=Paper=
{{Paper
|id=Vol-1477/paper8
|storemode=property
|title=Auditory support for navigated radiofrequency ablation
|pdfUrl=https://ceur-ws.org/Vol-1477/Proceedings_CURAC_2013_Paper_8.pdf
|volume=Vol-1477
|dblpUrl=https://dblp.org/rec/conf/curac/BlackI0RH13
}}
==Auditory support for navigated radiofrequency ablation==
https://ceur-ws.org/Vol-1477/Proceedings_CURAC_2013_Paper_8.pdf
Auditory support for navigated radiofrequency ablation
D. Black1,2, J. Al Issawi², C. Hansen², C. Rieder², H. Hahn²
¹ Jacobs University, Bremen, Germany
² Fraunhofer MEVIS, Institute for Medical Image Computing, Bremen, Germany
Contact: david.black@mevis.fraunhofer.de
Abstract:
Radiofrequency ablation is applied to treat a lesion using a needle inserted into the patient, which delivers local ra-
diofrequency energy. Guided surgical methods allow surgeons to view the placement of the needle in relation to the
patient to aid in guiding the tip of the needle to the target point. Unfortunately, such methods require that surgeons
remove attention from the patient in order to receive guidance information from a screen. We introduce a novel
method to align and insert an ablation needle using auditory display, allowing the surgeon to retain attention on the
patient. First evaluation results show that novice users can successfully guide a needle towards a target point using
primarily auditory display. We hypothesize that successful auditory display will lead to increased attention on the
patient and reduce unnecessary operator head and neck movements.
Keywords: auditory display, radiofrequency ablation, computer-assisted interventions
1 Problem
Radiofrequency ablation is used to locally apply heat to malignant lesions and destroy them. The task requires the phy-
sician to place the tip of the needle on the surface of the patient, aligning the needle to a pre-planned angle, and then in-
serting the lesion to a sufficient depth to place the tip of the needle inside the lesion. After the tip of the needle has been
placed inside the lesion, radiofrequency energy is applied for a specified duration, effectively destroying the lesion. This
process may be repeated and applied to multiple lesions in the patient.
To aid the physician in transferring preinterventional needle placement planning to the operating environment, naviga-
tion systems have been developed [1] to display the position of the ablation needle with respect to the patient’s body in
3D space. This information is either displayed on a screen or projected directly on the patient [2], [3]. These navigation-
al methods, however, have several limitations. Screens in the operating room require that the surgeon remove attention
from the patient to observe guidance information elsewhere in an operating environment already overloaded with visual
cues [4]. Displaying guidance information onto the patient by means of video projectors or lasers [3] onto the local area
of interest is interrupted by surgeon’s hand and instrument movements. In addition, no instant notification of progress or
completion is given when the surgeon inserts and reaches the target lesion.
We hypothesize that the introduction of auditory display to the task of ablation needle placement can fill a void in navi-
gated interventions by allowing the physician to keep focus on the patient during the three primary ablation needle
placement tasks of tip placement, shaft alignment, and insertion towards the target lesion. Auditory display has been
used in anesthesia [5] but is very uncommon as a modality for navigated interventions. Woerdeman et al. [6] and Han-
sen et al. [7] have described basic evaluations of employing auditory display for navigated surgery using phantom mod-
els.
2 Materials and Methods
Navigation System: Currently, visual guidance cues for radiofrequency ablation employ a crosshair and both a small
and a large circle to relay the position of the needle tip and the angle of the shaft [3] (Fig. 1). The distance of the small
circle to the crosshair origin denotes the distance of the tip of the needle to the planned insertion point (when within 30
mm from the insertion point), and the distance of the large circle denotes the distance of the shaft to the planned inser-
tion angle. When both tip and shaft angle are correct, then the needle is ready for insertion. The insertion depth and tar-
get are visualized as a vertical progress bar showing the distance of the tip to the lesion goal.
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Figure 1: Left: Phantom model with ablation needle. Right: Model of visual alignment aid for tip and shaft
Auditory Display: The auditory display extension to the existing navigation system utilizes the same crosshair paradigm
as the visual method, transmitting the distance of the tip and the shaft angle in two dimensions relative to the crosshair
origin. In addition, the insertion depth is transmitted in one dimension. Two auditory display methods were developed to
aid tip placement and shaft alignment. Both methods may be used for both tip placement and shaft alignment.
