[Bedside thoracic radiography: a comparison between 3 different types of grid].

Bedside chest radiography accounts for an increasingly large portion of all chest X-ray examinations. Nevertheless, image quality is often poor mainly because of scattered radiations which decrease image contrast. Moreover, usually no grid is employed because of difficult beam alignment. This work was aimed at comparing different radiologic grids for bedside chest radiography. Fifty patients submitted to two bedside chest radiographs in 24 hours were studied. All the patients underwent the first exam with a Kodak InSight cassette with a newly-designed (columnar type) grid inside, while the second exam was performed with a conventional 8:1 focused lead-strip grid (Gilardoni) in 25 patients and with a 6:1 focused lead-strip grid (Gilardoni) in the extant 25 patients. Both grids were assembled in a Kodak InSight radiographic cassette. Three independent radiologists evaluated film quality, focusing on the depiction of some anatomical structures--e.g., the tracheobronchial tree, the retrocardiac lung, and devices. Seventy-five examinations were obtained for each grid and for each evaluated structure and graded as "good", "acceptable" and "poor". In the 6:1 vs columnar grid test, the highest rate of "good" and "acceptable"--i.e., diagnostic--findings was observed with the columnar grid in evaluating pulmonary vessels (71/75); the highest rate of "poor" findings was obtained with the same grid in evaluating tracheal bifurcation (43/75). In the 8:1 vs columnar grid test, the highest rate of diagnostic findings was shown by the conventional grid in evaluating retrocardiac lung parenchyma and by the columnar grid for pulmonary vessels (69/75); the highest rate of "poor" findings was obtained with the columnar grid in evaluating tracheal bifurcation (40/75). The statistical analysis of the results (Wilcoxon test) was made to compare the two conventional grids with the new columnar one. Statistically significant differences were observed between the 8:1 grid and the columnar grid to evaluate the bronchial tree. No differences were observed between the 8:1 grid and the columnar grid. Furthermore, to determine the effects of different degrees of grid decentering on image quality, a series of exposures was made using a lung-chest phantom. The grids, both the lead-stripe and the columnar one, were comparable. The higher-ratio grid proved better in evaluating tiny details. The columnar grid exhibited better tolerance to X-ray beam and to grid decentering.