Standardization of image quality in dynamic chest radiography: a determination procedure of individualized exposure settings based on the data from plain chest radiography.

Abstract

In plain chest radiography (CXR), automatic exposure control (AEC) is generally used to standardize image quality. In contrast, dynamic chest radiography (DCR) systems preliminarily require manual setting of tube current-time products (mAs value). Body mass index (BMI) of patients is one of the indexes to determine the mAs value; however, standardization is limited because the anatomical differences are not considered. In this study, for further standardization, we propose a practical procedure to determine the individual mAs value of DCR using data obtained from CXR. To evaluate its effectiveness, we retrospectively analyzed 97 patients who underwent both CXR and DCR on the same day. DCR was performed in the following procedures: (1) obtain the relationship between the mAs value and the exposure indicator (S value, Konica Minolta, Inc.) obtained in CXR acquisition, (2) calculate the mAs value of DCR for the target S value of 2500, and (3) record the S value in DCR. The tube voltages for CXR and DCR were set to 120 kV and 100 kV with a copper filter, respectively. The differences in exposure doses were corrected by measuring the air kerma using a CdTe detector. As a result, the S values of CXR and DCR were 133 ± 13 (Coefficient of Variation (CV) = 9.9%) and 2629 ± 207 (CV = 7.9%), respectively, which were not dependent on the patient size based on evaluating the S values of five classified BMI groups. In conclusion, our proposed procedure enables standardization of the image quality in DCR by optimizing the patient-specific exposure conditions.