Independent evaluation and comparison of digital radiography image quality in nine major imaging centers affiliated to Shiraz University of Medical Sciences

To audit image quality (IQ) of computed radiography (CR), indirect digital radiography (IDR) and direct digital radiography (DDR) systems used in nine centers affiliated to Shiraz University of Medical Sciences, Shiraz, Iran.

Sixteen imaging units (four CR, five IDR and seven DDR) employing 26 image receptors were assessed. After ensuring the accuracy of X-ray generator performance, IQ was evaluated using a contrast-detail phantom. Spatial resolution, low contrast detectability (LCD) and dynamic range (as subjective indicators) and contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) (as objective quantities) were evaluated. Further, the IQ evaluators of different image receptor types were compared. 

One CR unit failed the X-ray generator performance tests and was excluded from the rest of the study. All 25 remaining image receptors passed the LCD, CNR and SNR criteria. Contrast dynamic range failed in 19 receptors, 17 of them being within a ‘borderline’ failure range. Spatial resolution failed in 18 detectors; 12 of them were borderline failures. The IDR units performed better than the CR and DDR detectors in terms of LCD (p=0.012) and SNR (p=0.007). 

All of the evaluated receptors passed the majority the IQ tests (both physical indicators and one out of the three subjective ones), while contrast dynamic range and spatial resolution of the majority of the failed detectors were borderline failures. Significant differences were observed in IQ among the three image receptors types. The results suggest the need for an improved maintenance, quality assurance and audit program.