title: Radiation dose reduction of chest CT with iterative reconstruction in image space - Part I: studies on image quality using dual source CT.
abstract: OBJECTIVE
  To determine whether the image quality (IQ) is improved with iterative reconstruction in image space (IRIS), and whether IRIS can be used for radiation reduction in chest CT.
  
  
  METHODS
  Standard dose chest CT (SDCT) in 50 patients and low dose chest CT (LDCT) in another 50 patients were performed, using a dual-source CT, with 120 kVp and same reference mAs (50 mAs for SDCT and 25 mAs for LDCT) employed to both tubes by modifying a dual-energy scan mode. Full-dose data were obtained by combining the data from both tubes and half-dose data were separated from a single tube. These were reconstructed by using a filtered back projection (FBP) and IRIS: full-dose FBP (F-FBP); full-dose IRIS (F-IRIS); half-dose FBP (H-FBP) and half-dose IRIS (H-IRIS). Objective noise was measured. The subjective IQ was evaluated by radiologists for the followings: noise, contrast and sharpness of mediastinum and lung.
  
  
  RESULTS
  Objective noise was significantly lower in H-IRIS than in F-FBP (p < 0.01). In both SDCT and LDCT, the IQ scores were highest in F-IRIS, followed by F-FBP, H-IRIS and H-FBP, except those for sharpness of mediastinum, which tended to be higher in FBP. When comparing CT images between the same dose and different reconstruction (F-IRIS/F-FBP and H-IRIS/H-FBP) algorithms, scores tended to be higher in IRIS than in FBP, being more distinct in half-dose images. However, despite the use of IRIS, the scores were lower in H-IRIS than in F-FBP.
  
  
  CONCLUSIONS
  IRIS generally helps improve the IQ, being more distinct at the reduced radiation. However, reduced radiation by half results in IQ decrease even when using IRIS in chest CT.
authors.affiliation: Department of Radiology and Research Institute of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 138-736, Korea.
authors.forename: Hye Jeon
authors.initials: HJ
authors.lastname: Hwang
authors.forename: Joon Beom
authors.initials: JB
authors.lastname: Seo
authors.forename: Jin Seong
authors.initials: JS
authors.lastname: Lee
authors.forename: Jae-Woo
authors.initials: JW
authors.lastname: Song
authors.forename: Song Soo
authors.initials: SS
authors.lastname: Kim
authors.forename: Hyun Joo
authors.initials: HJ
authors.lastname: Lee
authors.forename: Chae Hun
authors.initials: CH
authors.lastname: Lim
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement; D013902:Radiography, Thoracic; D014057:Tomography, X-Ray Computed / Q000379:methods*; D055815:Young Adult
keywords: Chest CT; Image quality; Iterative reconstruction in image space; Radiation dose reduction