Pneumothorax size measurements on digital chest radiographs: Intra- and inter- rater reliability

Detailed and reliable methods may be important for discussions on the importance of pneumothorax size in clinical decision-making. Rhea's method is widely used to estimate pneumothorax size in percent based on chest X-rays (CXRs) from three measure points. Choi's addendum is used for anterioposterior projections. The aim of this study was to examine the intrarater and interrater reliability of the Rhea and Choi method using digital CXR in the ward based PACS monitors.

Three physicians examined a retrospective series of 80 digital CXRs showing pneumothorax, using Rhea and Choi's method, then repeated in a random order two weeks later. We used the analysis of variance technique by Eliasziw et al. to assess the intrarater and interrater reliability in altogether 480 estimations of pneumothorax size.

Estimated pneumothorax sizes ranged between 5% and 100%. The intrarater reliability coefficient was 0.98 (95% one-sided lower-limit confidence interval C 0.96), and the interrater reliability coefficient was 0.95 (95% one-sided lower-limit confidence interval 0.93).

This study has shown that the Rhea and Choi method for calculating pneumothorax size has high intrarater and interrater reliability. These results are valid across gender, side of pneumothorax and whether the patient is diagnosed with primary or secondary pneumothorax.