Telepresence in Ear-, Nose-and Throat Surgery

transcript

* Correspondence: email: wolfgang.freysinger@uibk.ac.at, http://homepage.uibk.ac.at/homepage/c531/c53108/index.html,Telephone: +43 512 504 2314, Fax: +43 512 504 5031

Telepresence in Ear-, Nose- and Throat Surgery

Wolfgang Freysingera*, Andreas R. Gunkela, Walter F. Thumfarta, Michael J. Truppeb

a Clinic of Otorhinolaryngology, Clinical Division of General Oto-Rhino-Laryngologic Diseases,University of Innsbruck

Anichstr. 35A 6020 Innsbruck, Austria

b ARTMA AG.Simmeringer Gründerzentrum

Am Kanal 27,A 1110 Vienna, Austria

ABSTRACT

The intraoperative orientation of a surgeon during video-endoscopic endonasal procedures is a challenge.Individual anatomical knowledge and modern 3D-computer assisted navigation technologies provide a maximumof information during surgery (= patient safety). As such, the position of a tool is visualized in the preoperativeradiologic images as the center of cross-hairs in typical axial, coronal and sagittal views of, e.g. of a stack of CTimages. We have implement the augmentation of reality by superimposing the positional data and additionalguiding structures - access paths and delicate structures - to the live video of the surgical site.The currently available telecommunication infrastructure allows to connect any two locations in order to facilitateand allow remotely proctored preoperative planning, consultation and guidance. This allows to provide themaximum of intra-operative information, with an „expert advice“ from a remote specialist.We have been achieving satisfactory results on base of telephone, ISDN, Ethernet and ATM connections and coulddemonstrate that the ARTMA technology provides essential information for a remote expert, who shares the sameinformation as the local surgeon, and can be an essential aid for difficult surgical interventions. The ARTMAKnowledge Guided SurgeryTM can become an important tool for further optimizing surgery.

Keywords: intraoperative navigation, 3D-navigation, computer assisted navigation, augmented reality, ARTMA,telepresence, telesurgery, teleproctoring.

1 INTRODUCTION

1.1 Basics of intraoperative navigation

The special anatomic situation in the paranasal sinuses has always been an extreme challenge for surgeons due to the closeproximity of a variety of delicate and vital anatomical structures, like the anterior skull base, the optic nerve, the internalcarotid arteries, and the clivus. The proliferated use of endoscopes and recently video endoscopes for endonasal procedures hasincreased the demand for exact surgical orientation enormously. There is a variety of publications concerning the intraoperativecomplications of such video-endoscopic procedures, some of which are given.1-3 Since typically only monoscopic views areavailable the depth perception of the view is absent. By extended and intensive training surgeons are able to reliably determinethree-dimensional positions by moving the endoscope or an instrument. However, in cases of revision surgery or extendedpathologies 4 it is not sufficient to have excellent control of an instrument of a tool. In such situations it is extremely importantto possess exact positional information to necessarily achieve the maximum surgical efficiency and optimum patient safety.This is especially true for minimally invasive surgery, as is endoscopic surgery, in ENT, neurosurgery and most recentlylaparoscopic surgery.

To aid the surgeon in these critical decisions - how far resections can go - in the early eighties computer-assisted technologieswere introduced 5 6 7 8 into the Ear- Nose- and Throat (ENT) operating room. In the following we give a brief overview of theimplemented technology.

1.2 Three–dimensional tracking technology

Initially, position sensitive arms were used as three–dimensional digitizing tools to determine the spatial position of the patientand the tip of the instrument (probe). The first work with such a system 7 opened the way to neurosurgery. Contemporarily,magnetic digitizing was implemented independently by 9. Optical digitizing with infrared-emitting diodes started in 199210 andhas now become the standard for practically all surgical disciplines. Ultrasonic digitizing 11,12 and 13,14 have not been pursuedfurther. Due to the improvement of the ultrasound measuring and error handling these devices will reach a broaderimplementation. Magnetic digitizers for surgical navigation are, due to their ease of use and the nature magnetic fields superiorto optical technologies, since they do not need a direct line-of-sight to a detecting camera. However, the magnetization and theresulting distortion of the magnetic field has to be taken into account. 15 16-19 but can be handled in a way that very satisfactoryintraoperative position measurements become possible. With the ARTMA Medscan II System (ARMTA AG, Vienna, Austria)magnetic 3D–digitizing technology has been successfully implemented into oral and maxillofacial, implant dentistry andendoscopic ENT surgery.

