title: Comparison of hybrid and pure iterative reconstruction techniques with conventional filtered back projection:  dose reduction potential in the abdomen.
abstract: OBJECTIVE
  Assess the effect of filtered back projection (FBP) and hybrid (adaptive statistical iterative reconstruction [ASIR]) and pure (model-based iterative reconstruction [MBIR]) iterative reconstructions on abdominal computed tomography (CT) acquired with 75% radiation dose reduction.
  
  
  METHODS
  In an institutional review board-approved prospective study, 10 patients (mean [standard deviation] age, 60 (8) years; 4 men and 6 women) gave informed consent for acquisition of additional abdominal images on 64-slice multidetector-row CT (GE 750HD, GE Healthcare). Scanning was repeated over a 10-cm scan length at 200 and 50 milliampere second (mA s), with remaining parameters held constant at 120 kilovolt (peak), 0.984:1 pitch, and standard reconstruction kernel. Projection data were deidentified, exported, and reconstructed to obtain 4 data sets (200-mA s FBP, 50-mA s FBP, 50-mA s ASIR, 50-mA s MBIR), which were evaluated by 2 abdominal radiologists for lesions and subjective image quality. Objective noise and noise spectral density were measured for each image series.
  
  
  RESULTS
  Among the 10 patients, the maximum weight recorded was 123 kg, with maximum transverse diameter measured as 43.7 cm. Lesion conspicuity at 50-mA s MBIR was better than on 50-mA s FBP and ASIR images (P < 0.01). Image noise was rated as suboptimal on low-dose FBP and ASIR but deemed acceptable in MBIR images. Objective noise with 50-mA s MBIR was 2 to 3 folds lower compared to 50-mA s ASIR, 50-mA s FBP, and 200-mA s FBP (P < 0.0001). Noise spectral density analyses demonstrated that ASIR retains the noise spectrum signature of FBP, whereas MBIR has much lower noise with a more regularized noise spectrum pattern.
  
  
  CONCLUSIONS
  Model-based iterative reconstruction renders acceptable image quality and diagnostic confidence in 50- mA s abdominal CT images, whereas FBP and ASIR images are associated with suboptimal image quality at this radiation dose level.
authors.affiliation: Massachusetts General Hospital Imaging, Massachusetts General Hospital, Boston, MA 02114, USA. ssingh6@partners.org
authors.forename: Sarabjeet
authors.initials: S
authors.lastname: Singh
authors.forename: Mannudeep K
authors.initials: MK
authors.lastname: Kalra
authors.forename: Synho
authors.initials: S
authors.lastname: Do
authors.forename: Jean Baptiste
authors.initials: JB
authors.lastname: Thibault
authors.forename: Homer
authors.initials: H
authors.lastname: Pien
authors.forename: Owen J
authors.initials: OJ
authors.lastname: O'Connor
authors.forename: Owen O J
authors.initials: OO
authors.lastname: Connor
authors.forename: Michael A
authors.initials: MA
authors.lastname: Blake
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D011860:Radiography, Abdominal / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*