title: A Liver Phantom Study: CT Radiation Dose Reduction and Different Image Reconstruction Algorithms Affect Diagnostic Quality.
abstract: OBJECTIVE
  The aim of this study was to evaluate whether iterative reconstruction techniques for different dose levels and/or reduction of tube potential can increase liver lesion detectability.
  
  
  METHODS
  An anthropomorphic liver phantom was scanned at different dose levels (CTDIvol 15 mGy, 7.5 mGy, 5 mGy, and 2.6 mGy) and tube potential levels (120 kV, 100 kV, and 80 kV). Images were reconstructed with the following algorithms: filtered back projection (FBP), adaptive statistical iterative reconstruction (ASiR) 40%, and a model-based iterative reconstruction (Veo). The presence or absence of lesions was assessed independently on a 4-point scale by 4 readers. The areas under the receiver operating characteristic curve were calculated.
  
  
  RESULTS
  Veo improved detectability of hyperdense liver lesions compared with both FBP and ASiR 40% at most dose levels (15 mGy, 7.5 mGy, and 5 mGy with P < 0.05). Veo also improved detectability at reduced tube potential compared with FBP (120 kV, 100 kV, and 80 kV at 5 mGy with P < 0.05) and ASiR 40% (120 kV and 100 kV at 5 mGy with P < 0.05). For ASiR 40%, the area under the receiver operating characteristic curve was significantly larger compared with FBP only at dose levels 7.5 mGy and 2.6 mGy at 120 kV. In general, the reduction of tube potential reduced the lesion detectability.
  
  
  CONCLUSIONS
  This study shows that iterative reconstruction algorithms, in particular Veo, improve lesion detectability in a liver phantom. However, a too aggressive dose reduction may result in poorer image quality. Results considering different tube potentials diverged, thus careful consideration is necessary upon tube potential reduction.
authors.affiliation: From the *Section for Radiology Radiumhospitalet, Department of Radiology and Nuclear Medicine, Oslo University Hospital, Oslo; †Department of Radiology, Ostfold Hospital Trust, Fredrikstad; ‡Institute of Physics, University of Oslo; and §The Intervention Centre, Oslo University Hospital Rikshospitalet, Oslo, Norway.
authors.forename: Kristina Ragnhild
authors.initials: KR
authors.lastname: Brænne
authors.forename: Liv Ingrid
authors.initials: LI
authors.lastname: Flinder
authors.forename: Marit
authors.initials: M
authors.lastname: Almenning Martiniussen
authors.forename: Kristin
authors.initials: K
authors.lastname: Jensen
authors.forename: Claudius Henrich
authors.initials: CH
authors.lastname: Reisse
authors.forename: Lars
authors.initials: L
authors.lastname: Julsrud
authors.forename: Anne Catrine
authors.initials: AC
authors.lastname: Martinsen
mesh_terms: D000465:Algorithms; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008099:Liver / Q000000981:diagnostic imaging*; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D000069079:Radiation Exposure / Q000032:analysis / Q000517:prevention & control*; D011835:Radiation Protection / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*