Eur Arch Otorhinolaryngol (1997) 254:343-346
W. F r e y s i n g e r
9A. R. G u n k e l
9 Springer-Verlag 1997
9W. F. T h u m f a r t
image-guided endoscopic ENT surgery
Received: 5 August 1996 / Accepted: 19 December 1996
A b s t r a c t Intraoperative three-dimensional (3D) "navigation" has siginificantly improved patient safety during operative procedures on the paranasal sinuses and the frontal
skull base. The ISG Viewing Wand (ISG Technologies,
Mississauga, Ontario, Canada) is now used routinely for
such procedures in our hospital at the present time. Current use with our radiological and intraoperative protocols
has demonstrated a clinical accuracy o f 1-2 mm. Initial
experience with the A R T M A Virtual Patient ( A R T M A
Biomedical, Vienna, Austria) has allowed endoscopic 3D
navigation by using augmented reality techniques and has
been found to be very promising. We present our experience with these systems and discuss the impact of these
unique techniques on computer-assisted surgery (CAS) in
otorhinolaryngology and head and neck surgery.
fit from such systems by extending the limits of a "safe"
area to allow for more complete and radical operative
therapy. Trainees and y o u n g e r surgeons m a y benefit by
providing ongoing orientations to anatomic landmarks
and by being warned about delicate structures that should
not be touched.
Recent advances in computer and software technology
have allowed the development and widespread use o f intraoperative navigation systems. In contrast to neurosurgery, this field is still very new for E N T surgeons. This
report will present our experience with two systems in
performing surgery o f the paranasal sinuses and anterior
skull base.
Materials and methods
Computer-assisted surgery 9ISG Viewing
Wand 9A u g m e n t e d reality Intraoperative navigation 9
Image-guided surgery
Key words
Introduction
Currently available radiological imaging provides the necessary
resolution and quality for intraoperative navigation. The generation of so-called three-dimensional "3D" data, i.e., cubic voxels
with contiguous slices, is necessary. Helical axial scans of the head
from the upper incisors to the frontal sinus are performed to yield
1-mm slices and are used for actual navigation [4]. In this technique, 3D magnetic resonance (MR) sequences [4] are transferred
entirely via the hospital network. Post-processing on a graphic workstation (Allegro, ISG Technologies, Mississauga, Ontario, Canada)
generates a 3D reconstruction of the patient, which is then copied
to the Viewing Wand in the operating room. A final check of the
navigation unit will complete preparations for surgery within 24 h.
When we started "navigation" in our hospital, we exclusively
used radiopaque markers ("X-spots" Beekly Corp, Conn., USA)
which were placed on the patient's head for CT scanning. We now
use almost exclusively our registration device [3], which is essentially based on an upper jaw imprint, and is securely held in place
by vacuum. Patient immobilization during scanning, if necessary,
is achieved with a dedicated head-fixation device [9]; patients are
instructed to keep their eyes shut.
Similar to neurosurgical interventions, surgical procedures in otorhinolaryngology are ideally suited to the use
of intraoperative computer-assisted stereotactic navigation systems. The surgical field is very precisely contained in b o n y structures, so that preoperative imaging
will match exactly any perioperative findings. In both disciplines, a variety of vital structures is located in the surgical field. Especially in the presence o f changed anatomical relationships due to pathological processes or bleeding, intraoperative orientation and guidance represent an
important, if not the most important, supplementary aid
for a surgeon. Even very experienced surgeons can bene-
The Viewing Wand System and its intraoperative use
W. Freysinger (N~). A. R. Gunkel . W. F. Thumfart
ENT Department, University of [nnsbruck,
Anichstrasse 35, A-6020 Innsbruck, Austria
The patient's 3D coordinates are determined with a position-sensitive, articulated mechanical arm, that has 6 degrees of freedom. A
variety of probes (long, short, and bent probes, and straight suction
tubes) is available for navigation. The intraoperative position of a
probe is displayed in axial, coronal, sagittal, and "ultrasound"
views of the 3D data set, and in the patient's 3D reconstruction.
344
More technical details about the navigation system can be found
elsewhere [11].
