Prof. Wolfgang Birkfellner Profile

Prof. Wolfgang Birkfellner

Associate Professor at Medical University Vienna

SPIE Involvement:

Author

Publications (37)

Proceedings Article | 29 March 2024 Poster + Paper

Source-detector trajectory optimization for customized CBCT field of view extension using simulated annealing algorithm

Hannah Jungreuthmayer, S. M. Ragib Shahriar Islam, Ander Biguri, Gernot Kronreif, Wolfgang Birkfellner, Sepideh Hatamikia

Proceedings Volume 12928, 129281S (2024) https://doi.org/10.1117/12.3006176

KEYWORDS: Mathematical optimization, Cone beam computed tomography, Kinematics, Image quality, Algorithms, Image quality standards, Visualization, Tomography

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Cone Beam CT (CBCT) has become a routine clinical imaging modality in interventional radiology. Extended Field of View (FOV) CBCT is of great clinical importance for many medical applications, especially for cases where the Volume of Interest (VOI) is outside the standard FOV. In this study, we investigate FOV extension by optimizing customized source-detector CBCT trajectories using Simulated Annealing (SA) algorithm, a heuristic search optimization algorithm. The SA algorithm explores different elliptical trajectories within a given parameter space, attempting to optimize image quality in a given VOI. Kinematic constraints (e.g., due to collisions of the imager with the patient or other medical devices) are taken into account when designing the trajectories. For optimization process, a digital XCAT body phantom was used in which three lesions were placed at extreme positions in the phantom that could not be imaged with the standard circular trajectory. The volume around each lesion was considered as VOI. The geometry of Philips Allura Xper C-arm was considered for simulation. Tomographic Iterative GPU-based Reconstruction (TIGRE) and Universal Quality Index (UQI) were used for image reconstruction and image quality assessment, respectively. Our results showed that proposed trajectories could achieve a UQI of 0.9148, 0.9681, and 0.9632 at the respective three VOIs, which was significantly better image quality compared with circular trajectory (0.5960, 0.4892, and 0.4798 for the three VOIs). In addition, the FOV extension achieved for the three optimized source-detector trajectories was 28.75%, 23.57%, and 22.49%, respectively. Our experimental results have shown that our proposed customized trajectories can lead to an extended FOV and enable improved visualization of anatomical structures in extreme positions while taking into account the available kinematic constraints. This study offers a new approach to improve the diagnostic capabilities of CBCT imaging, thus providing valuable insight into improving patient care in CBCT imaging.

Proceedings Article | 4 April 2022 Presentation

Possibility assessment of CBCT metal artifact reduction based on PICCS reconstruction and trajectory optimization

Sepideh Hatamikia, Ander Biguri, Gernot Kronreif, Joachim Kettenbach, Tom Russ, Wolfgang Birkfellner

Proceedings Volume 12034, 120340W (2022) https://doi.org/10.1117/12.2610627

KEYWORDS: Metals, Reconstruction algorithms, Tumors, Image quality standards, Image quality, Diagnostics, Detection and tracking algorithms, Computed tomography, Compressed sensing, Collision avoidance

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Proceedings Article | 3 March 2017 Paper

Ultrasound guidance system for prostate biopsy

Johann Hummel, Reinhard Kerschner, Marcus Kaar, Wolfgang Birkfellner, Michael Figl

Proceedings Volume 10135, 101352A (2017) https://doi.org/10.1117/12.2254004

KEYWORDS: Image registration, Ultrasonography, Prostate, Biopsy, Calibration, Image fusion, 3D image processing, Computed tomography, Optical tracking, Image restoration, Positron emission tomography, Magnetic resonance imaging, Imaging systems

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Proceedings Article | 21 March 2016 Paper

Deformable image registration with a featurelet algorithm: implementation as a 3D-slicer extension and validation

A. Renner, H. Furtado, Y. Seppenwoolde, W. Birkfellner, D. Georg

Proceedings Volume 9784, 97844B (2016) https://doi.org/10.1117/12.2216863

KEYWORDS: Image registration, 3D image processing, Radiotherapy, Human-machine interfaces, Computed tomography, Optical inspection, Open source software, 3D applications, Logic, Visualization, Rigid registration, Algorithm development, Tumors, Rectum, Bladder

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Proceedings Article | 21 March 2016 Paper

FIRE: an open-software suite for real-time 2D/3D image registration for image guided radiotherapy research

H. Furtado, C. Gendrin, J. Spoerk, E. Steiner, T. Underwood, T. Kuenzler, D. Georg, W. Birkfellner

Proceedings Volume 9784, 978449 (2016) https://doi.org/10.1117/12.2216082

KEYWORDS: Image registration, Radiotherapy, Software development, Lung, Motion estimation, Visualization, Medical imaging, Image processing, Tumors, X-rays, X-ray imaging

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Proceedings Article | 21 March 2014 Paper

Real-time intensity based 2D/3D registration using kV-MV image pairs for tumor motion tracking in image guided radiotherapy

H. Furtado, E. Steiner, M. Stock, D. Georg, W. Birkfellner

Proceedings Volume 9034, 90340H (2014) https://doi.org/10.1117/12.2036135

KEYWORDS: Image registration, Tumors, X-rays, X-ray imaging, Content addressable memory, Radiotherapy, Image restoration, Lung, Image processing, X-ray computed tomography

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Proceedings Article | 12 March 2014 Paper

SPECT-US image fusion and clinical applications

Johann Hummel, Marcus Kaar, Rainer Hoffmann, Wolfgang Birkfellner, Thomas Beyer, Anton Staudenherz, Michael Figl

Proceedings Volume 9036, 90362D (2014) https://doi.org/10.1117/12.2043558

KEYWORDS: Single photon emission computed tomography, Image fusion, Image registration, Calibration, Optical tracking, 3D image processing, Ultrasonography, Image segmentation, Computed tomography, Liver

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Proceedings Article | 15 March 2013 Paper

Evaluation of three 3D US calibration methods

Johann Hummel, Marcus Kaar, Rainer Hoffmann, Amon Bhatia, Wolfgang Birkfellner, Michael Figl

Proceedings Volume 8671, 86712I (2013) https://doi.org/10.1117/12.2007365

KEYWORDS: Calibration, Image registration, Optical spheres, Ultrasonography, Fermium, Frequency modulation, 3D image processing, 3D acquisition, 3D modeling, Optical tracking

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Proceedings Article | 8 March 2013 Paper

Image guidance system for flexible endoscopes considering tissue deformation

Rainer Hoffmann, Michael Figl, Amar Bhatia, Marcus Kaar, Wolfgang Birkfellner, Andreas Püspök, Alfred Kratochwil, Johann Hummel

Proceedings Volume 8671, 867104 (2013) https://doi.org/10.1117/12.2007410

KEYWORDS: Computed tomography, Image registration, 3D image processing, Calibration, Endoscopy, Optical tracking, Image fusion, 3D acquisition, Tissues, Endoscopes

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Proceedings Article | 24 February 2012 Paper

Automatic analysis of ciliary beat frequency using optical flow

Michael Figl, Manuel Lechner, Tobias Werther, Fritz Horak, Johann Hummel, Wolfgang Birkfellner

Proceedings Volume 8314, 831453 (2012) https://doi.org/10.1117/12.911616

KEYWORDS: Video, Optical flow, Fourier transforms, Motion detection, Radiation oncology, Corner detection, MATLAB, Medicine, Particles, Biological research

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Proceedings Article | 17 February 2012 Paper

Automatic patient alignment for prostate radiation applying 3D ultrasound

Marcus Kaar, Alfred Kratochwil, Michael Figl, Rainer Hoffmann, Amon Bhatia, Amar Bhatia, Wolfgang Birkfellner, Johann Hummel

Proceedings Volume 8316, 83161Q (2012) https://doi.org/10.1117/12.911038

KEYWORDS: Image registration, Computed tomography, Prostate, Image filtering, Ultrasonography, Radiotherapy, Calibration, 3D image processing, Image processing, Laser systems engineering

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Proceedings Article | 14 February 2012 Paper

Real-time 2D/3D registration for tumor motion tracking during radiotherapy

H. Furtado, C. Gendrin, C. Bloch, J. Spoerk, S. Pawiro, C. Weber, M. Figl, M. Stock, D. Georg, H. Bergmann, W. Birkfellner

Proceedings Volume 8314, 831407 (2012) https://doi.org/10.1117/12.910117

KEYWORDS: Tumors, X-rays, Image registration, Lung, X-ray imaging, Radiotherapy, Lawrencium, Motion measurement, Image processing, X-ray computed tomography