Figure 2: Three steps towards final ablation needle insertion
The auditory methods were designed to correspond to tasks being completed in sequence: tip placement, shaft align-
ment, and finally needle insertion (Fig. 2). In the first auditory method (Fig. 3, left), two repeated pulses of different
pitches (260 Hz and 520 Hz, respectively) are played alternatively. Changes in absolute distance to the y-axis (for tip,
between 30 and 0 mm from origin) are linearly mapped to speed between pulses, beginning slowly at the left and right
edges (4 pulses per second), progressing faster towards the center (10 pulses per second). Changes in absolute distance
to the x-axis are mapped to the change in pitch of the alternating pulses (at aforementioned frequencies), which con-
verge towards the center, much like tuning a guitar using a reference tone. At the top and bottom edges of the local area
within 30 mm distance to origin, the pitches are spaced one octave apart. When approaching the center, the lower-
pitched pulse rises in pitch until it reaches the same pitch as the higher pulse. When the tip or shaft is within a defined
distance, a confirmation tone is played (a bank of three sine waves with amplitude modulation of 2 Hz), signaling to the
user that the tip placement or shaft alignment is acceptable.
Figure 3: Left: Auditory display methods 1 and 2
In the second auditory method (Fig. 3, right), a single repeating pulse is played. Changes in absolute x distance (from 30
to 0 mm) are linearly mapped to both speed between pulses (from 4 to 10 Hz) and pitch of each pulse. The auditory
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method requires a two-step movement. First, the user approaches from either the left or right side of the local area, first
aligning the tip or shaft so that it is along the y-axis. Second, once the tracked element is on the y-axis (or, i.e., within a
defined distance), a second pulse replaces the first, with similar speed between pulses but a higher pitch mapping (one
octave higher). Thus, the user approaches from either side and when near or on the y-axis, proceeds to approach the
center. This division of movement allows the user to concentrate on one degree of movement at a time.
Insertion depth is transmitted via two alternating tones with an interval of separation of one octave (between 520 and
1040 Hz) before insertion and rising to equal pitch when reaching goal depth. When the tip of the ablation needle reach-
es the target lesion, and bell tone is played (a recorded sample of a dinner-style bell). Removal of the needle from the
body may also be guided using the same insertion auditory display method albeit in reverse.
Evaluation: A preliminary evaluation with two females and six volunteers was conducted using a think-aloud method to
encourage active responses about what users were doing, thinking and feeling (according to Lewis [8]). All participants
were scientific researchers with no direct experience with either navigated radiofrequency ablation or the auditory dis-
play methods. Of the eight subjects, none claimed to be particularly musical, although one participant had basic
knowledge of digital audio synthesis.
Test participants were first shown the navigation system and then introduced to each of the audio methods. A short ex-
perimental session occurred, after which the subjects completed each task: positioning the tip, adjusting the angle of the
handle, and inserting the needle until the target had been reached. This was repeated for both audio and visual modali-
ties. Using the video screen was also permitted during auditory guidance.
3 Results
We present a new auditory display for navigated radiofrequency ablation. A post-experimental analysis of written and
verbal comments of the subjects indicates that subjects were comfortable with both the visual and the auditory modali-
ties. All subjects claimed the auditory methods to be at least as precise as the visual methods. Subjects noted that the
tasks of placing the tip, aligning the shaft, and inserting the needle were easier to accomplish and provided more confi-
dence than with the visual method, although many participants used the video screen at the end of each auditory-guided
task as a means of confirmation that the needle was correctly placed. For tip placement and shaft alignment, more par-
ticipants preferred auditory method 2 because it divided the guidance into sequential x-axis, then y-axis movement in-
stead of transmitting both simultaneusly. For needle insertion, all participants felt confident in stopping the insertion
motion based on the auditory display.
One cited disadvantage of the auditory method was that it only provides sequence-wise guidance – for instance, no
guidance for the tip placement is given during shaft alignment and needle insertion. None of the participants was an-
noyed by the sounds. All participants understood that sound speed and pitch reflected the urgency of the current posi-
tion. However, participants suggested choosing more instrumental timbres rather than basic synthesized tones.
4 Discussion
This work has presented a novel method to aid physicians complete radiofrequency ablation needle placement tasks us-
ing auditory display. Two methods were evaluated for tip placement and shaft alignment, and one method for needle
insertion.
The proposed method for auditory display opens up completely new possibilities for navigated interventions, but it is
not without drawbacks. Whereas the recent concept of navigated interventions is solely based on the visualization of
image data and planning models, no explicit navigation commands are provided through these visual methods. Inci-
dentally, this eases the clearance of surgical navigation systems for clinical trials because the navigations systems pro-
vide only implicit navigation support. With auditory display, explicit navigation commands and notifications can be
provided even if the surgeon does not look on the screen. Future evaluations of such systems during clinical interven-
tions must be carefully prepared with regard to legal and ethical requirements. In addition, the registration errors of de-
formable organs must still be addressed before such methods can be practically applied.
In summary, the methods developed in this work contribute to the field of computer-assisted interventions and have the
potential to improve the safety of radiofrequency ablations by helping physicians keep focus on the patient instead of a
computer screen. While auditory display for radiofrequency ablation needle guidance is not meant to completely replace
visual guidance, it could become a useful extension to reduce physician stress and improve the overall interaction with
such needles.
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