Exposure Visualization Accuracy Results.

<p>The mean and maximum over- and underestimation errors in virtually representing the drill cavity (i.e. the surgical exposure) are presented in millimeters (on the y-axis) for each temporal bone phantom (whose index is displayed on the x-axis). Note the differences in errors between the first three models and the last seven models in which higher resolution CT scans were used.</p

The EVADE Interface.

<p>The EVADE interface is shown. Figure annotations (a–f) are displayed in red. In the upper left corner a 3D rendering of the anatomy (in this case a temporal bone phantom) is shown and around it are three orthogonal sections. The green cross designates the current position of the drill tip. The yellow shape represents the drill bit being used (a). The modeled sigmoid sinus (b) and facial nerve (c) are outlined in blue and orange respectively. The virtually drilled cavity is displayed both in 3D as in 2D (d). The two numbers on the bottom give the current distance to the sinus (e) and facial nerve (f).</p

Drill Tracking Accuracy Results.

<p>This table displays results for four separate tracking accuracy experiments on the cylinder and ball phantom in the operating room. Average target registration errors are given in millimeters for the “Pointer” and a drill with “3 mm”, “4 mm” or “5 mm” drill bits attached, for each experiment. Additionally, overall average and maximum target registration errors for each of the instruments are displayed in millimeters in the row “Average” and “Maximum” respectively. “SD” means standard deviation.</p

Virtual Drill Bits.

<p>Drill bits were scanned with high resolution CT and represented as 3D point clouds. On the left is displayed a 3 mm match-head drill bit and on the right a 4 mm drill bit can be seen.</p

Intra-Operative Setup during Temporal Bone Surgery.

<p>This figure shows the typical situation during a trans-labyrinthine approach with a navigated drill (a) on the temporal bone phantoms (b) in the operating room. The surgeon used either the EVADE interface (c) or the standard navigation interface (d). Note the infra-red camera (e) used for tracking.</p

Temporal Bone Phantoms.

<p>This figure shows an example of a plastic temporal bone phantom. On the outside divots (d) were drilled to be used as fiducial markers for registration. On the inside a modeled silicon sigmoid sinus (a) and tumor resembling a vestibular schwannoma (c) were placed. Also, a straight canal was drilled in which a metal rod was placed serving as a modeled facial nerve (b).</p

Illustration of Critical Structure Safety Mantle Implementation.

<p>This figure illustrates the principle of the critical structure safety mantle implementation which EVADE uses to generate timely audiovisual warnings in spite of drill tracking inaccuracies of the navigation machine. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041262#pone-0041262-g005" target="_blank">Figure 5A</a> shows the temporal bone phantom for purposes of anatomical orientation. In <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041262#pone-0041262-g005" target="_blank">figure 5B</a> the bone phantom has been rendered translucent to show the drill bit (in grey) and modeled critical structures; the sigmoid sinus and the facial nerve. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041262#pone-0041262-g005" target="_blank">Figure 5C</a> is a zoomed in view on the critical structures (in white) in which the safety mantle (the orange-golden translucent area) is visible around the critical structures. Note that the safety mantle thickness measured from the surface of the structures is 3 millimeters. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041262#pone-0041262-g005" target="_blank">Figure 5D</a> shows the same situation from a different angle. The drill bit is still outside of the safety mantle. In <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041262#pone-0041262-g005" target="_blank">Figure 5E</a> the surgeon has continued drilling and the drill bit tip (now in red) has entered the safety mantle around the facial nerve. EVADE is triggered to provide audiovisual warnings. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041262#pone-0041262-g005" target="_blank">Figure 5F</a> shows the situation as in 5E from a different angle.</p