Basically, the coordinate space of the three–dimensional preoperative images, the volume of computed tomography (CT) ormagnetic resonance imaging (MR) is connected to the physical patient on the operating table by essentially a rigid–bodytransformation algorithm 20,20 in a way that some points in of the 3D–data set of the patient are correlated to the correspondingpoints on the patient. The patient is either immobilized in the reference frame of the digitizing system, see the Viewing Wandimplementations 21 or the patient carries a reference element of the spatial measuring system 22,22-24. The optimal transformationbetween these two data sets is used for navigation. An optional tool or a dedicated measuring probe can easily be implementedwith a tracking sensor mounted onto it.

With the ARTMA System we can use the magnetic Polhemus Fasttrack (Polhemus, Colchester, VT, USA), the NorthernDigital Polaris (NDI Inc., Waterloo, Ont., Canada), or the IGT Flashpoint (Image Guided Technologies Inc.,Boulder, Colo.,USA) digitizers. A custom specified interface for the use of any other commercial 3D–sensing device is available on request.

1.3 Integration of two–dimensional images into navigation

Apart of inherent three–dimensional data sets of computer–tomography and magnetic resonance tomography two–dimensionalimages of ultrasound and X–ray imaging, digital photos and still videos can be used for intraoperative navigation with the

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ARTMA system. Most commonly, the integration of fluoroscopy into computer–assisted navigation has been realized so farin the majority of the commercially available systems. 25,26 and for a variety of integrated multi modal imaging27. Mostly thisis done with a calibration cage 28; we implement two–dimensional images by means of the 29 and the 30 algorithms. By choosingat least seven well defined and discernible points in the 2D–images a correlation to the „real world“ can be achieved inmillimetric accuracy 22,23 31,32.

These implementations have been widely implemented and tested in photogrammetry and therefore the reader is referred to theliterature given in the cited references.

1.4 Integration of live–video into navigation

To include the live video images into navigation the camera and its optics have to be calibrated. We have implemented twoalternatives of which we regularly use the Direct Linear Transformation algorithm of Abd-el Aziz and Karara 29 in our dailyroutine. For extended accuracy an extended Tsai algorithm 29 can be used. In essence, at least seven points of the imaged bythe camera have to be digitized with a probe of the 3D–camera or with the stylus of the Polhemus digitizer. In a still view ofa scene the tip of the probe is digitized and the world–coordinates and the pixel– coordinates are stored for calculation. Thisprocedure is repeated at least seven times. The stylus needs to be kept stable in space only as long as to guarantee a clear viewwith the camera. The camera itself, of course, needs to be tracked in space with a sensor of the 3D–camera.

Once this is achieved, the calibrated camera can be moved in space freely and the tip of the endoscope, in our case, can be usedas a probe itself. The video is now „stereotaxic“ in the sense that in every frame the spatial positions of a point selected in thestill– or live–view are known.

1.5 Augmentation of reality

With all the transformations determined in the previous sections the imaging modalities used for navigation (2D and 3D) canbe linked together, so that a position in the patient can be visualized in all the images chosen. The display is such that anygraphic structure (points, lines, cross hairs and so forth) can be defined according to the surgeon´s needs. The transformationsimplemented can be inverted, so that a selected point in one imaging modality with its coordinates

(x1,y1,z1)modality1 ! (x2,y2,z2)modality2

which allows to define additional structures, mostly lines, which mark the boundaries of critical anatomical areas or an optimaltrajectory of approach. The drawing of is done within the Medscan II application and is as simple and intuitive. Once a line,say the course of an aberrant internal carotid artery at the lateral wall of the sphenoïd sinus is outlined, it is shown in all theother images used. These images can now be used to optimize the graphical definition interactively; this is very helpful, sincethe exact creation of three–dimensional structures in two–dimensional images on a computer monitor is extremely difficult dueto the inherent perspective of the images.

