Exposure index and radiographic noise of an indirect flat-panel detector system for various X-ray beam qualities

In digital radiography (DR) systems, the sensitivity index, also known as the exposure indicator, exhibits unique behavior, depending on the manufacturer. The exposure index (EI) was introduced by the International Electrotechnical Commission to standardize the sensitivity indices of DR systems produced by different manufacturers for general radiography. This EI value is directly proportional to the dose incident on the imaging detector, providing valuable insight into exposure dose levels and radiographic noise. Recently, technological advancements have enabled some DR systems to display the EI value on the console immediately after exposure. This study investigated the characteristics of the displayed EI value and radiographic noise for an indirect flat-panel detector across four X-ray beam qualities based on added aluminum filters: RQA3, 5, 7, and 9. The displayed EI values for all the X-ray beam qualities proportionally increased to the dose incident on the detector. However, the displayed EI values for RQA3 deviated from those for RQA5, 7, and 9 at the same doses incident on the imaging detector. Furthermore, the Wiener spectrum (WS) was used to evaluate radiographic noise. For similar EI values, the WS of RQA3, which had the highest dose incident on the imaging detector, was slightly lower than those of other X-ray beam qualities. Our findings suggest that the relationship between the displayed EI and radiographic noise varies with the X-ray beam quality.