The clinical significance of modifying X-ray tube current-time product based on prior image deviation index for digital radiography

Abstract

Purpose: The absorbed dose at the image receptor in digital X-ray systems increases with an incorrect adjustment of the X-ray tube current-time product (mAs). Accordingly, the exposure index, target exposure index, and deviation index (DI) are proposed as absorbed dose optimization tools. We aimed at reducing the variation of DI in a short period by employing the mAs value determined by previously used mAs and DI.

Methods: We developed software that automatically calculates mAs for subsequent X-ray examinations based on mAs and DI values from prior examinations. Portable chest X-ray examinations in an intensive care unit (ICU) were performed for 16 weeks. The software was not used for the first 10 weeks in 406 cases and was used for the remaining 6 weeks in 216 cases. The changes in the non-conformance rate of DI for 16 weeks were evaluated using the p-chart used for quality control. The effect of the software on image noise was also evaluated.

Results: In total, 42% of cases had a DI range of -1 to 1 without using the software; this increased to 81% when using the software. Averages and variances of DI in cases with and without the software demonstrated statistically significant differences. From the p-chart, the non-conformance rate of DI was shown to decrease when using software. The software also worked for reducing the variation in image noise.

Conclusions: Our method reduced the variation in DI in a short period of time.

Keywords: Deviation index; Portable X-ray digital radiography; Statistical quality control.