title: Effect of reconstruction methods and x-ray tube current-time product on nodule detection in an anthropomorphic thorax phantom: A crossed-modality JAFROC observer study.
abstract: OBJECTIVE
  To evaluate nodule detection in an anthropomorphic chest phantom in computed tomography (CT) images reconstructed with adaptive iterative dose reduction 3D (AIDR(3D)) and filtered back projection (FBP) over a range of tube current-time product (mAs).
  
  
  METHODS
  Two phantoms were used in this study: (i) an anthropomorphic chest phantom was loaded with spherical simulated nodules of 5, 8, 10, and 12 mm in diameter and +100, -630, and -800 Hounsfield units electron density; this would generate CT images for the observer study; (ii) a whole-body dosimetry verification phantom was used to ultimately estimate effective dose and risk according to the model of the BEIR VII committee. Both phantoms were scanned over a mAs range (10, 20, 30, and 40), while all other acquisition parameters remained constant. Images were reconstructed with both AIDR(3D) and FBP. For the observer study, 34 normal cases (no nodules) and 34 abnormal cases (containing 1-3 nodules, mean 1.35 ± 0.54) were chosen. Eleven observers evaluated images from all mAs and reconstruction methods under the free-response paradigm. A crossed-modality jackknife alternative free-response operating characteristic (JAFROC) analysis method was developed for data analysis, averaging data over the two factors influencing nodule detection in this study: mAs and image reconstruction (AIDR(3D) or FBP). A Bonferroni correction was applied and the threshold for declaring significance was set at 0.025 to maintain the overall probability of Type I error at α = 0.05. Contrast-to-noise (CNR) was also measured for all nodules and evaluated by a linear least squares analysis.
  
  
  RESULTS
  For random-reader fixed-case crossed-modality JAFROC analysis, there was no significant difference in nodule detection between AIDR(3D) and FBP when data were averaged over mAs [F(1, 10) = 0.08, p = 0.789]. However, when data were averaged over reconstruction methods, a significant difference was seen between multiple pairs of mAs settings [F(3, 30) = 15.96, p < 0.001]. Measurements of effective dose and effective risk showed the expected linear dependence on mAs. Nodule CNR was statistically higher for simulated nodules on images reconstructed with AIDR(3D) (p < 0.001).
  
  
  CONCLUSIONS
  No significant difference in nodule detection performance was demonstrated between images reconstructed with FBP and AIDR(3D). mAs was found to influence nodule detection, though further work is required for dose optimization.
authors.affiliation: Directorate of Radiography, University of Salford, Frederick Road Campus, Salford, Greater Manchester M6 6PU, United Kingdom and Department of Radiology, Furness General Hospital, University Hospitals of Morecambe Bay NHS Foundation Trust, Dalton Lane, Barrow-in-Furness LA14 4LF, United Kingdom.
authors.forename: J D
authors.initials: JD
authors.lastname: Thompson
authors.affiliation: Department of Radiology, University of Pittsburgh, FARP Building, Room 212, 3362 Fifth Avenue, Pittsburgh, Pennsylvania 15213.
authors.forename: D P
authors.initials: DP
authors.lastname: Chakraborty
authors.affiliation: Directorate of Radiography, University of Salford, Frederick Road Campus, Salford, Greater Manchester M6 6PU, United Kingdom.
authors.forename: K
authors.initials: K
authors.lastname: Szczepura
authors.affiliation: Directorate of Radiography, University of Salford, Frederick Road Campus, Salford, Greater Manchester M6 6PU, United Kingdom.
authors.forename: A K
authors.initials: AK
authors.lastname: Tootell
authors.affiliation: Department of Radiology, Christie Hospitals NHS Foundation Trust, 550 Wilmslow Road, Manchester M20 4BX, United Kingdom.
authors.forename: I
authors.initials: I
authors.lastname: Vamvakas
authors.affiliation: Faculty of Health and Medicine, Lancaster Medical School, Furness College, Lancaster University, Lancaster LA1 4YG, United Kingdom.
authors.forename: D J
authors.initials: DJ
authors.lastname: Manning
authors.affiliation: Directorate of Radiography, University of Salford, Frederick Road Campus, Salford, Greater Manchester M6 6PU, United Kingdom and Department of Radiography, Karolinksa Institute, Solnavägen 1, Solna 171 77, Sweden.
authors.forename: P
authors.initials: P
authors.lastname: Hogg
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D019370:Observation; D019047:Phantoms, Imaging; D013902:Radiography, Thoracic / Q000379:methods*; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods*