title: Can use of adaptive statistical iterative reconstruction reduce radiation dose in unenhanced head CT? An analysis of qualitative and quantitative image quality.
abstract: BACKGROUND
  Iterative reconstruction can reduce image noise and thereby facilitate dose reduction.
  
  
  OBJECTIVE
  To evaluate qualitative and quantitative image quality for full dose and dose reduced head computed tomography (CT) protocols reconstructed using filtered back projection (FBP) and adaptive statistical iterative reconstruction (ASIR).
  
  
  METHODS
  Fourteen patients undergoing follow-up head CT were included. All patients underwent full dose (FD) exam and subsequent 15% dose reduced (DR) exam, reconstructed using FBP and 30% ASIR. Qualitative image quality was assessed using visual grading characteristics. Quantitative image quality was assessed using ROI measurements in cerebrospinal fluid (CSF), white matter, peripheral and central gray matter. Additionally, quantitative image quality was measured in Catphan and vendor's water phantom.
  
  
  RESULTS
  There was no significant difference in qualitative image quality between FD FBP and DR ASIR. Comparing same scan FBP versus ASIR, a noise reduction of 28.6% in CSF and between -3.7 and 3.5% in brain parenchyma was observed. Comparing FD FBP versus DR ASIR, a noise reduction of 25.7% in CSF, and -7.5 and 6.3% in brain parenchyma was observed. Image contrast increased in ASIR reconstructions. Contrast-to-noise ratio was improved in DR ASIR compared to FD FBP. In phantoms, noise reduction was in the range of 3 to 28% with image content.
  
  
  CONCLUSIONS
  There was no significant difference in qualitative image quality between full dose FBP and dose reduced ASIR. CNR improved in DR ASIR compared to FD FBP mostly due to increased contrast, not reduced noise. Therefore, we recommend using caution if reducing dose and applying ASIR to maintain image quality.
authors: The Intervention Centre, Oslo University Hospital, Postbox 4950, Nydalen, 0424 Oslo, Norway; Institute of Clinical Medicine, University of Oslo, 0027 Oslo, Norway.
authors: Bjørn Helge
authors: BH
authors: Østerås
authors: Department of Radiology and Nuclear Medicine, Oslo University Hospital, Oslo, Norway.
authors: Kristin Livelten
authors: KL
authors: Heggen
authors: Department of Radiology and Nuclear Medicine, Oslo University Hospital, Oslo, Norway.
authors: Hans Kristian
authors: HK
authors: Pedersen
authors: The Intervention Centre, Oslo University Hospital, Postbox 4950, Nydalen, 0424 Oslo, Norway.
authors: Hilde Kjernlie
authors: HK
authors: Andersen
authors: The Intervention Centre, Oslo University Hospital, Postbox 4950, Nydalen, 0424 Oslo, Norway; Institute of Physics, University of Oslo, 0027 Oslo, Norway.
authors: Anne Catrine T
authors: AC
authors: Martinsen
keywords: Computed tomography (CT); head CT; iterative reconstruction; qualitative image quality; quantitative image quality; radiation dose