title: Small irregular pulmonary nodules in low-dose CT: observer detection sensitivity and volumetry accuracy.
abstract: OBJECTIVE
  The purpose of this study is to evaluate observer detection and volume measurement of small irregular solid artificial pulmonary nodules on 64-MDCT in an anthropomorphic thoracic phantom.
  
  
  METHODS
  Forty in-house-made solid pulmonary nodules (lobulated and spiculated; actual volume, 5.1-88.4 mm3; actual CT densities, -51 to 157 HU) were randomly placed inside an anthropomorphic thoracic phantom with pulmonary vasculature. The phantom was examined on two 64-MDCT scanners, using a scan protocol as applied in lung cancer screening. Two independent blinded observers screened for pulmonary nodules. Nodule volume was evaluated semiautomatically using dedicated software and was compared with the actual volume using an independent-samples t test. The interscanner and interobserver agreement of volumetry was assessed using Bland-Altman analysis.
  
  
  RESULTS
  Observer detection sensitivity increased along with increasing size of irregular nodules. Sensitivity was 100% when the actual volume was at least 69 mm3, regardless of specific observer, scanner, nodule shape, and density. Overall, nodule volume was underestimated by (mean±SD) 18.9±11.8 mm3 (39%±21%; p<0.001). The relative interscanner difference of volumetry was 3.3% (95% CI, -33.9% to 40.4%). The relative interobserver difference was 0.6% (-33.3% to 34.5%).
  
  
  CONCLUSIONS
  Small irregular solid pulmonary nodules with an actual volume of at least 69 mm3 are reliably detected on 64-MDCT. However, CT-derived volume of those small nodules is largely underestimated, with considerable variation.
authors.affiliation: 1 Department of Radiology, University of Groningen, University Medical Center Groningen, PO Box 30.001, Groningen 9700 RB, The Netherlands.
authors.forename: Xueqian
authors.initials: X
authors.lastname: Xie
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Willemink
authors.forename: Pim A
authors.initials: PA
authors.lastname: de Jong
authors.forename: Peter M A
authors.initials: PM
authors.lastname: van Ooijen
authors.forename: Matthijs
authors.initials: M
authors.lastname: Oudkerk
authors.forename: Rozemarijn
authors.initials: R
authors.lastname: Vliegenthart
authors.forename: Marcel J W
authors.initials: MJ
authors.lastname: Greuter
mesh_terms: D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging*; D015588:Observer Variation; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D003074:Solitary Pulmonary Nodule / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation* / Q000379:methods*; D047368:Tumor Burden