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Proceedings Article | 3 March 2011 Paper

Streak artefact quantification for abdominal CT

Michael Figl, Romana Fragner, Patrick Heimel, Christian Loewe, Wolfgang Birkfellner

Proceedings Volume 7966, 79661Q (2011) https://doi.org/10.1117/12.878577

KEYWORDS: Computed tomography, Linear filtering, Radon transform, Image processing, Image filtering, Signal attenuation, Image quality, MATLAB, Image enhancement, Radiology

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Proceedings Article | 2 March 2011 Paper

Comparison of two navigation system designs for flexible endoscopes using abdominal 3D ultrasound

Marcus Kaar, Rainer Hoffmann, Helmar Bergmann, Michael Figl, Christoph Bloch, Alfred Kratochwil, Wolfgang Birkfellner, Johann Hummel

Proceedings Volume 7964, 796418 (2011) https://doi.org/10.1117/12.878056

KEYWORDS: Image registration, Computed tomography, 3D image processing, Calibration, Optical tracking, Ultrasonography, Navigation systems, Endoscopes, Endoscopy, 3D acquisition

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Proceedings Article | 24 February 2010 Paper

Correction of prostate misalignment in radiation therapy using US-CT registration

Rainer Hoffmann, Michael Figl, Marcus Kaar, Amon Bhatia, Amar Bhatia, Wolfgang Birkfellner, Johann Hummel

Proceedings Volume 7625, 76252B (2010) https://doi.org/10.1117/12.844269

KEYWORDS: Prostate, Image registration, Computed tomography, Radiotherapy, Bladder, Calibration, Tissues, X-ray computed tomography, Rectum, Optical tracking

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Latest developments in radiation therapy such as IGRT (image guided radiation therapy) and IMRT (intensity modulated radiation therapy) promise to spare organs at risk by applying better dose distribution on the tumor. For any effective application of these methods the exact positioning of the patient and the localization of the exposured organ is crucially. With respect to the filling of rectum and bladder the prostate can move several millimeters up to centimeters. That implies the need of daily determination and correction of the position of the prostate before irradiation. We calibrated a scan head of a B-mode US machine (Ultramark 9, advanced Technology Laboratories, USA) by means of an optical tracking system (Polaris, NDI, Can). 2D/3D registration was accomplished by minimizing an adapted mutual information function. Before the registration procedure was started CT respectively US images were preprocessed by applying various filters and masks. For registration between the tracking system and the coordinate system of the Linac (defined by the positioning laser system) a block with three drilled holes was used. Since the coordinates of the holes are known in both coordinate systems a simple point-to-point registration fulfills the task. The complete system setup was evaluated by means of a water-filled balloon embedded in a gelatinetank. For additional evaluation of the 2D/3D registration we used real patient data. For evaluation of the 2D/3D registration on patient data the prostate was drawn in by a physician on the US image and the reformatted CT slice. Then, the Hausdorff distance between the two structures was calculated. The target registration error (TRE) with respect to the balloon experiments amounted to be 2.1mm±1.2mm for 10 targets. The US calibration was accomplished with an error of 0.8mm± 0.2mm (five calibrations). With respect to the 2D/3D registration we found an Hausdorff distance of 2.6mm. The results imply that the method is sufficiently accurate and robust. It can be easily applied to older linear accelerators at low costs.

Proceedings Article | 24 February 2010 Paper

Towards real-time 2D/3D registration for organ motion monitoring in image-guided radiation therapy

C. Gendrin, J. Spoerk, C. Bloch, S. A. Pawiro, C. Weber, M. Figl, P. Markelj, F. Pernus, D. Georg, H. Bergmann, W. Birkfellner

Proceedings Volume 7625, 762512 (2010) https://doi.org/10.1117/12.844201

KEYWORDS: Image registration, X-rays, X-ray imaging, Volume rendering, Tumors, X-ray computed tomography, Radiotherapy, Chromium, Imaging systems, Gold

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Proceedings Article | 24 February 2010 Paper

Measurement of complex joint trajectories using slice-to-volume 2D/3D registration and cine MR

