title: A controlled statistical study to assess measurement variability as a function of test object position and configuration for automated surveillance in a multicenter longitudinal COPD study (SPIROMICS).
abstract: OBJECTIVE
  A test object (phantom) is an important tool to evaluate comparability and stability of CT scanners used in multicenter and longitudinal studies. However, there are many sources of error that can interfere with the test object-derived quantitative measurements. Here the authors investigated three major possible sources of operator error in the use of a test object employed to assess pulmonary density-related as well as airway-related metrics.
  
  
  METHODS
  Two kinds of experiments were carried out to assess measurement variability caused by imperfect scanning status. The first one consisted of three experiments. A COPDGene test object was scanned using a dual source multidetector computed tomographic scanner (Siemens Somatom Flash) with the Subpopulations and Intermediate Outcome Measures in COPD Study (SPIROMICS) inspiration protocol (120 kV, 110 mAs, pitch = 1, slice thickness = 0.75 mm, slice spacing = 0.5 mm) to evaluate the effects of tilt angle, water bottle offset, and air bubble size. After analysis of these results, a guideline was reached in order to achieve more reliable results for this test object. Next the authors applied the above findings to 2272 test object scans collected over 4 years as part of the SPIROMICS study. The authors compared changes of the data consistency before and after excluding the scans that failed to pass the guideline.
  
  
  RESULTS
  This study established the following limits for the test object: tilt index ≤0.3, water bottle offset limits of [-6.6 mm, 7.4 mm], and no air bubble within the water bottle, where tilt index is a measure incorporating two tilt angles around x- and y-axis. With 95% confidence, the density measurement variation for all five interested materials in the test object (acrylic, water, lung, inside air, and outside air) resulting from all three error sources can be limited to ±0.9 HU (summed in quadrature), when all the requirements are satisfied. The authors applied these criteria to 2272 SPIROMICS scans and demonstrated a significant reduction in measurement variation associated with the test object.
  
  
  CONCLUSIONS
  Three operator errors were identified which significantly affected the usability of the acquired scan images of the test object used for monitoring scanner stability in a multicenter study. The authors' results demonstrated that at the time of test object scan receipt at a radiology core laboratory, quality control procedures should include an assessment of tilt index, water bottle offset, and air bubble size within the water bottle. Application of this methodology to 2272 SPIROMICS scans indicated that their findings were not limited to the scanner make and model used for the initial test but was generalizable to both Siemens and GE scanners which comprise the scanner types used within the SPIROMICS study.
authors.affiliation: Departments of Radiology and Biomedical Engineering, University of Iowa, Iowa City, Iowa 52242.
authors.forename: Junfeng
authors.initials: J
authors.lastname: Guo
authors.affiliation: Department of Statistics and Actuarial Science, University of Iowa, Iowa City, Iowa 52242.
authors.forename: Chao
authors.initials: C
authors.lastname: Wang
authors.affiliation: Department of Statistics and Actuarial Science, University of Iowa, Iowa City, Iowa 52242.
authors.forename: Kung-Sik
authors.initials: KS
authors.lastname: Chan
authors.affiliation: Department of Electrical and Computer Engineering, University of Iowa, Iowa City, Iowa 52242.
authors.forename: Dakai
authors.initials: D
authors.lastname: Jin
authors.affiliation: Department of Electrical and Computer Engineering, University of Iowa, Iowa City, Iowa 52242.
authors.forename: Punam K
authors.initials: PK
authors.lastname: Saha
authors.affiliation: Department of Radiology, University of Iowa, Iowa City, Iowa 52242.
authors.forename: Jered P
authors.initials: JP
authors.lastname: Sieren
authors.affiliation: Departments of Medicine and Epidemiology, Columbia University Medical Center, New York, New York 10032.
authors.forename: R G
authors.initials: RG
authors.lastname: Barr
authors.affiliation: Department of Medicine, Division of Pulmonary and Critical Care Medicine, University of Michigan, Ann Arbor, Michigan 48109.
authors.forename: MeiLan K
authors.initials: MK
authors.lastname: Han
authors.affiliation: Department of Radiology, University of Michigan, Ann Arbor, Michigan 48109.
authors.forename: Ella
authors.initials: E
authors.lastname: Kazerooni
authors.affiliation: Department of Medicine, University of California, Los Angeles, California 90095.
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Cooper
authors.affiliation: Department of Biostatistics, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: David
authors.initials: D
authors.lastname: Couper
authors.affiliation: Departments of Radiology and Biomedical Engineering, University of Iowa, Iowa City, Iowa 52242.
authors.forename: John D
authors.initials: JD
authors.lastname: Newell
authors.affiliation: Departments of Radiology, Medicine and Biomedical Engineering, University of Iowa, Iowa City, Iowa 52242.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Hoffman
mesh_terms: D000388:Air; D003627:Data Interpretation, Statistical; D008137:Longitudinal Studies; D008953:Models, Anatomic; D061330:Multidetector Computed Tomography / Q000295:instrumentation / Q000379:methods*; D010363:Pattern Recognition, Automated / Q000379:methods*; D019047:Phantoms, Imaging; D011786:Quality Control; D014867:Water
chemical_list: D014867:Water