title: Dose reduction with iterative reconstruction in multi-detector CT: What is the impact on deformation of circular structures in phantom study?
abstract: OBJECTIVE
  To evaluate the distortion of circular structures induced by the increased image noise related to dose reduction and to assess the effect of iterative reconstruction (IR).
  
  
  METHODS
  MDCT acquisitions were performed with 120 kVp for 200/100/60/40/20mAs with 100%/50%/30%/20%/10% of dose. Raw data were reconstructed by filtered back projection (FBP) and with two IR strengths. Image quality indices referred to water and acrylic were measured on a quality image phantom. Areas, perimeters, circularity were measured on the circular inserts of 4.8, 7.9 and 11.1mm on a morphological phantom.
  
  
  RESULTS
  Dose reduction resulted in increased image noise and in decreased signal to noise ratio and contrast to noise ratio. IR improved these indices for the same dose without affecting the signal (number CT) and spatial resolution (modulation transfer function). The values of area, perimeter and circularity were altered compared to the actual value and the inserts were visually deformed with the dose reduction. IR improved these three parameters. Image quality indices, areas, perimeters and circularity of inserts were similar between the acquisition at 100% of the dose in FBP, 50% in strength-3 and 30% in strength-5 with different curves of noise power spectrum.
  
  
  CONCLUSIONS
  IR associated to 70% of dose reduction modifies the images smooth (NPS) but maintains adequate image quality indices without causing distortions of circular structures.
authors: EA 2415, Department of Radiology, Nîmes University Hospital, boulevard Professeur-Robert-Debré, 30029 Nîmes cedex, France. Electronic address: joel.greffier@chu-nimes.fr.
authors: J
authors: J
authors: Greffier
authors: EA 2415, Department of Radiology, Nîmes University Hospital, boulevard Professeur-Robert-Debré, 30029 Nîmes cedex, France.
authors: F
authors: F
authors: Macri
authors: EA 2415, Department of Radiology, Nîmes University Hospital, boulevard Professeur-Robert-Debré, 30029 Nîmes cedex, France.
authors: A
authors: A
authors: Larbi
authors: EA 2415, Department of Radiology, Nîmes University Hospital, boulevard Professeur-Robert-Debré, 30029 Nîmes cedex, France.
authors: A
authors: A
authors: Fernandez
authors: EA 2415, Department of Radiology, Nîmes University Hospital, boulevard Professeur-Robert-Debré, 30029 Nîmes cedex, France.
authors: F
authors: F
authors: Pereira
authors: EA 2415, Department of Radiology, Nîmes University Hospital, boulevard Professeur-Robert-Debré, 30029 Nîmes cedex, France; Martinos Centre for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, United States of America.
authors: C
authors: C
authors: Mekkaoui
authors: EA 2415, Department of Radiology, Nîmes University Hospital, boulevard Professeur-Robert-Debré, 30029 Nîmes cedex, France.
authors: J-P
authors: JP
authors: Beregi
mesh_terms: D007091:Image Processing, Computer-Assisted / Q000379:methods*; D061330:Multidetector Computed Tomography / Q000379:methods*; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D059629:Signal-To-Noise Ratio
keywords: Computed tomography; Deformation of circular structures; Image quality; Iterative reconstruction; Noise power spectrum