C. Bloch, M. Figl, C. Gendrin, C. Weber, E. Unger, S. Aldrian, W. Birkfellner

Proceedings Volume 7625, 76253C (2010) https://doi.org/10.1117/12.844109

KEYWORDS: Image registration, Image segmentation, Magnetic resonance imaging, Image fusion, Medical imaging, Visualization, Visual process modeling, Current controlled current source, In vivo imaging, Kinematics

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Proceedings Article | 24 February 2010 Paper

A comment on the rank correlation merit function for 2D/3D registration

Michael Figl, Christoph Bloch, Wolfgang Birkfellner

Proceedings Volume 7625, 76251W (2010) https://doi.org/10.1117/12.845660

KEYWORDS: Image registration, 3D image processing, Medical imaging, Stochastic processes, Correlation function, Ultrasonography, Statistical analysis, Biomedical engineering, Physics, Data centers

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Proceedings Article | 24 February 2010 Paper

A new gold-standard dataset for 2D/3D image registration evaluation

Supriyanto Pawiro, Primoz Markelj, Christelle Gendrin, Michael Figl, Markus Stock, Christoph Bloch, Christoph Weber, Ewald Unger, Iris Nöbauer, Franz Kainberger, Helga Bergmeister, Dietmar Georg, Helmar Bergmann, Wolfgang Birkfellner

Proceedings Volume 7625, 76251V (2010) https://doi.org/10.1117/12.844488

KEYWORDS: Image registration, X-ray imaging, X-rays, Gold, 3D image processing, Magnetic resonance imaging, 3D image reconstruction, X-ray computed tomography, Imaging systems, Radiotherapy

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Proceedings Article | 13 March 2009 Paper

Evaluation of dynamic electromagnetic tracking deviation

Johann Hummel, Michael Figl, Michael Bax, Ramin Shahidi, Helmar Bergmann, Wolfgang Birkfellner

Proceedings Volume 7261, 72612U (2009) https://doi.org/10.1117/12.813645

KEYWORDS: Sensors, Electromagnetism, Metals, Data analysis, Error analysis, Navigation systems, Data acquisition, Optical spheres, Medical imaging, Motion measurement

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Proceedings Article | 22 March 2007 Paper

Motion correction for radiation therapy of the prostate using B-mode ultrasound

Johann Hummel, Michael Figl, Jörg Schmidbauer, Martina Tinzl, Helmar Bergmann, Wolfgang Birkfellner

Proceedings Volume 6509, 65092F (2007) https://doi.org/10.1117/12.708190

KEYWORDS: Image registration, Prostate, Calibration, Ultrasonography, Radiotherapy, Computed tomography, Optical tracking, Modulation, Tumors, Optical calibration

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The use of intensity modulated radiation therapy promises to spare organs at risk by applying better dose distribution on the tumor. The specific challenge of this methods is the exact positioning of the patient and the localization of the exposured organ. With respect to the filling of rectum and bladder the prostate can move several millimeters up to centimeters. Therefore, the position of the prostate should be determinated and corrected daily before irradiation. We used a B-mode US machine (Ultramark 9, advanced Technology Laboratories, USA) which was calibrated using an optical tracking system (Polaris, NDI, Can). After correct positioning of the patient in the simulation room three anatomical markers (apex prostate, prostate lateral sinister/dexter) were identified and their positions calculated with respect to the coordinate system of the simulator. The same situation is given in the treatment room. Both, simulator and accelerator are registered by a simple point-to-point registration using a block with five drilled holes with known coordinates in the block coordinate system. The block is aligned by means of laser markers. When the patient is placed on the treatment table, the three anatomical landmarks are located on the US images and their positions are calculated with respect to the coordinate system of the treatment room. Applying a point-to-point registration results in a rotation matrix and a translation vector in the desired coordinate system which can be used for repositioning by translating and rotating the patient table. Additionally, a fiducial registration error (FRE) is calculated which gives a dimension of the accuracy the three points were identified. We found an fiducial registration error (FRE) of 2.4 mm +/- 1.2 mm for the point-to-point registration of the anatomical landmarks. The FRE for the point-to-point registration between the block and the optical tracking system was 0.5 mm +/- 0.2 mm. According to the US calibration we found an error of 0.8 mm +/- 0.2 mm.