After introduction of general anesthesia, the patient's head is
placed in a Vogele-Bale-Hohner (VBH) head holder; underpressure repositioning of the mouthpiece is started and counterfixation
is mounted. Hydraulic arms hold the components and facilitate efficient patient immobilization. Registration is performed by touching markers, the registration device, or anatomical landmarks with
the calibrated probe attached to the mechanical arm and subsequent correlation to the appropriate locations in the 3D data set
(Fig. 1). System preparation is completed by verification of registration [3, 4] and surgery is conducted as usual.
A
The Artma Virtual Patient
Fig. 1 Schematic setup of the ISG navigation system for a video
endoscopic procedure. Video equipment (A), computer (B), position sensitive arm (arrow). Fixation fo the patients's head to the
table is shown symbolically (hatched structure). The video-endoscopy unit is not linked to the navigation system
A
B
Fig.2 Schematic setup of the A R T M A System. The video endoscopic equipment (A) is connected to the navigation system (B),
the 3D-digitizer consists of the digitizer itself (C), Hall sensors and
the generator of the magnetic field (arrows)
In addition to 3D CT/MR images, this system allows 3D navigation in 2D medical images, such as X-rays, ultrasound and video.
This is realized by linking a 3D reconstruction of the imaged scene
[5] to CT/MR, or a camera simulation [8] to overlay stereotactic
targets, structures and access pathways onto available images and
live video available in the computer [1]. Most importantly, this
system does not need mechanical fixation of the patient on the operating table. Once the patient is anesthetized, Hall sensors are attached to the patient's head, an endoscope and the instrument. For
navigation, the endoscope's optical system has to be calibrated. [6]
At least six anatomic landmarks, the registration device or fiducials are touched with a stylus and correlated to a specific location
in each of the navigable images [10]. CT-MR registration is performed as usual [11]. Visual inspection of the concordance of calculated and measured points on the live video terminates the system's setup. Surgery is carried out as usual. Prior to the actual intervention the CAS operator and the surgeon jointly define the structures to be visualized in the live video, such as the optimum access
trajectory to a target or a vital anatomical structure to avoid (Fig. 2)
Results
T h u s far, w e h a v e u s e d t h e I S G V i e w i n g W a n d a n d t h e
ARTMA Virtual Patient in a series of 79 interventions
( T a b l e 1). B o t h C T a n d M R d a t a h a v e b e e n u s e d s u c c e s s -
T a b l e 1 Summary of indications for 3D navigational surgery
Indication for surgery
Operations
System
(Pan-)sinusitis
20
ISG
ARTMA
15
5
3
3
FESS
25
ISG
ARTMA
20
5
3
3
5
ISG
ARTMA
5
1
< 1.5
n/a
Samples from the maxillary sinus, the nasal
septum and the sinus Morgagni from the
"Innsbruck Iceman" [6]
Orbital decompression
10
ISG
ARTMA
8
2
< 1.5
3
For intraoperative accuracies approaching
the monitor resolution < 1.5 mm, arbitrarily chosen, resembles the accuracy of a surgeon to quantify the position of an instrument video-endoscopically
Carcinoma (primary and recurrent adenocarcinoma, adenoid cystic carcinoma)
15
ISG
ARTMA
13
2
2
3
4
ISG
ARTMA
1
3
2
3
Biopsies (posterior sphenoid wall [2],
roof of sphenoid, pterygopalatine fossa,
posterior maxillary sinus)
Foreign bodies [aspergillus sinusitis (2 cases)
dental filling in maxillary sinus, ingested
needle in parapharyngeal space]
Mean accu- Remarks
racy (ram)
Tape and VBH head fixation [4] estimated
accuracy
Excessive intraoperative tissue shifting of
the neck did not allow removal
345
Fig.3 Intraoperative screenshot of a biopsy facilitated by the
Viewing Wand in the sphenoid sinus. It shows axial, coronal and
sagittal, and the ultrasound reformatted CT views (counter-clockwise). The tip of the Viewing Wand's probe is located at the center of the crosshairs, which is positioned on the bottom of the sphenoid. The contrast-enhanced CT shows the relation of the surgical
field to the internal carotid arteries. The tumor is seen eroding the
apex of the left orbit
Fig. 4 [ntraoperative video screenshot during the removal of a foreign body with the ARTMA Virtual Patient system: navigation
employs X-ray, CT, and video images. The planned path into the
maxillary sinus (rectangular structures), the target (point) and local coordinate systems in the static view are shown
fully for navigation. The clinical data for arm-based intraoperative localization have been more detailed to date.