Typically we use two (relatively) orthogonal video images of the patient´s face to have an intraoperative control of theplausibility of the structures defined. It is quite difficult to obtain suitable orthogonal views of the patient intra-operatively,which satisfy the needs of navigation under intraoperative, partly sterile conditions; however, orientation in the two images ismore convenient if the views are more or less orthogonal to each others.

1.6 Implementation of Telepresence

The selection of Macintosh as a computing platform is nowadays historical. Practically all systems now provide and realize thegeneration of „movies“ and many clients and servers provide real–time Internet video, TV and movie previews. When westarted to implement20 the Telepresence feature in the Medscan System we chose Macintosh for its graphics capabilities andthe at that time emerging Apple Quick TimeTM software, which is now ubiquitous. The Apple software has been integrated an

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modified so as to carry spatial information on the track reserved for sound. The Medscan application streams the video of theoperating site into the network chosen. The streaming video technology used is a proprietary ARTMA development, howeverfor simplicity, it resembles the Apple Quick TimeTM technology.

Medscan can use plain telephone lines, ISDN lines, bundled ISDN lines, Ethernet, ATM, xDSL and any othertelecommunication available, like cell phones, GPRS cell phones, and when available, UMTS cell phones.

Basically, when the intraoperative registration is completed and navigation is used successfully intra–operatively, thebroadcasting of the surgery is turned on. This means that the „stereotactic video“ is streamed into the Internet from a knownIP number. Only clients in possession of the dedicated intraoperative navigation software and the required permission to accessthe actual IP number (i.e. the surgery) are allowed to connect and view the video. The Apple Quick TimeTM Conferencingsoftware has been integrated to the Medscan application and in the background manages the connection, the buildup, and thehandshake between the two sites. For the user, and this is especially true for intraoperative applications, extreme robustnessand simplicity is the ultimate goal; and this is broadly supported by this tool. Prior to any remote counseling the two sites mustpossess the same medical data sets. This can be done by any means, like disks, ftp, telnet, email, whatever facility is availableand useful. One site needs to prepare a surgical plan with an access trajectory, if desired, anatomical annotations and graphicalsuperstructures to the data sets as outlined above. This surgical plan needs to be exchanged between the two sides. Once thetechnicalities of establishing the communication are established, the remote expert can log in to the local site.

In the following we briefly address the telecom media used so far and sum up our experiences therewith. We do not go intodeep details of the various communication possibilities, since the ARTMA technology in essence realizes a simple TCP/IPconnection on base of the communication chosen.

1.6.1 Plain telephone lines

The line is used to connect to an Internet provider via modem. Due to the small bandwidth of connecting via modem only verylow resolution and slow moving video sequences could be transmitted. If the video is not used and only the positional data isused for orienting the remote expert, sufficient information can be transmitted so as the expert is enabled to follow themovements of a tool or of a probe in the preoperative data set of the patient, in which all graphical structures are shown inexactly the same way as in the surgical room. If two computers were connected directly via a modem, the delays andcongestions of the Internet can be avoided. However, plain telephone is not used any more for surgical consultation with theARTMA Medscan System.

1.6.2 ISDN

Similar to the above, but the ISDN data line provides a guaranteed 2x64 kbit s-1 baud rate which allows a preliminarysatisfactory transmission of the live video of the surgical site. Direct connection of the two computers, again, providemaximum accessibility. We have, other than that, realized a leased line from an Austrian telecommunications provider from thesurgical computer to the remote expert´s one terminated with an Internet Router, so that both computers need only to use theon–board Ethernet card to connect to the router. Using ISDN provides a widely available communication network which isrelatively stable and economic.

