Quantitative Analysis Methods Using Histogram and Entropy for Detector Performance Evaluation According to the Sensitivity Change of the Automatic Exposure Control in Digital Radiography

The purpose of this study is to evaluate detector performance using histogram and entropy analysis according to the sensitivity change of the automatic exposure control (AEC). The experiment was performed as follows: The sensitivity of the detector was analyzed through a normalized histogram with sensitivities of S200, S400, S800, and S1000 of the AEC; the entropy of the image was then analyzed, and the signal volume of the detector was evaluated according to the sensitivity change. As the sensitivity of the AEC was increased from S200 to S1000, the histogram showed underflow, quantization separation, and dynamic range discrepancy. In addition, entropy showed a decrease as sensitivity was set higher; in particular, entropy degradation was more prominent at sensitivities above S800. Through the histogram and entropy analysis, it was concluded that the detector does not reproduce the sensitivity and signal volume accurately when the sensitivity of the AEC is set high in performance evaluation.