Proceedings Article | 22 March 2007 Paper

Stochastic rank correlation for slice-to-volume registration of fluoroCT/CT imaging

Wolfgang Birkfellner, Michael Figl, Helmar Bergmann

Proceedings Volume 6509, 650937 (2007) https://doi.org/10.1117/12.711394

KEYWORDS: Image registration, Stochastic processes, Medical imaging, Digital imaging, X-ray computed tomography, Magnetic resonance imaging, Computed tomography, Optimization (mathematics), Image restoration, Image processing

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Proceedings Article | 13 March 2006 Paper

Endoscopic navigation system using 2D/3D registration

Johann Hummel, Michael Figl, Helmar Bergmann, Wolfgang Birkfellner

Proceedings Volume 6141, 614114 (2006) https://doi.org/10.1117/12.654337

KEYWORDS: Calibration, Computed tomography, Image registration, Endoscopes, Endoscopy, Navigation systems, Ultrasonography, Image fusion, Head, Video

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Proceedings Article | 12 April 2005 Paper

Design and automatic calibration of a head mounted operating binocular for augmented reality applications in computer-aided surgery

Michael Figl, Christopher Ede, Wolfgang Birkfellner, Johann Hummel, Rudolf Hanel, Helmar Bergmann

Proceedings Volume 5744, (2005) https://doi.org/10.1117/12.595161

KEYWORDS: Calibration, Head-mounted displays, Autoregressive models, Zoom lenses, Cameras, Surgery, Human-machine interfaces, Head, Augmented reality, Detection and tracking algorithms

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Proceedings Article | 12 April 2005 Paper

Standardized evaluation method for electromagnetic tracking systems

Johann Hummel, Calvin Maurer, Michael Figl, Michael Bax, Helmar Bergmann, Wolfgang Birkfellner, Ramin Shahidi

Proceedings Volume 5744, (2005) https://doi.org/10.1117/12.595256

KEYWORDS: Sensors, Electromagnetism, Distortion, Magnetism, Aluminum, Optical sensors, Endoscopes, Optical tracking, Auroras, Calibration

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Proceedings Article | 12 May 2004 Paper

2D/3D registration using a rotation-invariant cost function based on Zernike moments

Wolfgang Birkfellner, Xinhui Yang, Wolfgang Burgstaller, Bernard Baumann, Augustinus Jacob, Peter Niederer, Pietro Regazzoni, Peter Messmer

Proceedings Volume 5370, (2004) https://doi.org/10.1117/12.531976

KEYWORDS: Image registration, X-rays, X-ray imaging, Image processing, Image resolution, Surgery, X-ray computed tomography, Calibration, Medical imaging, Bone

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Proceedings Article | 5 May 2004 Paper

Hybrid tracking system for flexible endoscopes

Johann Hummel, Michael Figl, Wolfgang Birkfellner, Christopher Ede, Rudolf Seemann, Helmar Bergmann

Proceedings Volume 5367, (2004) https://doi.org/10.1117/12.534002

KEYWORDS: Sensors, Calibration, Endoscopes, Image registration, Head, Ultrasonography, Computed tomography, Optical spheres, Electromagnetism, Optical tracking

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Proceedings Article | 5 May 2004 Paper

Automatic calibration of an optical see-through head-mounted display for augmented reality applications in computer assisted interventions

Michael Figl, Christopher Ede, Wolfgang Birkfellner, Johann Hummel, Rudolf Seemann, Helmar Bergmann

Proceedings Volume 5367, (2004) https://doi.org/10.1117/12.534020

KEYWORDS: Calibration, Zoom lenses, Head-mounted displays, Cameras, Image segmentation, Head, CCD cameras, Surgery, Imaging systems, Augmented reality

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Proceedings Article | 30 May 2003 Paper

Navigation system for flexible endoscopes

Johann Hummel, Michael Figl, Wolfgang Birkfellner, Michael Häfner, Christian Kollmann, Helmar Bergmann

Proceedings Volume 5029, (2003) https://doi.org/10.1117/12.479837

KEYWORDS: Optical spheres, Calibration, Ultrasonography, Computed tomography, Endoscopes, Sensors, Image registration, Head, Navigation systems, Magnetic resonance imaging