1.6.3 Bundled ISDN

Similar to the above, but high quality video transmission can be achieved if at least three 2x64 kbit s-1 lines are used. Thedrawback of these solutions is the available bandwidth (not for 1.6.3), reliability and stability of the connection33,34.Connections inside Europe are relatively unproblematic, but transatlantic connections need long and careful planning andtechnological cross-checks due to the different norms implemented. 1.6.4 Ethernet

This is the most widely available communication technology and the easiest one to use. In our hospital a 100 base T Ethernetnetwork is implemented which is bridged to the Austrian broad–band (155 Mbit s-1) network. So far, a sufficient bandwidth is

available for our telepresence application. The inherent structure of the TCP/IP protocol underlying the use of Ethernet is themost severe drawback of this communication means: the available bandwidth has to be shared with all potential other users.In the worst case the broadcasted video gets „congested“ in the network. In our special case we tested the broadcasting –receiving within the same segment of the network and could get a suitable quality (in the sense of resolution and framerepetition rate) of the received video signal. Most conveniently, Ethernet easily hooks up to the Internet and is the mosteconomic technology with respect to telecommunication costs.

1.6.5 ATM

With the Asynchrounous Transfer Mode networking the ideal platform for the implementation of telepresence in surgery hasbeen found. It provides a stable, scalable communication which assigns the application a certain bandwidth and keeps thisreserved. Therefore, the advantages of the point–to–point connection can be exploited with the IP over ATM without thedrawbacks of the IP protocol. No other users are connected and the full assigned bandwidth can be used. This ensures the besttransmission quality of the live video. The pricing and the scarce distribution, however, pose some limiting factors on thecommon use of this technology. In intranet solutions ATM is widely available, whereas for metropolitan networks and widearea networks currently (y2k) the telecommunications provider charge substantially for a leased ATM line both forinternational and national networks.

1.6.6 xDSL

Both Symmetric and Asymmetric Digital Subscriber Line technology can be used with the ARTMA system. However, theavailability of the xDSL lines is too small to currently further pursue a development in this direction. It can be, clearly, usedlike any other communications network.

1.6.7 Cell phones, GPRS cell phones, UMTS cell phones

Cell phones can be used principally, but the small bandwidth of 9600 baud does not allow the transmission of video, onlythe positional data during surgery can be transmitted. If no video of the operating site is necessary, a simple positionalcontrol of the tool´s position by the expert will be sufficient.

General Purpose Radio Service has recently been implemented in Austria, but restrictions similar to plain cell phones applyto this technology.

The Universal Mobile Telephone Standard will allow an efficient transmission of video in real–time from the surgicaltheater to the remote expert with convenient video quality. With the implementation of eventual compression algorithms ateleconference can be implemented simultaneously and thus a real–time maximum of support of a local surgeon willbecome possible. Unfortunately, no real implementation of UMTS is available.

2 RESULTS AND DISCUSSION

We have been using this technique on the base of plain telephone, ISDN, Internet and ATM networks. The applicationprovides maximum information and real-time behavior with broadband-networks for the transmission of live-video and surgicaldata.

Figure 1: Intra operative setup showing thepatient with 3D-tracking, navigation unit andsurgical equipment and patient alreadyanaesthetized. The patient is being registratedto the navigation system. In the unsterile phaseanatomical points are touched with the stylusof the Polhemus tracker and these anatomicalpoints are correlated to the appropriate pointsin the preoperative images. The video unit iswheeled in after completion of the registrationprocess. Note that the registration process is atwo-person procedure.

Figure 2: Detail of the registration process andthe patient tracking. The patient wears thenon–invasive VBH-mouthpiece 35 top which asensor of the Polhemus tracker is mounted. Bymeans of the mouthpiece a fixation of thepatient to the operating table and the origin ofthe magnetic field is not necessary. Surgery isthus not impeded by the addition of3D–assisted surgery. The two side bars of theVBH-mouthpiece carry radiopaque markerswhich serve as well–defined registrationpoints.

