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Comparison of Indirect CsI/a:Si and Direct a: Se Digital Radiography

An assessment of contrast and detail visualization


*Frank Fischbach, Department of Radiology, Charité, Campus Virchow-Klinikum, Humboldt-University Medical School, Augustenburgerplatz 1, DE-13353 Berlin, Germany.
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Purpose:  To assess and quantify the image quality at two dose levels for an amorphous Silicon (a:Si) Cesium Iodide (CsI) flat panel system compared with a direct amorphous Selenium (a:Se) digital radiography system.

Material and Methods:  A contrast detectability test was performed employing the CDRAD-phantom at mAs-values leading to approximately equal phantom entrance doses of 41.4, 57.9, 75.1 and 120.8 µGy for the a:Se and 39.9, 58.4, 75.6 and 117.9 µGy for the CsI system. Images were presented to 4 independent observers. For quantitative comparison, the image quality figure (IQF) was calculated. Statistical analysis was performed using Pearson's correlation and the Wilcoxon test. A ROC-analysis was performed employing the TRG-phantom in a high- and a low-dose setting leading to entrance doses of 126.2 and 35 µGy for the direct, and 125.9 and 34.4 µGy for the indirect system. Statistical significance was evaluated using the Wilcoxon test

Results:  The flat panel a:Si digital system provided superior results compared with the a:Se drum digital system with respect to low-dose settings for CDRAD-phantom and ROC-analysis, ensuring a better image quality with respect to contrast and detail detectability. Higher-dose settings provided similar results for both systems.

Conclusion:  Image quality of a:Si flat panel digital radiography proved to be superior to a:Se drum digital radiography using low-dose settings. If the primary target is dose reduction indirect flat panel technology should be used.