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Endoscopic Ultrasound (EUS) features flexible endoscopes equipped with a radial or linear array scanhead allowing high resolution examination of organs adjacent to the upper gastrointestinal tract. An optical system based on fibre-glass or a CCD-chip allows additional orientation. However, 3-dimensional orientation and correct identification of the various anatomical structures may be difficult. It therefore seems desirable to merge real-time US images with high resolution CT or MR images acquired prior to EUS to simplify navigation during the intervention. The additional information provided by CT or MR images might facilitate diagnosis of tumors and, ultimately, guided puncture of suspicious lesions. We built a grid with 15 plastic spheres and measured their positions relatively to five fiducial markers placed on the top of the grid. For this measurement we used an optical tracking system (OTS) (Polaris, NDI, Can). Two sensors of an electromagnetic tracking system (EMTS) (Aurora, NDI, Can) were mounted on a flexible endoscope (Pentax GG 38 UX, USA) to enable a free hand ultrasound calibration. To determine the position of the plastic spheres in the emitter coordinate system of the EMTS we applied a point-to-point registration (Horn) using the coordinates of the fiducial markers in both coordinate systems (OTS and EMTS). For the transformation between EMTS to the CT space the Horn algorithm was adopted again using the fiducial markers. Visualization was enabled by the use of the AVW-4.0 library (Biomedical Imaging Resource, Mayo Clinic, Rochester/MN, USA). To evaluate the suitability of our new navigation system we measured the Fiducial Registration Error (FRE) of the diverse registrations and the Target Registration Error (TRE) for the complete transformation from the US space to the CT space. The FRE for the ultrasound calibration amounted to 4.3 mm ± 4.2 mm, resulting from 10 calibration procedures. For the transformation from the OTS reference system to the EMTS emitter space we found an average FRE of 0.8 mm ± 0.2 mm. The FRE for the CT registration was 1.0 mm ± 0.3 mm. The TRE was found to be 3.8 mm ± 1.3 mm if we target the same spheres which where used for the calibration procedure. A movement of the phantom results in higher TREs because of the orientation sensitivity of the sensor. In that case the TRE in the area where the biopsy is supposed to be taken place was found to be 7.9 mm ± 3.2 mm. Our system provides the interventionist with additional information about position and orientation of the used flexible instrument. Additionally, it improves the marksmanship of biopsies. The use of the miniaturized EMTS enables for the first time the navigation of flexible instruments in this way. For the successful application of navigation systems in interventional radiology, an accuracy in the range of 5 mm is desirable. The accuracy of the localization of a point in CT space are just 3 mm too high as required. One of the possibilities to overcome this difference is to mount the two sensors in such a way that the interference of their electromagnetic fields is minimized. A considerable restraint constitutes the small characteristic volume (360mm x 600mm x 600mm), which requires for most application an additional optical system.

Proceedings Article | 30 May 2003 Paper

LORENZ: a system for planning long-bone fracture reduction

Wolfgang Birkfellner, Wolfgang Burgstaller, Joachim Wirth, Bernard Baumann, Augustinus Jacob, Kurt Bieri, Stefan Traud, Michael Strub, Pietro Regazzoni, Peter Messmer

Proceedings Volume 5029, (2003) https://doi.org/10.1117/12.479580

KEYWORDS: Bone, X-rays, Radiography, Surgery, X-ray imaging, Visualization, X-ray computed tomography, OpenGL, 3D image processing, Computed tomography

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Long bone fractures belong to the most common injuries encountered in clinical routine trauma surgery. Preoperative assessment and decision making is usually based on standard 2D radiographs of the injured limb. Taking into account that a 3D - imaging modality such as computed tomography (CT) is not used for diagnosis in clinical routine, we have designed LORENZ, a fracture reduction planning tool based on such standard radiographs. Taking into account the considerable success of so-called image free navigation systems for total knee replacement in orthopaedic surgery, we assume that a similar tool for long bone fracture reposition should have considerable impact on computer-aided trauma surgery in a standard clinical routine setup. The case for long bone fracture reduction is, however, somewhat more complicated since not only scale independent angles indicating biomechanical measures such as varus and valgus are involved. Reduction path planning requires that the individual anatomy and the classification of the fracture is taken into account. In this paper, we present the basic ideas of this planning tool, it's current state, and the methodology chosen. LORENZ takes one or more conventional radiographs of the broken limb as input data. In addition, one or more x-rays of the opposite healthy bone are taken and mirrored if necessary. A most adequate CT model is being selected from a database; currently, this is achieved by using a scale space approach on the digitized x-ray images and comparing standard perspective renderings to these x-rays. After finding a CT-volume with a similar bone, a triangulated surface model is generated, and the surgeon can break the bone and arrange the fragments in 3D according to the x-ray images of the broken bone. Common osteosynthesis plates and implants can be loaded from CAD-datasets and are visualized as well. In addition, LORENZ renders virtual x-ray views of the fracture reduction process. The hybrid surface/voxel rendering engine of LORENZ also features full collision detection of fragments and implants by using the RAPID collision detection library. The reduction path is saved, and a TCP/IP interface to a robot for executing the reduction was added. LORENZ is platform independent and was programmed using Qt, AVW and OpenGL. We present a prototype for computer-aided fracture reduction planning based on standard radiographs. First test on clinical CT-Xray image pairs showed good performance; a current effort focuses on improving the speed of model retrieval by using orthonormal image moment decomposition, and on clinical evaluation for both training and surgical planning purposes. Furthermore, user-interface aspects are currently under evaluation and will be discussed.

