title: Objective assessment of low-contrast computed tomography images with iterative reconstruction.
abstract: OBJECTIVE
  This study aims to assess low-contrast image quality using a low-contrast object specific contrast-to-noise ratio (CNRLO) analysis for iterative reconstruction (IR) computed tomography (CT) images.
  
  
  METHODS
  A phantom composed of low-contrast rods placed in a uniform material was used in this study. Images were reconstructed using filtered back projection (FBP) and IR (Adaptive Iterative Dose Reduction 3D). Scans were performed at six dose levels: 1.0, 1.8, 3.1, 4.6, 7.1 and 13.3mGy. Objective image quality was assessed by comparing CNRLO with CNR using a human observer test.
  
  
  RESULTS
  Compared with FBP, IR yielded increased CNR at the same dose levels. The results of CNRLO and observer tests showed similarities or only marginal differences between FBP and IR at the same dose levels. The coefficient of determination for CNRLO was significantly better (R(2)=0.86) than that of CNR (R(2)=0.47).
  
  
  CONCLUSIONS
  For IR, CNRLO could potentially serve as an objective index reflective of a human observer assessment. The results of CNRLO test indicated that the IR algorithm was not superior to FBP in terms of low-contrast detectability at the same radiation doses.
authors.affiliation: Department of Diagnostic Radiology, Shizuoka Cancer Centre, 1007 Shimonagakubo, Nagaizumi, Sunto, Shizuoka 411-8777, Japan. Electronic address: at.urikura@scchr.jp.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Urikura
authors.affiliation: Department of Medical Technology, Nakatsugawa Municipal General Hospital, 1522-1 Komanba, Nakatsugawa, Gifu 508-0011, Japan. Electronic address: hara_tnk2@ybb.ne.jp.
authors.forename: Takanori
authors.initials: T
authors.lastname: Hara
authors.affiliation: Division of Health Sciences, Kanazawa University Graduate of Medical Sciences, 5-11-80 Kodatsuno, Kanazawa, Ishikawa 920-0942, Japan. Electronic address: ichikawa@mhs.mp.kanazawa-u.ac.jp.
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Ichikawa
authors.affiliation: Department of Radiology, Hiroshima University Hospital, 1-2-3, Kasumi, Minami-ku, Hiroshima 734-8551, Japan. Electronic address: eiji2403@tk9.so-net.ne.jp.
authors.forename: Eiji
authors.initials: E
authors.lastname: Nishimaru
authors.affiliation: Department of Radiology, Ishinkai Yao General Hospital, 1-41 Numa, Yao, Osaka 581-0036, Japan. Electronic address: hoshi0311@hera.eonet.ne.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Hoshino
authors.affiliation: Department of Diagnostic Radiology, Shizuoka Cancer Centre, 1007 Shimonagakubo, Nagaizumi, Sunto, Shizuoka 411-8777, Japan. Electronic address: ts.yoshida@scchr.jp.
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Yoshida
authors.affiliation: Department of Diagnostic Radiology, Shizuoka Cancer Centre, 1007 Shimonagakubo, Nagaizumi, Sunto, Shizuoka 411-8777, Japan. Electronic address: y.nakaya@scchr.jp.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Nakaya
mesh_terms: D000465:Algorithms; D006801:Humans; D007091:Image Processing, Computer-Assisted; D019047:Phantoms, Imaging; D011786:Quality Control; D011829:Radiation Dosage; D059629:Signal-To-Noise Ratio; D014057:Tomography, X-Ray Computed
keywords: Computed tomography; Detectability; Image quality; Image reconstruction; Radiation dosage