Dissertation Abstract

Evaluation of image quality and patient radiation dose in digital radiology

X-ray radiographs are the most frequently obtained images in radiology. Until recently, most of them were still acquired with screen-film techniques. The last years, digital radiography detectors are gaining importance as medical imaging departments are moving towards a completely integrated digital environment (PACS/HIS/RIS). When introducing these new detectors into clinical practice, they should perform at least as good as screen-film radiography systems with respect to image quality and patient radiation dose.In the first part of present thesis, the image quality and dose performance of different digital acquisition systems were compared. For the assessment of the image quality, patient chest images were scored according to the European Guidelines on Quality Criteria for Diagnostic Radiographic Images. In addition, CDRAD 2.0 contrast-detail phantom acquisitions were used for an objective measure of the low-contrast performance.The image quality for current digital chest radiography systems was found to be superior compared to conventional screen-film systems. Flat-panel detectors based on cesium iodide and amorphous silicon, resulted in the best overall performance. Compared to a conventional screen-film system, the latter detector achieved a dose reduction of more than 60%. In flat-panel systems based on amorphous selenium, on the other hand, similar dose levels as measured in state-of-the-art screen-film chest radiography must be applied. Similarly, no significant dose reductions were found for storage phosphor plate chest imaging.Image quality analysis based on patient images correlated very well with the more objective and less time-consuming contrast-detail analysis. Hence, the latter methodology may be an interesting tool for implementation in a quality assurance program for digital radiography.In the second part of this thesis, digital image presentation was studied using digital CDRAD 2.0 and CDMAM 3.4 contrast-detail phantom acquisitions. It was shown that soft-copy reading can significantly improve the contrast-detail detectability compared to hard-copy presentation.The low-contrast performance of medical grade LCD devices of different matrix resolutions was compared with that of a state-of-the-art greyscale CRT monitor. The contrast-detail analysis showed that a monitor with 3-megapixel or higher is recommended for the application in digital chest radiography. For digital mammography, a 5-megapixel monitor should be the first choice.

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