title: Impact of Hybrid Iterative Reconstruction on Agatston Coronary Artery Calcium Scores in Comparison to Filtered Back Projection in Native Cardiac CT.
abstract: OBJECTIVE
  To investigate whether the effects of hybrid iterative reconstruction (HIR) on coronary artery calcium (CAC) measurements using the Agatston score lead to changes in assignment of patients to cardiovascular risk groups compared to filtered back projection (FBP).
  
  
  METHODS
  68 patients (mean age 61.5 years; 48 male; 20 female) underwent prospectively ECG-gated, non-enhanced, cardiac 256-MSCT for coronary calcium scoring. Scanning parameters were as follows: Tube voltage, 120 kV; Mean tube current time-product 63.67 mAs (50 - 150 mAs); collimation, 2 × 128 × 0.625 mm. Images were reconstructed with FBP and with HIR at all levels (L1 to L7). Two independent readers measured Agatston scores of all reconstructions and assigned patients to cardiovascular risk groups. Scores of HIR and FBP reconstructions were correlated (Spearman). Interobserver agreement and variability was assessed with ĸ-statistics and Bland-Altmann-Plots.
  
  
  RESULTS
  Agatston scores of HIR reconstructions were closely correlated with FBP reconstructions (L1, R = 0.9996; L2, R = 0.9995; L3, R = 0.9991; L4, R = 0.986; L5, R = 0.9986; L6, R = 0.9987; and L7, R = 0.9986). In comparison to FBP, HIR led to reduced Agatston scores between 97 % (L1) and 87.4 % (L7) of the FBP values. Using HIR iterations L1 - L3, all patients were assigned to identical risk groups as after FPB reconstruction. In 5.4 % of patients the risk group after HIR with the maximum iteration level was different from the group after FBP reconstruction.
  
  
  CONCLUSIONS
  There was an excellent correlation of Agatston scores after HIR and FBP with identical risk group assignment at levels 1 - 3 for all patients. Hence it appears that the application of HIR in routine calcium scoring does not entail any disadvantages. Thus, future studies are needed to demonstrate whether HIR is a reliable method for reducing radiation dose in coronary calcium scoring.
authors.affiliation: University Institute for Diagnostic, Interventional and Pediatric Radiology, Inselspital - University Hospital Bern, Switzerland.
authors.forename: V C
authors.initials: VC
authors.lastname: Obmann
authors.affiliation: Institute of Diagnostic and Interventional Radiology, University of Würzburg, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Klink
authors.affiliation: University Institute for Diagnostic, Interventional and Pediatric Radiology, Inselspital - University Hospital Bern, Switzerland.
authors.forename: J T
authors.initials: JT
authors.lastname: Heverhagen
authors.affiliation: Röntgeninstitut Düsseldorf, Düsseldorf, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Stork
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Laqmani
authors.affiliation: Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Adam
authors.affiliation: Röntgeninstitut Düsseldorf, Düsseldorf, Germany.
authors.forename: P G C
authors.initials: PG
authors.lastname: Begemann
mesh_terms: D000368:Aged; D000465:Algorithms; D002114:Calcinosis / Q000000981:diagnostic imaging*; D017023:Coronary Angiography / Q000379:methods*; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D018570:Risk Assessment / Q000379:methods; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*