Image Quality Evaluation of Digital Radiography (DR) System Using Howlett chart

Abstract

The purpose of this study is a comparison of image quality between two CCD (charged coupled device) cameras of the DR system using a Howlett chart. The DR system evaluated here is equipped with CCD cameras of 1 (1k) and 4 (2k) million pixels, respectively. The differences in image quality were compared under a variety of exposure conditions, and evaluated with Howlett chart. It was found that the image quality of both systems improved with increasing surface doses up to 0.15 mGy. For surface doses from 0.15 mGy to 0.7 mGy, the increase of the surface dose resulted in no significant improvement in the image quality of either system. For surface doses exceeding 0.7 mGy, the image quality of both systems deteriorated rapidly with increasing doses due to halation in the images. For surface doses of less than 0.32 mGy, the matrix sizes (1k or 2k) demonstrated no significant differences in image quality. For surface doses from 0.32 to 0.7 mGy, image quality of the 2k system was, on the whole, better than that of the 1k system (p<0.05). The surface dose in clinical practice is recommended not to exceed 0.15 mGy. Doses of more than 0.15 mGy merely result in increased patient exposure. Longer exposure times may cause blurred images because of the motion of the organs and increased surface doses may require a larger focal spot. As a result, image quality will not be improved by increasing surface dose beyond 0.15 mGy.