Virtual bronchoscopy of peripheral nodules using arteries as surrogate pathways

The recent introduction of ultrathin bronchoscopy offers considerable promise for diagnosing even small peripheral lung nodules previously considered inaccessible for routine flexible bronchoscopy. However this requires obtaining an accurate roadmap prior to endoscopy. Although virtual bronchoscopy (VB) has proved to be a useful tool for planning transbronchial interventions involving the central airways, to date, VB has received little attention for providing roadmaps to peripheral lesions. This may be especially problematic, as ultrathin bronchoscopes can now access airways not visualized on routine high-resolution CT scanners. We propose to extend the reach of virtual bronchoscopy by using peripheral arteries as surrogates for peripheral bronchi that cannot be identified even with high-resolution CT technique. Since every bronchus is accompanied by an artery, it should hypothetically be possible to substitute one for another and derive useful navigational roadmaps. This paper presents a preliminary investigation of this concept, using a combination of virtual endoscopic techniques. Virtual angioscopic and bronchoscopic flythroughs are created and transition points are selected at points that can be easily identified on CT images as corresponding structures. The proximal bronchial path and the distal arterial path are then combined and presented as a single continuous flythrough. Our preliminary investigations show that as expected, the local geometry of the airway and corresponding artery are similar. In addition to visual inspection, we use the segmentation of the arterial and bronchial trees and their tree models. Selected paths from each tree model are compared by various similarity measures in order to demonstrate their correspondence. We anticipate that this technique for bronchoscopy planning will enable bronchoscopic evaluation of previously unreachable peripheral lung nodules.