title: Pneumothorax size measurements on digital chest radiographs: Intra- and inter- rater reliability.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Thoracic Medicine, Haukeland University Hospital, Jonas Lies vei 65, NO-5021 Bergen, Norway. Electronic address: andreas.thelle@helse-bergen.no.
authors.forename: Andreas
authors.initials: A
authors.lastname: Thelle
authors.affiliation: Norwegian Registry for Long-Term Mechanical Ventilation, Department of Thoracic Medicine, Haukeland University Hospital, Jonas Lies vei 65, NO-5021 Bergen, Norway; Norwegian Registry for Chronic Obstructive Pulmonary Disease, Department of Thoracic Medicine, Haukeland University Hospital, Jonas Lies vei 65, NO-5021 Bergen, Norway. Electronic address: Miriam.Gjerdevik@igs.uib.no.
authors.forename: Miriam
authors.initials: M
authors.lastname: Gjerdevik
authors.affiliation: Department of Thoracic Medicine, Haukeland University Hospital, Jonas Lies vei 65, NO-5021 Bergen, Norway. Electronic address: thomas.grydeland@helse-bergen.no.
authors.forename: Thomas
authors.initials: T
authors.lastname: Grydeland
authors.affiliation: Department of Occupational Medicine, Haukeland University Hospital, Jonas Lies vei 65, NO-5021 Bergen, Norway. Electronic address: trude.duelien.skorge@helse-bergen.no.
authors.forename: Trude D
authors.initials: TD
authors.lastname: Skorge
authors.affiliation: Norwegian Centre for Violence and Traumatic Stress Studies, Oslo, Norway; Centre for Child and Adolescent Mental Health, Eastern and Southern Norway, P.O.Box 4623 Nydalen, NO-0405 Oslo, Norway; Centre for Clinical Research, Haukeland University Hospital,Jonas Lies vei 65, NO-5021 Bergen, Norway. Electronic address: tore.wentzel-larsen@nkvts.unirand.no.
authors.forename: Tore
authors.initials: T
authors.lastname: Wentzel-Larsen
authors.affiliation: Department of Clinical Science, University of Bergen, Jonas Lies vei 65, NO-5021, Norway. Electronic address: Per.Bakke@k2.uib.no.
authors.forename: Per S
authors.initials: PS
authors.lastname: Bakke
mesh_terms: D000465:Algorithms; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008297:Male; D015588:Observer Variation; D010994:Pleura / Q000000981:diagnostic imaging; D011030:Pneumothorax / Q000000981:diagnostic imaging*; D011446:Prospective Studies; D011856:Radiographic Image Enhancement; D013902:Radiography, Thoracic / Q000706:statistics & numerical data*; D015203:Reproducibility of Results; D012189:Retrospective Studies
keywords: Digital chest radiograph; Interrater reliability; Intrarater reliability; Pneumothorax size measurement; Rhea’ method