Figure 3: Intra operative screenshot duringnavigation with the ARTMA Medscan Systemin the operating room as seen be the localsurgeon. The display chosen contains thepreoperative CT images (left), intraoperativestill videos of the patient as lying on theoperating table (top row, frontal, left and rightviews) and the live endoscopic video during avideo endoscopic removal of polyps at theethmoidal cells, just in front of the sphenoidsinus. All images show the defined access pathas a series of circular structures combined witha line - similar to a tunnel - floating over allimages used. In the live video only these partsof the graphics in front of the camera areshown. The CT images and the still videosshow a dot which represents the tip of a tool,viz. the endoscope. Top right the status of thesensors is shown, four are used and their status

is ok. The rest of the windows are drawing tools and buttons for choosing probes (top left). Behind the CT window thedefinition of the surgery by means of a hierarchical tree is shown. Here the relations between the patient, the groups of images,the sensors and the camera are defined. This setup has been found to be the most convenient one for 3D–assistedvideo–endoscopic ENT procedures.

Figure 4: „Intraoperative“ screenshot as seenby a remote counselor with the ARTMAMedscan System. Essentially, the sameinformation from the figure above is presentedin the view of the remote expert. Thedifference between both views is the missinggraphic overlay in the live endoscopic video.The video transmission was done with minimalcompression (slowest update rate of theframes) to demonstrate the achievable qualityof the video with a 100 Mbit s-1 Ethernet LAN.

The ARTMA Medscan II system is builtentirely from off–the–shelf–components and uses standard software on a high-end Apple computing platform. We have been using working solutions on a large–scale realization20 and routinely on a portable Apple G3 notebookcomputer36. And both systems permit a good realization of Telepresence with the ARTMA Medscan system.

ACKNOWLEDGMENTS

We thank the departments of Radiology I & II of the University hospital of Innsbruck for the never ending support and aid ingenerating suitable data sets for navigation, especially the radiologic technologists and the nurses for their patience. The

cooperation of the staff in our operating room willing to undergo and experiment with new systems is most valuable.This work was in part realized by a grant-in-aid by the Austrian National Bank by the Jubiläumsfonds under grant No 7188and by a grant of the Daniel-Swarovski-Fund for the University of Innsbruck for the Year 2000.

REFERENCES

1. R. Keerl, J Stankiewicz, R Weber, W. Hosemann, W. Draf, "Surgical Experience and Complications During EndonasalSinus Surgery.", The Laryngoscope 109, pp. 546 - 550, 1999.

2. J. B. Kinsella, K. H. Calhoun, J. J. Bradfield, J. A. Hokanson, B. J. Bailey, "Complications of endoscopic sinus surgeryin a residency training program", Laryngoscope 105, pp. 1029 - 1032, 1995.

3. H. Rudert, S. Maune , C. G. Mahnke, "[Complications of endonasal surgery of the paranasal sinuses. Incidence andstrategies for prevention]", Laryngorhinootologie. 76 , pp. 200 - 215, 1997.

4. A. R. Gunkel, W. Freysinger, W. F. Thumfart, Endoscopic Sphenoethmoidectomy (P to A), 183, Mosby, St. Louis(MO), USA, 1998

5. R. Mösges, G. Schlöndorff, "A new imaging method for intraoperative therapy control in skull-base surgery",Neurosurg.Rev. 11, pp. 245 - 247, 1988.

6. H. Reinhardt, H. Meyer, E Amrein, "A computer-assisted device for the intraoperative CT-correlated localization ofbrain tumors.", Eur.Surg.Res. 20, pp. 51 - 58, 1988.

7. S. J. Zinreich, S. A. Tebo, D. M. Long, H. Brem, D. E. Mattox, M. E. Loury, Kolk CA vander, W. M. Koch, D. W.Kennedy, R. N. Bryan, "Frameless stereotaxic integration of CT imaging data: accuracy and initial applications",Radiology 188, pp. 735 - 742, 1993.

