Patients with diseases of the air passages who are enrolled in an NIH clinical trial may participate in this study, which requires having a CT scan. The patient lies on a table that slowly slides into a hole in a donut-shaped X-ray machine (the scanner). Patients may have to hold their breath several times during the procedure. Some patients may be given an injection of a contrast agent through a catheter (thin tube) placed in an arm vein to improve visibility of abnormalities. Patients may also be asked to breathe oxygen through nasal prongs to allow them to hold their breath longer. The procedure usually takes 15 to 20 minutes.