A new hybrid renderer for virtual bronchoscopy.

PURPOSE: To improve the diagnosis of pathologic modified airways, a new hybrid visualization system has been developed and tested based on digital image analysis and synthesis of spiral CT as well as the visual simulation of bronchoscopy. METHOD/MATERIALS: 20 patients with pathologic modifications of the airways (tumors, lung transplantation) were examined with Spiral-CT. The shape of the airways and the lung tissue is defined by an automatic volume growing method and a following geometric reconstruction by the computation of geometric primitives. This is the basis of a multidimensional display system which visualizes volumes, surfaces and computation results simultaneously. The enable the intuitive and immersive inspection of the airways a virtual reality system, consisting of two graphic engines, a head mounted display system, data gloves and specialized software was integrated. RESULTS: In 20 cases the extension of the pathologic modification of the airways could be visualized with the virtual bronchoscopy. The user interacts with and manipulates the 3D model of the airways in an intuitive and immersive way. In contrast to previously proposed virtual bronchoscopy systems the described method permits truly interactive navigation, detailed quantitation of anatomic structures and a "see through" the bronchial wall. The system enables a user oriented and fast inspection of the volumetric image data. CONCLUSIONS: To support radiological diagnosis with additional information a virtual bronchoscopy was developed. It enables the immersive and intuitive interaction with 3D Spiral CTs by truly 3D navigation in the airways. The system was tested with 20 Spiral-CTs of bronchial tumors and obstructions and is well suited for the inspection of structures beyond the bronchialtree.

[Computer-assisted diagnosis based on computer-based image interpretation and 3D-visualization]. / Computergestützte Diagnostik basierend auf computergestützter Bildanalyse und 3D-Visualisierungen.

PURPOSE: To survey methods for 3D data visualization and image analysis which can be used for computer based diagnostics. MATERIAL AND METHODS: The methods available are explained in short terms and links to the literature are presented. Methods which allow basic manipulation of 3D data are windowing, rotation and clipping. More complex methods for visualization of 3D data are multiplanar reformation, volume projections (MIP, semi-transparent projections) and surface projections. Methods for image analysis comprise local data transformation (e.g. filtering) and definition and application of complex models (e.g. deformable models). RESULTS: Volume projections produce an impression of the 3D data set without reducing the data amount. This supports the interpretation of the 3D data set and saves time in comparison to any investigation which requires examination of all slice images. More advanced techniques for visualization, e.g. surface projections and hybrid rendering visualize anatomical information to a very detailed extent, but both techniques require the segmentation of the structures of interest. Image analysis methods can be used to extract these structures (e.g. an organ) from the image data. DISCUSSION: At the present time volume projections are robust and fast enough to be used routinely. Surface projections can be used to visualize complex and presegmented anatomical features.

[Virtual and three-dimensional bronchoscopy with spiral and electron beam computed tomography]. / Virtuelle und dreidimensionale Bronchoskopie mit Spiral- und Elektronenstrahl-Computertomographie.

PURPOSE: To compare spiral computed tomography (CT) and electron-beam CT (EBT) for 3D and virtual CT-bronchoscopy. MATERIALS AND METHODS: 17 patients with various disorders of the tracheobronchial system were examined using fiberoptic bronchoscopy, spiral CT and EBT. 3D images were reconstructed from CT data sets using automated segmentation based on volume-growing methods. Surface-rendered, volume-rendered, and hybrid reconstructions were visualized in real time using a data helmet. RESULTS: All data sets could be processed to high-quality three-dimensional (3D) and virtual reconstructions. The reduction of motion artifacts due to shorter scan times made EBT data sets better suited for automated segmentation and less susceptible to motion artifacts. 3D and virtual reconstructions did not increase the diagnostic sensitivity of CT compared to axial reconstructions alone. CONCLUSIONS: Shorter scan times of CT imaging yield higher-quality 3D and virtual reconstructions. Modern reconstruction techniques are valuable visualization tools for select indications and are the prerequisite for future developments in computer-aided medicine.

VR interaction techniques for medical imaging applications.

Methods of virtual reality (VR) offer new ways of human-computer interaction. Medicine is predestined to benefit from this new technology in many ways. Virtual environments can support physicians in their work, alleviate communication between specialists from different fields or be established in educational and training applications. For the field of visualization and analysis of three-dimensional anatomical images (e.g. CT or MRI scans), an application is introduced which expedites recognition of spatial coherencies and the exploration and manipulation of the 3D data. To avoid long periods of learning and accustoming and to facilitate work in such an environment, a powerful human-oriented interface is required allowing interactions similar to the real world and utilization of our natural experiences. This paper shows the use of eye tracking parameters for a level-of-detail algorithm and the integration of a glove-based hand gesture recognition into the virtual environment as an essential component of the human-machine interface. Furthermore, virtual bronchoscopy and virtual angioscopy are presented as examples for the use of the virtual environment.

[Principles and current possibilities of virtual scenarios for surgery planning]. / Prinzipien und derzeitige Möglichkeiten virtueller Szenarien für die operative Therapieplanung.

This paper describes several new visualization and interaction techniques that enable the use of virtual environments for routine medical purposes. A new volume-rendering method supports shaded and transparent visualization of medical image sequences in real-time with an interactive threshold definition. Based on these rendering algorithms a segmentation approach offers intuitive assistance for a wide range of requirements in diagnosis and therapy planning. In addition, a hierarchical data representation for geometric surface descriptions guarantees optimal use of available hardware resources and prevents inaccurate visualization. Applications such as virtual endoscopy are described.

Virtual reality in medicine-computer graphics and interaction techniques.

This paper describes several new visualization and interaction techniques that enable the use of virtual environments for routine medical purposes. A new volume-rendering method supports shaded and transparent visualization of medical image sequences in real-time with an interactive threshold definition. Based on these rendering algorithms two complementary segmentation approaches offer an intuitive assistance for a wide range of requirements in diagnosis and therapy planning. In addition, a hierarchical data representation for geometric surface descriptions guarantees an optimal use of available hardware resources and prevents inaccurate visualization. The combination of the presented techniques empowers the improved human-machine interface of virtual reality to support every interactive task in medical three-dimensional (3-D) image processing, from visualization of unsegmented data volumes up to the simulation of surgical procedures.