[Experimental study of detectability of simulated lung nodule on computed radiography system using various X-ray beam qualities].

The purpose of this study was to discuss the optimal X-ray beam quality for detection of simulated lung nodule on a computed radiography system. We set up four types of X-ray beam quality (90 kV, 120 kV, 150 kV, and 120 kV + gadolinium filter), and kept the incident dose on the patient at 0.3 mGy. A receiver operating characteristic (ROC) analysis and a granularity measurement were used to evaluate the relationship between the detection of a low-contrast object and X-ray beam quality. As a result, the areas under the ROC curve (AUC) of 90 kV and 120 kV + gadolinium filter were significantly superior to those of 120 kV and 150 kV (p<0.05). However, a significant difference was not observed between 90 kV and 120 kV + gadolinium filter, 120 kV and 150 kV. The order of the granularity values gave good agreement with the results of visual evaluation. In conclusion, we considered that the optimal X-ray beam quality was 90 kV or 120 kV + gadolinium filter.