Technical Issues of Image Guided Surgery
W. Birkfellner
Digital Image Processing Laboratory, Center for Biomedical Engineering and Physics
Medical University Vienna
W. Birkfellner
W. Birkfellner
ImageGuided CMFSurgery
An incomplete list of systems...
ARTMA Virtual Patient RoboDent System DenX IGI System Drill Guides (Materialise, T. Fortin et al.) Modification of
commercial systems like the BrainLAB suite or the Medtronic TREON
... and VISIT
Reviving old VHS Tapes: VISIT in action
W. Birkfellner et al., IEEE Trans Med Imaging. 19(6):616620, 2000W. Birkfellner et al., Clin Oral Implants Res. 12(1):6978, 2001F. Watzinger et al., Plast Reconstr Surg. 107(3):659667, 2001A. Wagner et al., Clin Oral Implants Res. 14(3):340348, 2003
Challenges from a technical point of view
• Imaging – CT protocols & handling of artefacts• Patient – to image registration• Image processing issues – visualization & segmentation• Hardware for imageguided CMF surgery• Workflow optimization • What's about to come ?• Nontechnical challenges ...
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Imaging
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• CT is the modality of choice for dental and CMF surgery
• Streak artefacts stem from the reconstruction process and are difficult to avoid or to be removed• Pantomography is strongly dependent on patient positioning due to the strong perspective and the tomographic distortion of the image• CBCT introduces other artefacts such as truncation and ring artefacts
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Artefacts in CBCT
Truncation and ring artefacts are common ...
Quantitative CT
Homolka P, Beer A, Birkfellner W et al. Radiology, 224(1): 24752, (2002)
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Planning in VISIT
• Planning of implant channels based on available bone volume and density is rather straightforward• For extraoral implants, a more sophisticated interface is necessary
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Tracking & Registrationa Link to the Real World
• Registration: Finding a transformation between the coordinate system of a volume image and the real world• Tracking: Maintaining that registration by measuring motion in 3D by
• optical tracking• electromagnetic probe• alternative techniques
W. Birkfellner et al., Med Phys 25(11):22422248,1998W. Birkfellner et al., IEEE Trans Med Imaging. 17(5):737742, 1998J. Hummel et al., Med Phys 29(10):22052212, 2002
Key issues in Tracking
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• Accuracy and resolution: Optical trackers are rather accurate and still superior to EM probes• Reliability: A free line of sight for an optical tracker always be maintained• Handling: Trackers are cumbersome in general; passive systems have a higher acceptance rate than active (=wired) systems, but are less robust.• Sterilizability: Autoclavation of electronics is difficult, ETO is expensive and timeconsuming
Patient to Image Registration
Point to point registration (Horn) using at least three markers and a point probeerror 0.7 +/ 0.15 mm
Birkfellner W, Solar P, Gahleitner A et al, Clin Oral Implants Res 12(1):6978, (2001)
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Some experiences
Minimally invasive insertion of titanium microscrews is feasible; the markers stay stable for several weeks Increasing the number of markers beyond 3 screws does not influence registration accuracy Exact localisation of screwhead centroids is necessary Mobility of mucosa in atrophic patients caused inaccuracies when using splinttype solutions, even if residual dentition is available
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Image Processing:Segmentation
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Segmentation is not exact – Identification of surfaces depends on algorithms used
Alternative techniques
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Surface registration: Highly dependent on the quality of surface segmentation and the presence of outliers
Surface scanning by laser ranging is hampered by the small visible area of the mucosa
Stab incisions are cumbersome, but give
good results
© by Tactile Technologies, IL
Schicho K, Seemann R, Cohen V et al. J Clin Periodontol. 34(11):9917, (2007)
Splint techniques
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© by DMFR, from Eggers G, Kress B, Rohde S, Mühling J.Dentomaxillofac Radiol. 38(1):2833, (2009)
Problematic in completely edentulous patients Residual elasticity of 2component molding materials is recognizable Segmentation of molding material and mucosa sometimes difficult
Surface Scanning
Has a long history in frameless stereotaxy Complicated for fully intraoral interventions
Result from the Medtronic FAZER surface digitizer – from Schicho K, Figl M, Seemann R et al. J Neurosurg, 106(4):7049, (2007)
Colchester AC, Zhao J, HoltonTainter KS et al. Med Image Anal, 1(1):7390, (1996)
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Tracking technologies for CMF & oral surgery
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32 implants, 5 patients after tumor resection and primary reconstruction
Accuracy: top 1.0 +/ 0.5 mm bottom 1.3 +/ 0.9 mm
Wagner A, Wanschitz F, Birkfellner W et al. Clin Oral Implants Res. 14(3):3408, (2003)
Challenges in tool design Sterilizable electronics are
cumbersome, autoclavation is difficult. Passive markers somewhat solve the problem and are handy, but provide less accurate results when being conatminated with blood Tool geometry (and size) is crucial
West JB, Maurer CR Jr. IEEE Trans Med Imaging. 23(5):53345, (2004)
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An early academic effort Hybrid Tracking
Birkfellner W, Watzinger F, Wanschitz F et al.IEEE Trans Med Imaging. 17(5):73742, (1998)
Combination of electromagnetic and optical sensors to overcome the drawbacks of both technologies
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Looking back Implant insertion 2000
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Implant insertion after hemimaxillectomy
Sealing of the nasopharynx with an obturator prosthesis after radical resection of squamous cell carcinoma
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Restoration after ablative tumor resection
Surgical removal of an osteosarcoma in the mandible Implant insertion in a scapula flap after reconstruction
Wagner A, Wanschitz F, Birkfellner W et al. Clin Oral Implants Res. 14(3):3408, (2003)
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Minimally invasive implant insertion
Wittwer G, Adeyemo WL, Schicho K et al.Int J Oral Maxillofac Implants. 22(5):78590, (2007)
Comparison of VISIT and the Medtronic TREON system. Accuracy ranges from 0.6 +/ 0.5 to 1.0 +/ 0.5 mm for both systems
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Medical AugmentedReality
W. Birkfellner et al., IEEE Trans Med Imaging. 21(8):991997, 2002F. Wanschitz et al., Clin Oral Implants Res. 13(6):610616, 2002W. Birkfellner et al., Phys Med Biol. 48(3):N4957, 2003M. Figl et al., IEEE Trans Med Imaging. 24(11):14921499, 2005
Technology of image injection
Birkfellner W, Figl M, Huber K et al. IEEE Trans Med Imaging.21(8):9917, (2002)
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Linking navigation and augmented reality
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Conclusions & OutlookResearch directions for Computer Aided Surgery in the CMFarea include
Technical developments concerning TRE … Developments for optimized workflow and cost including socioeconomic researchEvaluation of suitable clinical applications
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W. Birkfellner
Acknowledgments
Dept. of CranioMaxillofacial SurgeryDental School ViennaDept. of Diagnostic RadiologyMy Colleagues at the CBMTP… and R. Schulze and the IADMFR for inviting me!
[email protected]://www.zbmtp.meduniwien.ac.at/index.php?id=79