[Thoracic radiography. Comparison of asymmetric screen-film, technic of mechanical homogenization, and conventional technics].

This study was aimed at comparing three different systems, i.e., asymmetric screen-film, mechanical homogenized and conventional techniques, in standing frontal and lateral plain radiographs of the chest. Two hundred consecutive patients with normal posteroanterior (PA) and lateral films were randomly subdivided into 4 groups. Each group was submitted to chest radiographs with a different technique: asymmetric screen-film systems (InSight HC and High Light GCA), mechanical homogenized (Tau-Gil Homogenized) and conventional high-kilovoltage techniques. The exposure values for frontal projections ranged 110 kV (InSight HC) to 141 kV (Tau-Gil), while for lateral projections they ranged 123 kV (conventional technique) to 143 kV (Tau-Gil). Statistically significant differences were observed between the two asymmetric systems as regards exposure values, High Light exhibiting higher mean values in the frontal projection (t-test p < 0.05). Image quality was studied jointly by 3 experienced chest radiologists. The observers were asked to grade, on a 3-point ordinal scale, the conspicuity of mediastinal borders, of pulmonary vessels and of selected areas of lung parenchyma (i.e., retrocardiac, retrosternal and apical regions), as well as overall image quality on the frontal projection. The statistical analysis of paired differences was performed with the Mann-Whitney U-test. The asymmetric and the mechanical homogenized techniques were much better than the conventional technique in depicting tracheobronchial tree, retrocardiac parenchyma, azygos-esophageal recess and thoracic spine (p < 0.05). The mechanical homogenized system provided best overall image quality on frontal films, being superior to both InSight HC and conventional techniques, but not to the High Light GCA system; only the frontal projection obtained with the homogenized technique was compared, no filter being available for the lateral projection. When the two asymmetric systems were compared, the High Light system better depicted vascular structures on frontal films (p < 0.05), while apical areas were better demonstrated with the InSight system, namely with lateral films (p < 0.05).