Abstract
Objectives
The objectives of this study were to quantify the impact of image post-processing parameters on the apparent renal stone size, and to quantify the intra- and inter-reader variability in renal stone size estimation.
Methods
Fifty CT datasets including a renal or ureteral stone were included retrospectively during a prospective inclusion period. Each of the CT datasets was post-processed in different ways regarding slice thickness, slice increment and window setting. In the first part of the study a single reader repeated size estimations for the renal stones using different post-processing parameters. In the intra-reader variability experiment one reader reported size estimations for the same images with a one-week interval. The inter-reader variability data were obtained from 11 readers reporting size estimations for the same renal stones.
Results
The apparent stone size differed according to image post-processing parameters with the largest mean differences seen with regard to the window settings experiment (1.5 mm, p < 0.001) and slice thickness (0.8 mm, p < 0.001). Changes in parameters introduced a bias and a pseudo-random variability. The inter-reader variability was considerably larger than the intra-reader variability.
Conclusion
Our results indicate a need for the standardisation of making measurements on CT images.
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Acknowledgements
Many thanks to T Eriksson for assistance in selecting cases and to the participating readers at the radiology department: T Birgersson, P Dimitriou, T Eriksson, A Gregorius, J Jendeberg, W Krauss, M Lundin, A Mood, H Skoglund and T Westermark.
This work has been conducted in collaboration with the Center for Medical Image Science and Visualization (CMIV) at Linköping University, Sweden. CMIV is acknowledged for the provision of financial support and access to leading edge research infrastructure. The study was funded in part by a grant from The Knowledge Foundation, Stockholm, Sweden.
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Lidén, M., Andersson, T. & Geijer, H. Making renal stones change size—impact of CT image post processing and reader variability. Eur Radiol 21, 2218–2225 (2011). https://doi.org/10.1007/s00330-011-2171-x
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DOI: https://doi.org/10.1007/s00330-011-2171-x