Proceedings Article | 30 May 2003 Paper

Rotation invariance principles in 2D/3D registration

Wolfgang Birkfellner, Joachim Wirth, Wolfgang Burgstaller, Bernard Baumann, Harald Staedele, Beat Hammer, Niels Gellrich, Augustinus Jacob, Pietro Regazzoni, Peter Messmer

Proceedings Volume 5029, (2003) https://doi.org/10.1117/12.482406

KEYWORDS: Image registration, X-rays, X-ray imaging, Surgery, X-ray computed tomography, Image resolution, Calibration, Volume rendering, Tomography, Optimization (mathematics)

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Proceedings Article | 30 May 2003 Paper

Calibration of an optical see-through head-mounted display with variable zoom and focus for applications in computer-assisted interventions

Michael Figl, Wolfgang Birkfellner, Johann Hummel, Christopher Ede, Rudolf Hanel, Helmar Bergmann

Proceedings Volume 5029, (2003) https://doi.org/10.1117/12.480211

KEYWORDS: Calibration, Zoom lenses, Head-mounted displays, Cameras, Head, Surgery, Imaging systems, Optical tracking, Microscopes, Optical calibration

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During the last few years head mounted displays (HMD) became more important in Computer assisted surgery (CAS). Rapid head movements of the surgeon enforce to change the focal plane and the zoom value without loosing the calibration. Starting from previous work in developing an optical see through head mounted display we adapted our HMD to measure the focal and zoom values. This made it possible to extend the calibration to different zoom and focus values. The case of the HMD was opened to gain access to the zoom lenses, which was necessary to measure the different zoom values. Focusing in our HMD is realized by changing the angle between the two tubes. Therefore we marked two points at the tubes to measure the focal adjustment. We made a series of planar calibrations with seven different fixed zoom and focus values using Tsai´s algorithm for camera calibration. Then we used the Polaris optical tracking system (Northern Digital, Ontario, Can) to measure the transformation from the planar calibration grid to a tracker probe rigidly mounted to the HMD. The calibration parameters transformed to this tracker probe are independent of the actual position of the calibration grid andare the parameters we want to approximate. Then least square approximating polynomial surfaces were derived for the seven calibration parameters. The coefficients of the polynomial surfaces were used as starting values for a nonlinear optimization procedure minimizing an overall error. Minimizing the object space error (which is the minimal distance of the line through the center of projection and the image point to the real world point) in the last step of the procedure described above we had a mean object space error 0.85 ±0.5 mm. Calibration of the HMD is not lost during minor changes in zoom and focus. This is likely to be the first optical see through HMD developed for CAS with variable zoom and focus, which are typically facilities of operating microscopes. Employing an automated calibration in common with more zoom and focus steps and more accurate measurement of the position of the zoom lenses and the focal plane should reduce the error significantly, enabling the accuracy needed for CAS.

