Virtual Bronchoscopy, Colonoscopy, IVU
In the clinical evaluation of pulmonary disease, fiberoptic bronchosopy is a crucial tool in the diagnosis of a variety of chest diseases. Though often instrumental in the diagnosis of a variety of neoplastic, inflammatory, and infectious diseases, fiberoptic bronchscopy (FOB) can have important limitations: it is invasive and time-consuming, and it requires sedation. It may not be tolerated in the young, in the critically ill, or in patients with coagulopathies. In patients with significant airway disease/stenoses, bronchoscopic evaluation of the airway distal to areas of stenoses/narrowing is technically difficult and may compromise patient oxygenation significantly. Equally important, the evaluation of extraluminal pathology is significantly limited in fiberoptic bronchoscopy.
The effective use of VB necessitates an understanding of the anatomy seen during fiberoptic bronchoscopy. In particular, the perspective of the bronchoscopist is opposite the traditional orientation of the radiologist: the bronchoscope displays airway anatomy in a cranial-caudal direction, with the patient in a supine position (Figure 1). For radiologists involved with VB, a solid understanding of this anatomic perspective is important, and active participation/correlation with fiberoptic bronchoscopy is helpful in understanding the capabilities and limitations of VB. In most VB software packages, both surface and volume rendering can be performed. Surface rendering has been used routinely because reconstruction times are considerately faster than volume rendering techniques. Standard threshold values for surface-rendering techniques have been described.While these thresholds are effective in the main and lobar bronchi, artifacts can occur in the smaller airways, and may also result in an overestimation of stenosis. Currently, faster computer reconstruction times and more flexible thresholding capabilities have made volume-rendered VB our technique of choice in the evaluation of the airway.