Computer Assisted Radiology
9th International Symposium and Exhibition
Berlin, June 21-24, 1995
Tracking and Guidance Systems
Saturday, June 24, 1995, 11:00
Venue: Universitaetsklinikum Charité, Schumannstr. 20/21,
special support by Prof. D. Bernd Hamm, MD, Director Inst. f. Roentgendiagnostik
D.J.H. Hawkes, PhD, UMDS, Guy's Hospital London (UK)
F.A. Jolesz, MD, Brigham and Women's Hospital, Boston (USA)
Application of the ARTMA Image-Guided Navigation System to Endonasal
A.R. Gunkel, W. Freysinger, W.F. Thumfart, Univ.Klinik f. HNO, Innsbruck;
Truppe, ARTMA Medizintechnik GmbH, Wien (A)
Application of the ARTMA image guided navigation system to endonasal
Gunkel A.R., Freysinger W., Thumfart W. F., Truppe M. J.*
HNO-Universitaetsklinik Innsbruck, Anichstrasse 35, A-6020 Innsbruck, Austria
* ARTMA Medizintechnik GmbH, Am Kanal 27, A-1110 Wien, Austria
We solve the problem of orientation in revision operations with the ARTMA
Virtual Patient® System. It uses state of the art image processing techniques
and a 3D digitizer to find the position of instruments. The realization
of Interventional Video Tomography allows mutual correlation of a video
photo, corresponding anatomical landmarks with CT and/or MRI images. Structures
and access paths to the regions of interest can be defined and fused with
the endoscopic video image in real time. We report our first experiences
with this comfortable an highly reliable tool.
Many surgical procedures in the field of ENT take place in close proximity
to vital structures like the orbit, the skull base, the internal carotid
artery etc. In our clinic we have decided to use computer-assisted navigation
systems to reduce the risk of trauma to vital structures during endonasal
endoscopic procedures. The ARTMA Virtual Patient System finds the position
of a surgical instrument (endoscope) by permanently measuring magnetic fields.
It correlates the position of the surgical instrument, ideally in the range
of 1 mm, to CT- or MR-images and other possible data sources. An important
prerequisite is that the use of Computer-Assisted-Surgery (CAS) does not
extend the time needed for surgery significantly. However, the ARTMA System
is one of several 3D-orientation systems that operate on different technologies
[1,2,3]. Principally, the actual position of the surgical instrument is
shown in the correlating CT- or the MR- images by exploiting the inherent
spatial information of the CT-/MR- images. If properly used, CAS-systems
can be a very helpful tool in the hand of an experienced surgeon but will
never replace his expertise and knowledge.
Material and Method
We used the ARTMA 3D-navigation system mainly in patients having chronic
polyposis of the paranasal sinuses. Preoperatively, an axial CT-scan of
the head was performed extending from the forehead to the hard palate, especially
showing the para-nasal sinuses. The helical scan (3 mm table increment)
was reconstructed in 1 mm non overlapping slices, stored on a WORM optical
disk and transferred to the navigation system. The ARTMA Virtual Patient
 system uses these data without postprocessing. Additionally, it can
handle images provided by other imaging modalities, such as MR, ultrasound,
or X-ray, without modification. Orientation in space is achieved by use
of a 3D-digitizer  which measures magnetic fields with Hall sensors to
determine spatial position and orientation. An electromagnet close to the
head of the patient establishes a magnetic field with known orientation
and strength (see Fig. 1) and defines the reference coordinate system. The
CT data of the patient are calibrated by marking a structure in a slice,
holding a stylus against the corresponding anatomical structure of the patient
and matching it to the appropriate point in two different video photographs
of the patient's face. On this base the patient image transformation can
be realized through the direct linear transformation . The principle
of Interventional Video Tomography (IVT) allows to correlate two dimensional
images supplied by the endoscope to their correlate in the CT or MR slices.
Advanced image processing algorithms and the spatial information of the
imaging modalities yield an exact orientation in space even for the endoscopic
view. Hall sensors attached to the head of the patient, the surgical instrument,
and/or the endoscope trace every change of the magnetic field. Therefore,
the position of the patient and the surgical instrument is known with respect
to the reference magnet near to the patient's head, see Fig. 1. The actual
position of the instrument inside the patient is determined by the computer
and displayed on the screen. Consequently, the patient can be moved in space
During endonasal endoscopic operations the surgeon watches the live endoscopic
video on the computer monitor. He can permanently check every movement of
his instrument (rigid endoscope) by looking at the video image and the corresponding
CT slices displayed by the system at any time. The most sophisticated feature,
though, is that the Virtual PatientTM System allows to mark certain regions
on the screen (either on the CT scan or on the video photograph of the patient)
and to create virtual trajectories of access to the surgical field, leading
the surgeon to the region he is aiming at (Fig. 2). The region of interest
and the defined path are superimposed to the live endoscopic video. The
task of the surgeon is to follow a series of rectangles floating in space.
