Abstract
Background: The introduction of digital detectors in the radiology predicted a dose reduction. Due to the dynamic range, radiographs of sufficient quality can be produced with a lower detector air kerma (DAK). However, this reduction was not observed. Some authors indicate a creep towards higher DAK, explained by a better appreciation of the radiographs due to a higher contrast-to-noise ratio. Methodology: To investigate the relation between the DAK and the appreciation of image quality by radiologists, 172 anterior-posterior (AP) radiographs of the knee and 152 radiographs of the pelvis were collected in 19 radiology centres. A Visual Grading Analysis (VGA) with a five-point scale was used to judge the image quality of seven different anatomic structures. The mid-point of the scale (3) was equalized to diagnostic image quality. Six experienced radiologists scored both datasets, in a controlled environment, with ViewDex®. Every observer received instructions and a training dataset. Moreover, twenty radiographs were repeated to determine intra-observer variability. Results: The intra-observer variability was not significant (p>0.05) for both datasets. The knee AP obtained a VGAS score of 3.91, the pelvis AP obtained a VGAS score of 3.71. In both cases, the inter-observer correlation was high and significant. The correlation between the VGAS and the DAK (0.41μGy – 6.18μGy) was not significant in either of the cases; neither did other analysises based on technical parameters. Conclusion: The VGA revealed an image quality higher than diagnostic necessary. Based on the DAK, an overexposure is suspected. The relation between DAK and the appreciation has to be further investigated in detail.
