Effects of dual-energy subtraction chest radiography on detection of small pulmonary nodules with varying attenuation: receiver operating characteristic analysis using a phantom study

The aim of this study was to investigate the detectability of simulated pulmonary nodules with different X-ray attenuation by flat-panel detector (FPD) chest radiography using a dual-exposure dual-energy subtraction (DES) technique. Using a FPD radiography system, we obtained 108 sets of chest radiographs of a chest phantom. They consisted of 54 sets each of chest radiographs with and without simulated nodules. Each data set contained a standard and a corresponding dualenergy subtracted chest radiograph (DES image). The diameters of the simulated nodules were 8, 10, and 12 mm, respectively; nodules of each size manifested attenuation of -450, -200, and 30 Hounsfield units (HU). We performed receiver operating characteristic (ROC) analysis to compare the observers' performance in detecting nodules. For the -450 HU nodules the mean areas under the ROC curve (AUC) without and with DES images were 0.66 and 0.77, respectively; the difference was significant (paired t-test, P < 0.01). For nodules with -200 and 30 HU, there was no significant difference in the AUC value (0.79 vs. 0.77, P = 0.13; 0.92 vs. 0.94, P = 0.17, respectively). The addition of DES images to standard chest radiographs improved the performance of radiologists charged with detecting simulated nodules with an attenuation of -450 HU.