title: Pulmonary nodule volumetric measurement variability as a function of CT slice thickness and nodule morphology.
abstract: OBJECTIVE
  The purpose of our study was to assess differences in volumetric measurements of pulmonary nodules obtained using different CT slice thicknesses; correlate these differences with nodule size, shape, and margination; and compare measurements generated by two different software packages.
  
  
  METHODS
  Seventy-five individual nodules identified on 29 lowdose, unenhanced, MDCT chest examinations were selected for volumetric analysis. Each image data set was reconstructed in three ways (slice thickness/reconstruction interval): 1.25 mm/0.625 mm, 2.5 mm/2 mm, and 5 mm/2.5 mm. Volumetric measurements were made on all 75 nodules at 1.25- and 2.5-mm slice thicknesses and on 57 of 75 nodules at the 5-mm thickness using Volume Analysis software. For 69 of 75 nodules, measurements were obtained on 1.25- and 2.5-mm-thick sections using a different commercially available software system, LN500 R2 software. Volume variability between different slice thicknesses was correlated with nodule diameter, shape, and margination using multiple linear regression. Percent differences between measurements obtained with the two software systems were calculated. Significance of relative volume differences between slice thicknesses and software packages was assessed using a one-sample Student's t-test.
  
  
  RESULTS
  Although statistically significant differences in volumes between different section thicknesses were seen only for the tiny nodule size group, many individual nodules showed substantial volume variation. Significant differences were seen in nodule volume variability for smaller nodules (3-10 mm) compared with larger nodules (> or = 11 mm) (p < 0.0001), as well as spiculated compared with smooth nodules, within a single size group (p < 0.05). No effect of nodule shape (round vs elongated) was noted. Statistically significant differences in measurements obtained with the two software systems were seen only with 2.5-mm-thick sections (p = 0.001).
  
  
  CONCLUSIONS
  CT slice thickness variation resulted in significant differences in volume measurements for tiny nodules. A spiculated margin was shown to have a significant effect on nodule volume variability within a single size group. Use of different software packages resulted in significant volume measurement differences at the 2.5-mm CT slice thickness.
authors.affiliation: Department of Radiology, University of Michigan, 1500 E Medical Center Dr., Ann Arbor, MI 48109, USA. mpetrou@umich.edu
authors.forename: Myria
authors.initials: M
authors.lastname: Petrou
authors.forename: Leslie E
authors.initials: LE
authors.lastname: Quint
authors.forename: Bin
authors.initials: B
authors.lastname: Nan
authors.forename: Laurence H
authors.initials: LH
authors.lastname: Baker
mesh_terms: D000465:Algorithms; D019412:Anatomy, Cross-Sectional / Q000379:methods*; D001185:Artificial Intelligence; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D016247:Information Storage and Retrieval / Q000379:methods; D008175:Lung Neoplasms / Q000000981:diagnostic imaging; D010363:Pattern Recognition, Automated / Q000379:methods*; D011856:Radiographic Image Enhancement / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D003074:Solitary Pulmonary Nodule / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*