8. M. M. Goldsmith, R. D. Bucholz, K. R. Smith, N. Nitsche , "Clinical applications of frameless stereotactic devices inneurotology: preliminary report", Am.J.Otol. 16, pp. 475 - 479, 1995.

9. E. Watanabe, T. Watanabe, S. Manaka, Y. Manayagi, K. Takakura, "Threedimensional digitizer (Neuronavigator):New equipment for computed-tomography guided sterotaxic surgery.", Surg.Neurol. 27, pp. 543 - 547, 1987.

10. L Klimek, R. Mösges, M. Bartsch, "Indications for CAS (Computer-Assisted Surgery) systems as navigation aids inENT-surgery.", Lemke, H. U., Rhodes, M. I., Jaffe, C. C., and Felix, R.358 - 361, Springer, Berlin, Germany, 1991

11. N. Nitsche, M. Hilbert, G. Strasser, H. P. Tümmler , W. Arnold, "Einsatz eines berührungsfreien computergestütztenOrientierungssystems bei Nasennebenhöhlenoperationen. I. Technische Grundlagen der Sonarstereometrie.", Oto-Rhino- Laryngologia Nova 3, pp. 57 - 64, 1993.

12. N. Nitsche, M. Hilbert, G. Strasser, H. J. Schulz, A Wunderlich, W Arnold, "Einsatz eines berührungsfreiencomputergestützten Orientierungssystems bei Nasennebenhöhlenoperationen. II. Anatomische Studien und ersteklinische Erfahrungen.", Oto- Rhino- Laryngologia Nova 3, pp. 173 - 179, 1993.

13. E. M. Friets, J. W. Strohbehn, J. F. Hatch, D. W. Roberts, "A frameless stereotaxic operating microscope forneurosurgery", IEEE Trans.Biomed.Eng. 36, pp. 608 - 617, 1989.

14. D. W. Roberts, J. W. Strohbehn, J. F. Hatch, W. Murray , H. Kettenberger, "A frameless stereotaxic integration ofcomputerized tomographic imaging and the operating microscope", J.Neurosurg. 65, pp. 545 - 549, 1986.

15. W. Birkfellner, F. Watzinger, F. Wanschitz, G. Enislidis, C. Kollmann, D. Rafolt, R. Nowotny, R. Ewers, H.Bergmann, "Systematic distortions in magnetic position digitizers", Med.Phys. 25, pp. 2242 - 2248, 1998.

16. S. J. Goerss, P. J. Kelly, B. Kall, S. Stiving, "A stereotactic magnetic field digitizer", Stereotact.Funct.Neurosurg. 63,pp. 89 - 92, 1994.

17. A. Kato, T. Yoshimine, Y. Tomita, T. Ikeda, K. Harada, H. Mogami, "A frameless, armless navigational system focomputer-assisted neurosurgery.", Neurosurg. 74, pp. 845 - 849, 1999.

18. A. D. Milne, D. G. Chess, J. A. Johnson, G. J. King, "Accuracy of an electromagnetic tracking device: a study of theoptimal range and metal interference [see comments]", J.Biomech. 29, pp. 791 - 793, 1996.

19. J. J. Stone, B. L. Currier, G. L. Niebur, K. N. An, "The use of a direct current electromagnetic tracking device in ametallic environment", Biomed.Sci.Instrum. 32, pp. 305 - 311, 1996.

20. K. S. Arun, T. S. Huang, S. D. Blostein, "Least-Squares Fitting of Two 3-D Point Sets.", IEEE Trans.Pattern Analysisand Machine Intelligence 9, pp. 698 - 700, 1987.

21. W. Freysinger, A. R. Gunkel, R. Bale, M. Vogele, C. Kremser, G. Schön, W. F. Thumfart, "3-Dimensional Navigationin Otorhinolaryngological Surgery with the Viewing Wand", ANN.OTOL.RHINOL.LARYNGOL. 107, pp. 953 - 958,1998.

