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Eur Radiol. 2011 Oct;21(10):2218-25. doi: 10.1007/s00330-011-2171-x. Epub 2011 Jun 23.

Making renal stones change size-impact of CT image post processing and reader variability.

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School of Health and Medical Sciences, Örebro University, 701 82, Örebro, Sweden.



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.


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.


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.


Our results indicate a need for the standardisation of making measurements on CT images.

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