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of the contours was off-putting. The surface mesh on the
virtual view was earmarked as a potential area for fur-
ther development, with some finding it confusing or dis-
tracting; others would have preferred a more lifelike
semitransparent surface rendering.
Auditory Alerts
A number of auditory features for critical structure
proximity alerts were upgraded during the trial in
response to suggestions. Subjects were observed to
instinctively shift their gaze toward the source of the
alarm. To reduce this interruption, speakers were placed
directly next to the endoscopic monitor. The first three
participants found the abstract sound alerts (beeps) dis-
tracting and often unhelpful. It was difficult to distin-
guish acoustically which anatomical structure was close
and how far away it was. Auditory icons are sounds that
in some way relate to the reason for alarm. They should
be intuitive and easily learnt. Auditory icons were devel-
oped for the dura and carotid arteries to provide more
information to the surgeon. For example, the sound cho-
sen to represent proximity to a major vessel (carotid
artery) was reminiscent of an arterial Doppler trace.
Structure- and distance-specific alarms then gave the
operator navigational data without additional visual
stimuli or having to look away from the main monitor.
Most of the remaining subjects appreciated this new
feedback medium.
Alert zones were manually contoured and generally
around 2 to 3 mm. There was agreement that this is an
appropriate distance. All subjects thought the alarms
required some form of customization, especially after a
structure had been safely identified. For example, once
they had confirmed the position of the carotid, a con-
stant alarm while they were drilling adjacent to it was
not helpful. Most suggested being able to turn off the
alarms once landmarks and structures were clearly
identified.
Applications
There was strong consensus as to the potential clin-
ical applications for this technology. The combination of
high spatial demand, reduced or absent surface land-
marks, and proximity to critical structures is where
image guidance was thought to be particularly useful.
Any procedure where there is a significant amount of
time spent on a task where these conditions exist would
benefit from live navigational feedback and could ulti-
mately reduce operating time, according to our subjects.
The main tasks identified during this exercise were dril-
ling adjacent to the carotid, particularly near the clival
and petrous portions, and approaching the dura through
thick bone (Fig. 3).
Recommendations
All participants thought that the technology was
ready for clinical trials, but some improvements were
suggested. The ability to customize the settings, particu-
larly the alarm zones, was advised. This included being
able to turn individual structure alerts off once the
structure was successfully identified. The labor required
for anatomical contouring on preoperative imaging was
frequently recognized as a barrier to implementation, as
it would need to be created, or at least verified, by the
operating surgeon.
DISCUSSION
Development of advanced navigational systems is
occurring in many centers worldwide for an ever-expanding
Fig. 3. The drill tip has entered the carotid
alert zone as shown in the virtual and
cross-sectional views. An auditory alert
reminiscent of an arterial Doppler trace is
triggered when the drill is positioned in this
zone to provide structure-specific proxim-
ity information.
Laryngoscope 124: April 2014
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