Technical aspects of twin screen-film chest radiography: Cost effective lung and mediastinal imaging

Objective: To determine the sensitometry and 'cross-talk' of a twin screen-film cassette and to assess its clinical potential. Materials and Methods: The twin cassette utilises two sets of screens, divided by filter material, to provide an optimised image of the mediastinum and the lungs. The exposure difference for the two images was measured sensitometrically. The contribution to film density of visible light and K-characteristic radiation, from adjacent screens in the absence of a dividing filter, was investigated. Result: Clinical experience indicated that an exposure difference of 3.4 between the front and back screens, was optimal. Visible light and K- characteristic radiation from the front screens, contributed up to 20 and 24% respectively, of the back film exposure and screen absorbed energy respectively. This was reduced to 0 and 6% with the use of the filter. Conclusions: The twin screen-film cassette provides extended latitude to enable optimal visualisation of the lung and mediastinal regions. Adjacent screen 'cross-talk' has been overcome to allow standard and portable chest applications.