22. M. Truppe, F. Pongracz, O. Ploder, A. Wagner, R. Ewers, "Interventional Video Tomography.", Proc.SPIE 2395, pp.150 - 152, 1995.

23. W. Freysinger, M. J. Truppe, J. Maierbäuerl, F. Pongracz, A. Gunkel, W. F. Thumfart, ""Spatial Annotations" inInterventional Video Tomography: optimizing frameless stereotactic surgery.", H.U.Lemke, M. W. Vannier K.Inamura795 - 798, Amsterdam, Elsevier, 1997

24. M. J. Truppe, W. Freysinger, A. R. Gunkel, W. F. Thumfart, "Remote-guided surgical navigation in ENT Surgery.",Stud.Health Technol.Inform. 29 , pp. 280 - 282, 1996.

25. R Metson, R. E. Gliklich, M Cosenza, "A comparison of Image Guidance Systems for Sinus Surgery", Laryngoscope108, pp. 1164 - 1169, 1998.

25. E. W. Sargent, R. D. Bucholz, "Middle cranial fossa surgery with image-guided instrumentation.", Otolaryngology -Head and Neck Surgery 117, pp. 131 - 134, 1997.

26. P. Jannin, O. J. Fleig, E Seigneuret, C. Grova, X. Morandi, J. M. Scarabin, "A data fusion environment for multimodaland multi-informational neuronavigation.", Comput-Aided-Surg 5, pp. 1 - 10, 2000.

27. A. Hamadeh, S. Lavallee, P. Cinquin, "Automated 3-dimensional computed tomographic and fluoroscopic imageregistration", Comput.Aided.Surg. 3, pp. 11 - 19, 1998.

29. Y. I. Abdel-Aziz, H. M. Karara, "Direct linear transformation from comparator coordinates into object spacecoordinates in close-range photogrammetry.", Symposium on close-range photogrammetryAmerican Society ofPhotogrammetry1 - 18, American Society of Photogrammetry, Univ. of Illinois at Urbana-Champain, 1971

30. H. C. Longuet-Higgins, "A computer algorithm for reconstructing a scene from two projections.", Nature 293, pp. 133 -135, 1981.

31. F. Gazzani, "Performance of a 7-parameter DLT method for the calibration of stereophotogrammetric systems using 1Dtransducers.", J.Biomed.Eng. 14, pp. 476 - 482, 1992.

32. H. M. Karara, Y. I. Abdel-Aziz, "Accuracy Aspects of non-metric imageries.", Phtotogrammetric Engineering 1974,pp. 1107 - 1117, 1974.

33. R. Ewers, W. Thumfart, M. Truppe, O. Ploder, A. Wagner, G Enislidis, N. Fock, A. R. Gunkel, W. Freysinger,"Computed navigation in Cranio-Maxillofaxial and ORL-Head and Neck Surgery: Principles, Indicatiions, andPotentials for Telepresence.", J.Cranio-Maxillofac.Surgery 24, pp. 9 - 9, 1996.

34. R. Ewers, W. F. Thumfart, M. J. Truppe, W. Freysinger, A. Gunkel, M. Millesi, J. Maierbäuerl, F. Pongracz, "Livetelepresence surgery.", Alpbacher Technologiegespräche, "Der Mensch im Netz", Europäisches ForumAlpbachAlpbach, Österreich, 1996

35. R. J. Bale, A. Martin, M. Vogele, W. Freysinger, P. Springer, and S. M. Giacomuzzi. The VBH Mouthpiece - ARegistration Device for Frameless Stereotaxic Surgery. Radiology 205[S], 1107-1107. 1997.

36. W. Freysinger, "A full 3D-navigation system in a suitcase.", Lemke, H. U., Vannier, M. W, Inamura, T, and Farman,A. G.640 - 644, Amsterdam, Elsevier, 1999

Telepresence in Ear-, Nose-and Throat Surgery

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