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Medical Volume Rendering

Background: 
This research field is about several aspects of rendering medical volume data:
  • Augmented Reality for Guided Surgery
Augmented reality systems (ARS) compine the physicians real view onto the patient with semi-transparent computer-generated images of preoperatively acquired CT data. The challenge is to compensate the motion of the patient and non-linear tissue deformation during the intervention. The framework of our Augmented Reality System is a texture-based volume rendering component on commodity PC hardware which allows interactive volumetric deformation based on piecewise linear transformations. The volume is adaptively subdivided into a hierarchy of hexahedra, each of which is deformed linearly. The registration is implemented as a two-stage procedure. First, we compute a rigid pre-registration with respect to the external fiducial markers in combination with an electro-magnetic tracking system. In the second step, the non-linear part of the transformation is determined by using an analysis-by-synthesis approach. Several views onto the real object are captured and compared with the corresponding synthetic renderings. Mutual information is used as similarity metric.
  • Repositioning of Bone Fractures
The goal of this project was the development of an easy-to-use application for semi-automatic repositioning of bone fractures which allows several fragments to be merged. This application has been developed with regard to orthopaedic surgeons who want to simulate the position and orientation of bone fragments preoperatively. The interactive algorithm includes volumetric collision detection for intuitive navigation and coarse manual positioning. Additionally, an optimization process for the mathematically exact repositioning of the bone fragments is implemented. In order to accelerate the volumetric collision detection, octree structures are used that are efficiently implemented as an hierarchy of oriented bounding boxes (OBB). The collision test uses the separating axis theorem for a fast traversal of the octree. To improve the manual part of the repositioning process, the principal axes of each fragment are precalculated initially. Subsequently, the fragments are pre-justified by the user. Finally, an optimization process is performed based on Powell's algorithm for multidimensional minimization. The optimal position of the bone fragments is determined by the use of a voxel-based metric, that exploits the same bounding box hierarchy.
  • Visualization of Spine Data Sets from MR
Degenerative discogenic diseases of the vertebral column are mainly caused by malformation or dislocation of the intervertebral discs and deformations of the spinal cord. Slipped or ruptured disks can cause severe spinal stenosis, narrowing of the spinal canal and a resulting constriction of the nerves. In the same context the term spondylolisthesis refers to a forward displacement of a lumbar vertebra on the sacrum which again produces a compression of nerve roots. For the diagnosis and the therapy planning of intervertebral disk diseases detailed information of the relevant structures and their spatial relations is required. In clinical practise, the traditional method to examine complex cases of extreme spinal stenosis and herniated intervertebral disks requires the injection of contrast dye into the spinal subarachnoid space (x-ray myelography). This is an invasive and time-consuming procedure that comes with a considerable risk for the patient.To these ends an alternative examination method based on an highly optimized MRI sequence was developed by Dr. Knut Eberhardt at the Division of Neuroradiology. For the visualization of the data we again propose a fast sequence of simple image-processing operations for a coarse separation of anatomical structures similar to the visualization of dural arteriovenous fistulae described in the previous chapter.
  • Semantic Models for Medical Volume Visualization
Many sophisticated techniques for the visualization of volumetric data such as medical data have been published. While existing techniques are mature from a technical point of view, managing the complexity of visual parameters is still difficult for non-expert users. To this end, we present new ideas to facilitate the specification of optical properties for direct volume rendering. We introduce an additional level of abstraction for parametric models of transfer functions. The proposed framework allows visualization experts to design high-level transfer function models which can intuitively be used by non-expert users. The results are user interfaces which provide semantic information for specialized visualization problems. The proposed method is based on principal component analysis as well as on concepts borrowed from computer animation.
Publications: 


2006

Artikel in Zeitschriften

[bib] - Christof Rezk-Salama, Maik Keller, Peter Kohlmann - High-Level User Interfaces for Transfer Function Design with Semantics
In IEEE Trans. on Visualization and Computer Graphics (Proc. IEEE Visualization), 11(5), 2006, pages 1021-1028 - [pdf]

Begutachtete Konferenzbeiträge

[bib] - Christof Rezk-Salama - Ein semantisches Modell für die Entwicklung von Softwareassistenten zur medizinischen Visualisierung
In Softwareassistenten, LNI Lecture Notes in Informatics., 2006 - [pdf]

2002

Artikel in Zeitschriften

[bib] - K. E. W. Eberhardt, B. Tomandl, C. Rezk-Salama, R. Schindler, W. Huk, M. Lell - Funktionelle hochauflösende 3D Untersuchungen der Lendenwirbelsäule mit Hilfe der Magnetresonanztomographie
In electromedica, 70(1), 2002 - [pdf]

Artikel in Zeitschriften

[bib] - K. E. W. Eberhardt, B.Tomandl, C. Rezk-Salama, R. Schindler, W. Huk, M. Lell - Functional High-Definition 3D Studies of the Lumbar Spine Using Magnetic Resonance Imaging
In electromedica, 70(1), 2002 - [pdf]

Begutachtete Konferenzbeiträge

[bib] - M. Scheuering, C- Rezk-Salama, H. Barfuss, A. Schneider, G. Greiner - Augmented Reality Based On Fast Deformable 2D-3D Registration For Image Guided Surgery
In Proc. SPIE Medical Imaging, 2002 - [pdf]

2001

Begutachtete Konferenzbeiträge

[bib] - M. Scheuering, C. Rezk-Salama, H. Barfuß, K. Barth, A. Schneider, G. Greiner, G. Wessels, G.H. Feussner - Intra-operative Augmented Reality (AR) With Magnetic Navigation and Multi-Texture Based Volume Rendering for Minimally Invasive Surgery
In Rechner- und Sensorgestützte Chirurgie, 2001 - [pdf]

Begutachtete Konferenzbeiträge

[bib] - M. Scheuering, C. Eckstein, C. Rezk-Salama, K. Hormann, G. Greiner - Interactive Repositioning of Bone Fracture Segments
In Proc. Vision Modeling and Visualization (VMV), 2001 - [pdf]

2000

Artikel in Zeitschriften

[bib] - P. Hastreiter, C. Rezk-Salama, K. Eberhardt, B. Tomandl, T. Ertl - Functional Analysis of the Vertebral Column based on MR and Direct Volume Rendering
In Proc. Medical Image Computing and Computer Assisted Intervention (MICCAI), 2000 - [pdf]