Set-up for cadaver experiment. The surgeon operates the robot-mounted surgical drill in cooperative control mode

Figure 3

Slicer display for intraoperative visualization, showing the location of the cutter relative to the bilateral virtual fixtures

Figure 4

System block diagram showing workstation tasks and interfaces to external systems

Figure 5

Transformation map for the coordinate frames

Figure 6

Phantom experiments. (Left) CT slice view of phantom with foam block; (middle) experimental set-up; (right) machined foam block

Figure 7

Specimen 1. (Left) Preoperative CT cross-section showing virtual fixture (VF). (Right) Postoperative CT cross-section showing uncut bone (U) and overcut (O)

Figure 8

Specimen 2. (Left) Postoperative CT with VFs (original and simplified) in place, showing the overcut (O) and uncut bone (U) of the left side IAC. (Right) The overcut (O) of the right side IAC procedure