It has been reported that axial CT is as accurate as fiberoptic bronchoscopy (FOB) for evaluation of central airways, with the exception of very small mucosal abnormalities (< 3 mm), subtle mucosal and submucosal irregularities, and infection. Compared to FOB, an axial CT can evaluate both intraluminal and extraluminal disease.
Helical CT has improved the evaluation of central airways by virtually eliminating slice misregistration and respiratory motion artifacts. By obtaining a continuous volume data set during a single breath-hold, two-dimensional reformatted images and 3D reconstructions can be generated utilizing a variety of reconstruction/rendering techniques. In some circumstances, such as the evaluation of stenoses in obliquely oriented bronchi, these reconstructions may substantially improve the diagnostic accuracy or facilitate the interpretation of anatomy.
So-called virtual bronchoscopy (VB), or CT bronchography, has received considerable attention in the recent literature. Excellent internal images of the tracheobronchial tree can be generated to the level of the 4th or 5th generation bronchi. 3D reconstructions can be viewed from either an external or an internal perspective (Fig 7, 8). birth control pills
Proposed uses of VB include screening airways for endoluminal malignancy, evaluating airway stenoses, and using it as a “road map” for FOB. Experience thus far suggests that VB probably does not accurately detect and define small mucosal and submucosal lesions. On the other hand, several studies document that VB accurately detects and quantifies airway stenoses when compared to FOB, which may be important in stent planning. VB is probably slightly more accurate than axial thin-section CT scans for the evaluation of stenoses. However, the role of VB (if any) in the evaluation of airway stenoses remains controversial. VB may eventually prove most useful as an adjunct to FOB, perhaps as a means of following known stenoses after therapy or in patients who cannot tolerate FOB. It may be useful also in patients with stenoses that are too narrow for the FOB device to pass through (since the airway distal to the narrowing can be visualized and the “VB scope” can be turned retrograde to look at the airway).
In a preliminary investigation, McAdams et al found that VB was useful for directing transbronchial needle aspiration in patients with enlarged nodes. The potential applications of VB are numerous, although the technology remains, as yet, in its infancy. Only time will tell what, if any, important role VB plays in clinical practice.
Figure 7. Virtual bronchoscopy. Axial CT image shows high-density object (arrow) representing an aspirated dental bridge in left bronchus
Figure 8. Top: volume-rendered CT image from VB showing endoluminal view of the foreign body (white area is dental bridge). Bottom: corresponding video image from actual bronchoscopy. (Courtesy of Bernard A. Birnbaum, MD, University of Pennsylvania Medical Center.)