title: Variability of repeated coronary artery calcium scoring and radiation Dose on 64- and 16-slice computed tomography by prospective electrocardiographically-triggered axial and retrospective electrocardiographically-gated spiral computed tomography: a phantom study.
abstract: OBJECTIVE
  We sought to compare coronary artery calcium (CAC) scores, the variability and radiation doses on 64- and 16-slice computed tomography (CT) scanners by both prospective electrocardiographically (ECG)-triggered and retrospective ECG-gated scans.
  
  
  METHODS
  Coronary artery models (n = 3) with different plaque CT densities (approximately 240 Hounsfield units [HU], approximately 600 HU, and approximately 1000 HU) of four sizes (1, 3, 5, and 10 mm in length) on a cardiac phantom were scanned three times in five heart rate sequences. The tube current-time products were set to almost the same on all four protocols (32.7 mAs for 64-slice prospective and retrospective scans, 33.3 mAs for 16-slice prospective and retrospective scans). Slice thickness was set to 2.5 mm to keep the radiation dose low. Overlapping reconstruction with a 1.25-mm increment was applied on the retrospective ECG-gated scan.
  
  
  RESULTS
  The CAC scores were not different between the four protocols (one-factor analysis of variance: Agatston, P = .32; volume, P = .19; and mass, P = .09). Two-factor factorial analysis of variance test revealed that the interscan variability was different between protocols (P < .01) and scoring algorithms (P < .01). The average variability of Agatston/volume/mass scoring and effective doses were as follows: 64-slice prospective scan: 16%/15%/11% and 0.5 mSv; 64-slice retrospective scan: 11%/11%/8% and 3.7 mSv; 16-slice prospective scan: 20%/18%/13% and 0.6 mSv; and 16-slice retrospective scan: 16%/15%/11% and 2.9 to 3.5 mSv (depending on the pitch).
  
  
  CONCLUSIONS
  Retrospective ECG-gated 64-slice CT showed the lowest variability. Prospective ECG-triggered 64-slice CT, with low radiation dose, shows low variability on CAC scoring comparable to retrospective ECG-gated 16-slice CT.
authors.affiliation: Department of Clinical Radiology, Hiroshima University Hospital, Hiroshima, 734-8551, Japan. horiguch@hiroshima-u.ac.jp
authors.forename: Jun
authors.initials: J
authors.lastname: Horiguchi
authors.forename: Masao
authors.initials: M
authors.lastname: Kiguchi
authors.forename: Chikako
authors.initials: C
authors.lastname: Fujioka
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Arie
authors.forename: Yun
authors.initials: Y
authors.lastname: Shen
authors.forename: Kenichi
authors.initials: K
authors.lastname: Sunasaka
authors.forename: Toshiro
authors.initials: T
authors.lastname: Kitagawa
authors.forename: Hideya
authors.initials: H
authors.lastname: Yamamoto
authors.forename: Katsuhide
authors.initials: K
authors.lastname: Ito
mesh_terms: D002118:Calcium / Q000032:analysis*; D003331:Coronary Vessels / Q000737:chemistry*; D004562:Electrocardiography; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D002118:Calcium