title: Iterative reconstruction algorithm for CT: can radiation dose be decreased while low-contrast detectability is preserved?
abstract: OBJECTIVE
  To compare the low-contrast detectability and image quality of computed tomography (CT) at different radiation dose levels reconstructed with iterative reconstruction (IR) and filtered back projection (FBP).
  
  
  METHODS
  A custom liver phantom with 12 simulated hypoattenuating tumors (diameters of 5, 10, 15, and 20 mm; tumor-to-liver contrast values of -10, -20, and -40 HU) was designed. The phantom was scanned with a standard abdominal CT protocol with a volume CT dose index of 21.6 mGy (equivalent 100% dose) and four low-dose protocols (20%, 40%, 60%, and 80% of the standard protocol dose). CT data sets were reconstructed with IR and FBP. Image noise was measured, and the tumors' contrast-to-noise ratios (CNRs) were calculated. Tumor detection was independently assessed by three radiologists who were blinded to the CT technique used. A total of 840 simulated tumors were presented to the radiologists. Statistical analyses included analysis of variance.
  
  
  RESULTS
  IR yielded an image noise reduction of 43.9%-63.9% and a CNR increase of 74.1%-180% compared with FBP at the same dose level (P < .001). The overall sensitivity for tumor detection was 64.7%-85.3% for IR and 66.3%-85.7% for FBP at the 20%-100% doses, respectively. There was no significant difference in the sensitivity for tumor detection between IR and FBP at the same dose level (P = .99). The sensitivity of the protocol at the 20% dose with FBP and IR was significantly lower than that of the protocol at the 100% dose with FBP and IR (P = .019).
  
  
  CONCLUSIONS
  As the radiation dose at CT decreases, the IR algorithm does not preserve the low-contrast detectability.
  
  
  BACKGROUND
  http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13122349/-/DC1.
authors.affiliation: Department of Medical Imaging, University Health Network, University of Toronto, Toronto, Ont, Canada; Clinic of Radiology and Nuclear Medicine, University Hospital Basel, Petersgraben 4, CH-4031 Basel, Switzerland.
authors.forename: Sebastian T
authors.initials: ST
authors.lastname: Schindera
authors.forename: Devang
authors.initials: D
authors.lastname: Odedra
authors.forename: Syed Arsalan
authors.initials: SA
authors.lastname: Raza
authors.forename: Tae Kyoung
authors.initials: TK
authors.lastname: Kim
authors.forename: Hyun-Jung
authors.initials: HJ
authors.lastname: Jang
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Szucs-Farkas
authors.forename: Patrik
authors.initials: P
authors.lastname: Rogalla
mesh_terms: D000465:Algorithms; D004867:Equipment Design; D006801:Humans; D008113:Liver Neoplasms / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*