W h e n using the V B H headholder and the appropriate registration techniques we have typically reached acccuracies
in the range o f the monitor's resolution.
The following cases exemplify use of both 3D systems.
One patient, 29 years/male, had extensive neurological
deficits due to tumor and required a transnasal, transsphenoidal biopsy of the posterior wall of the sphenoid sinus
to histologically classify the tumor lesion present. A n intraoperative registration accuracy of < 2 m m in all directions allowed us to approach the tumor close to the inter-
Fig. 5 Intraoperative screenshot of the surgery in Fig. 4. A photograph of the live endoscopic endonasal video. The endoscope is
just being inserted through the nostril. The right concha (left structure), a nasal spur (lower right structure), some polypoid structures (upper center) can be differentiated. The endoscope is guided
through the rectangles, symbolizing a bent 3D path, which curves
at the uncinate process (point) to the predefined target
hal carotid arteries (Fig. 3). Navigating with the I S G system's probe confirmed the exact anatomic location of the
arteries so that the procedure was completed without complications. Surgery was completed without complications.
The biopsy revealed an adenoid cystic carcinoma, which
was subsequently resected by neurosurgical staff.
The second patient, 32 years/female, reported headache
with obstructed right nasal breathing and discharge. Imaging revealed a radiodense structure in the right maxillary
sinus and thickened endonasal m u c o s a (Fig. 4). A foreign
b o d y was located in the right maxillary sinus by the
A R T M A system. Planning was executed on CT scans and
a lateral X-ray of the patient. Intraoperatively, a nasal antral
fenestra was created and a = 2 x 3 x 3 m m amalgam dental filling was successfully removed. This was extensively
covered with aspergillus. Surgery was completed without
complications. In this case, the introperative accuracy was
3 mm.
Discussion
In our routine work with the Viewing Wand, we have
achieved mechanical and registration accuracies of 0.2
and < 2 mm, respectively. The registration device [9] allows minimizing intraoperative errors to the resolution of
the Viewing Wand's monitor. For the A R T M A system we
have found accuracies better than 3 mm. This number has
to be estimated, since the intraoperative videoendoscopic
images superimposed with stereotactic information have
to be evaluated.
The Virtual Patient technology was found to be very
promising. The interferences of magnetizable objects with
the magnetic digitizing technology, however, can be han-
346
died satisfactorily [7]. The system has advanced real-time
on-line telesurgery capabilities based on telephone, ISDN,
Ethemet, and Internet [8], as demonstrated by sharing a
CT data set, registration parameters, and the surgical planning of revision sinus surgery between Innsbruck, Austria
and San Diego, California, USA, via ISDN [7].
The two systems studied represent two different stages
of the technical evolution in CAS technology. The ISG
System is widely used in neurosurgery and has already
gained significant attention in ENT surgery [2, 10],
whereas our department has been the first clinical otorhinolaryngologic test site for the ARTMA system. Both systems provide comparable intraoperative accuracy, although the ISG system to date has performed slightly better. However, this is more than compensated by the limitations imposed by the technologic approach chosen for
navigation. The measurement of position needs a dedicated instrument, and the handling of a surgical instrument, if mounted to the articulated arm, is impeded by the
mechanical limitations and the weight imposed by the
arm. We believe the development of detailed application
protocols will allow both 3D navigation systems to
achieve similar accuracies. A comparison of two such different techniques still needs to be done with caution.
The Virtual Patient system is designed to integrate naturally into a video endoscopic procedure without "disturbing" an intraoperative setup by mechanical fixation of a
patient or mechanical arms introduced in the sterile zone.
This represents a state-of-the-art solution for providing
real-time positional information to the surgeon in a realtime endoscopic video. It can be anticipated that the clinical performance of augmented reality in the operating
room will have a substantial impact on the development
of future intraoperative navigation systems.
The use of high-tech navigation in our hands has not
resulted in intraoperative complications induced by system usage. However, the procedures safely performed so
far in highly critical areas (such as in the first patient described) or in facilitating tumor resections suggest the real
value of this technique. Patient safety can be and was
maximized by use of these two navigation systems.
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