Virtual bronchoscopy for three--dimensional pulmonary image assessment: state of the art and future needs

Virtual bronchoscopy is emerging as a useful approach for assessment of three-dimensional (3D) computed tomographic (CT) pulmonary images. A protocol for virtual bronchoscopic assessment of a 3D CT pulmonary image would have two main stages: (a) preprocessing of image data, which involves extracting objects of interest, defining paths through major airways, and preparing the extracted objects for 3D rendering; and (b) interactive image assessment, which involves use of graphics-based software tools such as surface-rendered views, projection images, virtual endoscopic views, tube views, oblique section images, measurement data, global two-dimensional section images, and cross-sectional views. Although a virtual bronchoscope offers a unique opportunity for exploration and quantitation, it cannot replace a real bronchoscope. Limitations of current virtual endoscopy systems include high cost, lack of visual aids beyond simulated endoscopic views, difficulty in performing interactive anatomic exploration, lack of quantitative information, use of surface rendering instead of volume rendering, and need for substantial off-line display computation. Future needs include development of fully integrated user-friendly virtual bronchoscopes, development of optimal CT protocols for generating artifact-free data sets, and improvements in automated preprocessing of 3D CT images.