Bronchograms:
Bronchograms should be performed under fluoroscopy preferentially with biplane imaging with AP and lateral views or with the recent 3D dynaCT reconstructions. Bronchogram can accurately determine the exact calibre of the smaller airways which may not be accessible by bronchoscopy. Figure 8 demonstrates the accuracy of this technique in comparison to a simultaneous CT that shows a left main bronchus artefact on CT only - this may be misleading especially for surgical planning. If contrast extends into the alveoli it may also give valuable information on lobar and sub segmental bronchial supply. Whilst only a small volume ( typically 0.25  to 0.5ml/kg) of  contrast agent are used (Omnipaque or Visipaque) it is rapidly resolved and does not usually cause bronchial irritation. Radiopaque per fluorocarbon is the ideal contrast agent as this is inert and rapidly evaporates following intracheal  administration.41 Gentle balloon dilation to access the tracheal calibre and if there is fixed stenosis can also be done with a low pressure balloon (figure 9) or to assess the airway for potential stenting.  Bronchogram and balloon dilations form the cornerstone of post-operative care to treat recurrent stenosis at the operative site.
A single static bedside AP bronchogram in an intubated patient can be invaluable to rapidly diagnose long segment tracheal stenosis and the extent of tracheobronchial involvement (figure 11). Here, a standard chest X-ray is performed with 0.25 to 0.5ml/kg  of contrast agent via a thin 6 Fr feeding tube positioned at the end of the endotracheal tube. The contrast is injected rapidly and an image is obtained 3 to 5 seconds after intratracheal injection under expiration. Dense hold-up of contrast indicates significant tracheal obstruction as normally the contrast agent dissipates rapidly into the bronchi creating the typical tram track appearance that lines the airway. This can be performed at the bedside in intensive care if the patient is too unstable to move or the  stenosis is too small for even a bronchoscopy to assess. Barium swallow is to delineate the oesophagus very limited diagnostic value.