title: Improvements to image quality using hybrid and model-based iterative reconstructions: a phantom study.
abstract: BACKGROUND
  The number of computed tomography (CT) examinations is increasing and leading to an increase in total patient exposure. It is therefore important to optimize CT scan imaging conditions in order to reduce the radiation dose. The introduction of iterative reconstruction methods has enabled an improvement in image quality and a reduction in radiation dose.
  
  
  OBJECTIVE
  To investigate how image quality depends on reconstruction method and to discuss patient dose reduction resulting from the use of hybrid and model-based iterative reconstruction.
  
  
  METHODS
  An image quality phantom (Catphan® 600) and an anthropomorphic torso phantom were examined on a Philips Brilliance iCT. The image quality was evaluated in terms of CT numbers, noise, noise power spectra (NPS), contrast-to-noise ratio (CNR), low-contrast resolution, and spatial resolution for different scan parameters and dose levels. The images were reconstructed using filtered back projection (FBP) and different settings of hybrid (iDose4) and model-based (IMR) iterative reconstruction methods.
  
  
  RESULTS
  iDose4decreased the noise by 15-45% compared with FBP depending on the level of iDose4. The IMR reduced the noise even further, by 60-75% compared to FBP. The results are independent of dose. The NPS showed changes in the noise distribution for different reconstruction methods. The low-contrast resolution and CNR were improved with iDose4, and the improvement was even greater with IMR.
  
  
  CONCLUSIONS
  There is great potential to reduce noise and thereby improve image quality by using hybrid or, in particular, model-based iterative reconstruction methods, or to lower radiation dose and maintain image quality.
authors.affiliation: Medical Radiation Physics, Department of Translational Medicine, Lund University, Skåne University Hospital, Malmö, Sweden Marie-Louise.Aurumskjold@skane.se.
authors.forename: Marie-Louise
authors.initials: ML
authors.lastname: Aurumskjöld
authors.affiliation: Medical Radiation Physics, Department of Translational Medicine, Lund University, Skåne University Hospital, Malmö, Sweden.
authors.forename: Kristina
authors.initials: K
authors.lastname: Ydström
authors.affiliation: Medical Radiation Physics, Department of Translational Medicine, Lund University, Skåne University Hospital, Malmö, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Tingberg
authors.affiliation: Medical Radiation Physics, Department of Translational Medicine, Lund University, Skåne University Hospital, Malmö, Sweden.
authors.forename: Marcus
authors.initials: M
authors.lastname: Söderberg
mesh_terms: D000465:Algorithms; D006801:Humans; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D000069079:Radiation Exposure / Q000032:analysis* / Q000517:prevention & control*; D011835:Radiation Protection / Q000379:methods*; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*; D060726:Torso / Q000000981:diagnostic imaging
keywords: Computed tomography (CT); dose reduction; image quality; iterative reconstruction; noise