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

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Purpose: 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.Materials and Methods: 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 dual-energy subtracted chest radiograph (DES image). The diameter of the simulated nodules was 8-, 10-, and 12 mm; 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.Results: For -450 HU nodules the mean area under the ROC curve (AUC) without and with DES images was 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).Conclusion: 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.