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We have obtained bronchograms in living dogs and in isolated human lungs by insufflating powdered tantalum. Tantalum is superior to barium or iodine because 1) it is more radiopaque; 2) it outlines in good detail airways from the trachea to those less than 1 mm in diameter without serious effects on lung function; 3) it is chemically inert so it causes no inflammation in the airways or lungs; 4) it is cleared rapidly from the airways; and 5) it can be delivered as an aerosol of powder via the trachea as well as via a catheter in the airway. The technique can be used to study the effects of various physiologic alterations and pharmacologic agents on the diameter of the airways. Powdered tantalum can also be used to study mucosal changes, to locate substances in the lumen and to study lung clearance; it should be applicable to the study of the upper airways and sinuses.
Nadel et al. (1968) studied this question.