title: Prospectively versus retrospectively ECG-gated 256-slice CT angiography to assess coronary artery bypass grafts--comparison of image quality and radiation dose.
abstract: OBJECTIVE
  In this retrospective non-randomized cohort study, the image quality and radiation dose were compared between prospectively electrocardiogram (ECG)-gated axial (PGA) and retrospectively ECG-gated helical (RGH) techniques for the assessment of coronary artery bypass grafts using 256-slice CT.
  
  
  METHODS
  We studied 124 grafts with 577 segments in 64 patients with a heart rate (HR) <85 bpm who underwent CT coronary angiography (CTCA); 34 patients with RGH-CTCA and 30 patients with PGA-CTCA. The image quality of the bypass grafts was assessed by a 5-point scale (1 = excellent to 5 = non-diagnostic) for each segment (proximal anastomosis, proximal, middle, distal course of graft body, and distal anastomosis). Other objective image quality indices such as noise, signal-to-noise ratio (SNR) and contrast-to-noise ratios (CNR) were assessed. Radiation doses were also compared.
  
  
  RESULTS
  Patient characteristics of the two groups were well matched except HR. The HR of the PGA group was lower than that of the RGH group (62.0 ± 5.0 vs. 65.7 ± 7.4). For both groups, over 90% of segments received excellent or good image quality scores and none was non-evaluative. The image quality generally degraded as graft segment approached to distal anastomosis regardless of techniques and graft types. Image quality scores of the PGA group were better than those of the RGH group (1.51 ± 0.53 vs. 1.73 ± 0.62; p<0.001). There was no significantly difference of objective image quality between two techniques, and the effective radiation dose was significantly lower in the PGA group (7.0 ± 1.2 mSv) than that of the RGH group (20.0 ± 4.6 mSv) (p<0.001), with a 65.0% dose reduction.
  
  
  CONCLUSIONS
  Following bypass surgery, 256-slice PGA-CTCA is superior to RGH-CTCA in limiting the radiation dose and obtaining better image quality for bypass grafts.
authors.affiliation: Department of Biomedical Imaging and Radiological Sciences, National Yang Ming University, Taipei, Taiwan.
authors.forename: Yi-Wei
authors.initials: YW
authors.lastname: Lee
authors.forename: Ching-Ching
authors.initials: CC
authors.lastname: Yang
authors.forename: Greta S P
authors.initials: GS
authors.lastname: Mok
authors.forename: Wei-Yip
authors.initials: WY
authors.lastname: Law
authors.forename: Cheng-Tau
authors.initials: CT
authors.lastname: Su
authors.forename: Tung-Hsin
authors.initials: TH
authors.lastname: Wu
mesh_terms: D000368:Aged; D001026:Coronary Artery Bypass; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D006321:Heart / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed