title: Value of knowledge-based iterative model reconstruction in low-kV 256-slice coronary CT angiography.
abstract: BACKGROUND
  Most current iterative reconstruction algorithms for CT imaging are a mixture of iterative reconstruction and filtered back projection. The value of "fully" iterative reconstruction in coronary CT angiography remains poorly understood.
  
  
  OBJECTIVE
  We aimed to assess the value of the knowledge-based iterative model reconstruction (IMR) algorithm on the qualitative and quantitative image quality at 256-slice cardiac CT.
  
  
  METHODS
  We enrolled 21 patients (mean age: 69 ± 11 years) who underwent retrospectively ECG gated coronary CT anhgiography at 100 kVp tube voltage. Images were reconstructed with the filtered back projection (FBP), hybrid iterative reconstruction (IR), and IMR algorithms. CT attenuation and the contrast-to-noise ratio (CNR) of the coronary arteries were calculated. With the use of a 4-point scale, 2 reviewers visually evaluated the coronary arteries and cardiac structures.
  
  
  RESULTS
  The mean CT attenuation of the proximal coronary arteries was 369.3 ± 73.6 HU, 363.9 ± 75.3 HU, and 363.3 ± 74.5 HU, respectively, for FBP, hybrid IR, and IMR and was not significantly different. The image noise of the proximal coronary arteries was significantly lower with IMR (11.3 ± 2.8 HU) than FBP (51.9 ± 12.9 HU) and hybrid IR (23.2 ± 5.2 HU). The mean CNR of the proximal coronary arteries was 9.4 ± 2.4, 20.2 ± 4.7, and 41.8 ± 9.5 with FBP, hybrid IR and IMR, respectively; it was significantly higher with IMR. The best subjective image quality for coronary vessels was obtained with IMR (proximal vessels: FBP, 2.6 ± 0.5; hybrid IR, 3.4 ± 0.5; IMR, 3.8 ± 0.4; distal vessels: FBP, 2.3 ± 0.5; hybrid IR. 3.1 ± 0.5; IMR, 3.7 ± 0.5). IMR also yielded the best visualization for cardiac systems, that is myocardium and heart valves.
  
  
  CONCLUSIONS
  The novel knowledge-based IMR algorithm yields significantly improved CNR and better subjective image quality of coronary vessels and cardiac systems with reliable CT number measurements for cardiac CT imaging.
authors.affiliation: Diagnostic Radiology, Faculty of Life Sciences, Kumamoto University, 1-1-1, Honjo, Chuo-ku, Kumamoto-shi, Kumamoto, 860-8556, Japan.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Yuki
authors.affiliation: Diagnostic Radiology, Faculty of Life Sciences, Kumamoto University, 1-1-1, Honjo, Chuo-ku, Kumamoto-shi, Kumamoto, 860-8556, Japan. Electronic address: utsunomi@kumamoto-u.ac.jp.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Utsunomiya
authors.affiliation: Medical Physics, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Funama
authors.affiliation: CT Clinical Science, Philips Electronics, Tokyo, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Tokuyasu
authors.affiliation: Diagnostic Radiology, Faculty of Life Sciences, Kumamoto University, 1-1-1, Honjo, Chuo-ku, Kumamoto-shi, Kumamoto, 860-8556, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Namimoto
authors.affiliation: Diagnostic Radiology, Faculty of Life Sciences, Kumamoto University, 1-1-1, Honjo, Chuo-ku, Kumamoto-shi, Kumamoto, 860-8556, Japan.
authors.forename: Toshinori
authors.initials: T
authors.lastname: Hirai
authors.affiliation: Diagnostic Radiology and eCardiovascular Medicine, Kumamoto Chuo Hospital, Kumamoto, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Itatani
authors.affiliation: Diagnostic Radiology and eCardiovascular Medicine, Kumamoto Chuo Hospital, Kumamoto, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Katahira
authors.affiliation: Cardiovascular Medicine, Kumamoto Chuo Hospital, Kumamoto, Japan.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Oshima
authors.affiliation: Diagnostic Radiology, Faculty of Life Sciences, Kumamoto University, 1-1-1, Honjo, Chuo-ku, Kumamoto-shi, Kumamoto, 860-8556, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Yamashita
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D055424:Cardiac-Gated Imaging Techniques / Q000379:methods*; D017023:Coronary Angiography / Q000379:methods*; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging*; D003331:Coronary Vessels / Q000000981:diagnostic imaging*; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D061330:Multidetector Computed Tomography / Q000379:methods*; D010865:Pilot Projects; D011237:Predictive Value of Tests; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D059629:Signal-To-Noise Ratio
keywords: Cardiac CT; Coronary artery; Iterative model reconstruction; Low tube voltage; Multidetector CT