Proceedings Article | 17 May 2002 Paper

Laboratory assessment of a miniature electromagnetic tracker

Johann Hummel, Wolfgang Birkfellner, Michael Figl, C. Haider, Rudolf Hanel, Helmar Bergmann

Proceedings Volume 4681, (2002) https://doi.org/10.1117/12.466909

KEYWORDS: Sensors, Head, Optical tracking, Electromagnetism, Fluoroscopy, Navigation systems, Reliability, Image intensifiers, Endoscopes, Data acquisition

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With the invention of miniaturized electromagnetic digitizers comes a variety of potential clinical applications for computer aided interventions using flexible instruments; it has become possible to track endoscopes or catheters within the body. To evaluate the reliability of a new commercial tracking system, we measured the systematic distortions induced by various materials such as closed metallic loops, wire guides, catheters and ultrasound scan heads. The system under evaluation was the electromagnetic tracking system Aurora (Mednetix/CH, NDI/Can); data were acquired using the serial port of a PC running SuSE Linux 7.1 (SuSE, Gmbh, Nuernberg). The objects suspected to cause distortions were brought into the digitizer volume. Beside this, we evaluated the influence of a C-arm fluoroscopy unit. To quantify the reliability of the system, the miniaturized sensor was mounted on a nonmetallic measurement rack while the transmitter was fixed at three different distances within the digitizer range. The tracker is more sensitive to distortions caused by materials close to the emitter (average value 13.6 mm +/- 16.6mm) for wire loops positioned at a distance between 100 mm and 200 mm from the emitter). Distortions caused by materials near the sensor (distances smaller than 100 mm) are small (typical error: 2.2 mm +/- 1.9 mm) in comparison to the errors of other electromagnetic systems published in an earlier study of our group where we found an average error of 3.4 mm. Considerable distortions are caused by the C-arm fluoroscopy unit and limits the reliability of the tracker (error: 18.6 mm +/- 24.9 mm). The US scan head was found to cause significant distortions only at a distance between the emitter and the scan head less than 100 mm from the emitter in contrast to the average error of 3.8 mm +/- 6.3 mm at distances greater than 100 mm. Taking into account that significant distortions only occur in the presence of metallic objects close to the emitter, these results indicate the opportunities which are now available in surgical applications where flexible instruments may need to be monitored within the patient.

Proceedings Article | 17 May 2002 Paper

Stereoscopic visualization in the varioscope AR: a see-through head-mounted display for surgical navigation

Wolfgang Birkfellner, Michael Figl, Christian Matula, Johann Hummel, Rudolf Hanel, Herwig Imhof, Felix Wanschitz, Arne Wagner, Franz Watzinger, Helmar Bergmann

Proceedings Volume 4681, (2002) https://doi.org/10.1117/12.466947

KEYWORDS: Head-mounted displays, Optical spheres, Visualization, Navigation systems, Surgery, Skull, Computer graphics, Optical tracking, Head, Computed tomography

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Proceedings Article | 17 May 2002 Paper

PC-based control unit for a head-mounted operating microscope for augmented-reality visualization in surgical navigation

Michael Figl, Wolfgang Birkfellner, Franz Watzinger, Felix Wanschitz, Johann Hummel, Rudolf Hanel, Rolf Ewers, Helmar Bergmann

Proceedings Volume 4681, (2002) https://doi.org/10.1117/12.466983

KEYWORDS: Head-mounted displays, Visualization, Control systems, Telecommunications, Microscopes, Calibration, Computer graphics, Light emitting diodes, Head, Surgery

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Proceedings Article | 28 May 2001 Paper

Calibration of projection parameters in the varioscope AR, a head-mounted display for augmented-reality visualization in image-guided therapy

Wolfgang Birkfellner, Michael Figl, Klaus Huber, Johann Hummel, Rudolf Hanel, Peter Homolka, Franz Watzinger, Felix Wanschitz, Rolf Ewers, Helmar Bergmann

Proceedings Volume 4319, (2001) https://doi.org/10.1117/12.428089

KEYWORDS: Head-mounted displays, Calibration, Visualization, Distortion, Zoom lenses, Microscopes, Optical tracking, 3D displays, Surgery, Navigation systems

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Proceedings Article | 18 April 2000 Paper

Computer-aided insertion of endosteal implants in the zygoma: a pilot study

Wolfgang Birkfellner, Franz Watzinger, Felix Wanschitz, F. Ziya, J. Kremser, A. Potyka, R. Mayr, Klaus Huber, F. Kainberger, Rolf Ewers, Helmar Bergmann

Proceedings Volume 3976, (2000) https://doi.org/10.1117/12.383048

KEYWORDS: Bone, Computed tomography, Surgery, Visualization, Optical tracking, Light emitting diodes, Head, Software development, Skull, Navigation systems

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Showing 5 of 37 publications

Conference Committee Involvement (18)