If he leaves the planned and direct path the rectangles are distorted or
drawn out of his endoscopic view. This indicates that he is leaving the
trajectory of the best approach. The accuracy of the ARTMA System was assessed
by visually judging the quality of the match between the actual anatomical
location of the instrument and its calculated position as displayed on the
video-image. The next release of the software will make measuring of distances
For a well-trained operating team (surgeon, technician, and nurse) the time
needed for calibration data did not increase the operating time significantly.
Good calibration gave an accuracy of 1 - 2.5 mm depending on whether we
used radio- opaque fiducial markers attached to the patient's head or not.
We found that the accuracy of was better with markers and that it was of
crucial importance which anatomical locations we chose for calibration.
It is best to take bony landmarks (i. e. spina nasalis anterior, glabella,
teeth, etc.) instead of soft structures on the skin (cheek, lobule of helix,
The Virtual Patient System requires that the magnetic field should not be
influenced by large masses of metal near to the operating field. A typical
operating room easily meets this condition. Optimal results were obtained
by using a custom- built wooden headrest.
Intraoperatively, it was indeed possible to move the patient's head without
changing calibration. We found that the equipment did somehow naturally
integrate into the usual operative procedure and did not hinder the surgeon
by the introduction of additional instruments, like measuring probes. This
means that with the ARTMA system standard endonasal instruments serve both
as instrument and as probe.
The most useful feature of the system, though, is that the surgeon can follow
a preoperatively defined path to the target. e.g. tumor, skull base, lamina
papyracea, like a pilot. He is guided by colored rectangular frames floating
in space superimposed to the live video-endoscopic images. It is important
to note that this path can lie anywhere in the patient's head. It is not
restricted to lie in "direct sight" of the surgeon; this allows
him to use, say, a 70_ optics of the endoscope and bent instruments. We
actually could measure distances, mark structures, and work in any region
inside the nose or the paranasal sinuses as if we were performing a normal
One of the major advantages of the ARTMA Virtual Patient System is that
both the patient and the instruments can be moved freely relative to each
other without disturbing the calibration. This permits the surgeon to operate
just as normal, moving the patient's head as he deems necessary. This system
opens up a wide range of application possibilities as other media can be
used for correlation, i.e. MRI images, ultrasound images, etc.. We worked
with a first prototype of the ARTMA Virtual PatientTM System; a second release
of the software version is under development and will enhace comfort and
performance of the system. Many more tests are necessary to improve this
systems and introduce it into regular clinical routine. Nevertheless, this
3D-navigation tool is an excellent aid during endoscopic endonasal surgeries.
The ARTMA Virtual Patient System can be termed a 3D video navigation system..
The arrival of even more powerful computers and "intelligent"
software will never replace the experience and the skill of a surgeon. It
is always he, who has to take the ultimate decision about the next step
of a surgical procedure.
1 A. Kurzeja, M. Wenzel, B. Korves, R. Mösges, Dekompression des Nervus
opticus nach Frakturen des Riechschädels mit Hilfe von CAS (Computer-Assisted
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2 K.T. Kavanagh, Applications of Image-Directed Robotics in Otolaryngo-logic
Surgery, Laryngoscope, 104,283-293.
3 S. J. Zinreich, S. A. Tebo, D. M. Long, H.Brem, D. E. Mattox, M. E. Loury,
C. A. Vander Kolk, W. M. Koch, D. W. Kennedy, R. N. Bryan, Frameless Stereotaxic
Integration of CT Imaging Data: Accuracy and initial Applications, Radiology,
188, 735-742, 1993.
4 M. J. Truppe, Augmented Reality in Endoscopic Surgery, presented at Medicine
Meets Virtual Reality III, San Diego, USA, January 19 - 22, 1995.
5 C. F. Hildebolt, and M. W. Vannier, Three-Dimensional Measurement Accuracy
of Skull Surface Landmarks, Am. J. Phys. Anthropol., 76, 497-503, 1988.
6 Y. I. Abdel-Aziz, H. M. Kamara, Direct linear transformation into object
space coordinates in close range photogrammetry. In Proceedings of the Symposium
on Close-Range Photogrammetry, University of Illinois, pp 2 -28, January
Figure 1: Schematic drawing of the intraoperative system set-up. A PC (1)
is connected to a monitor (2), an endoscope(3), and a 3D-Digitizer (4).
The origin of the overall coordinate system is generated by (5). The orientation
of the field lines is shown schematically. The relative position of the
patient (6) and the endoscope (3) or the instrument is measured by Hall-probes
(black cubes). The relevant coordinate systems are shown for the patient
(xp, yp, zp) and the endoscope (xe, ye, ze).
Figure 2: Intraoperative photograph of an endoscopic image, some marked
structures (full points), and the rectangles symbolizing the preoperatively
defined trajectory of approach (path).
© Copyright 1996 Artma. All rights reserved. Last modified
May 6, 1996.