title: Retrospective gating vs. prospective triggering for noninvasive coronary angiography: Assessment of image quality and radiation dose using a 256-slice CT scanner with 270 ms gantry rotation.
abstract: OBJECTIVE
  To report our clinical experience with a 256-slice multidetector computed tomography (MDCT) with a 270-ms gantry rotation system in performing CT coronary angiograms (CTCA) using both prospectively gated step and shoot (PGSS) and retrospectively gated helical (RGH) techniques.
  
  
  METHODS
  We studied 252 patients who received CTCA; 126 patients having mean heart rate (HR) of 72.1 were imaged with RGH CTCA and 126 patients having mean HR of 58.7 were imaged with PGSS CTCA. For patients with a prescan HR ≤70 beats/min, a PGSS acquisitions trigger was used, whereas patients whose prescan HR was >70 beats/min were imaged using an RGH acquisition. The blood vessel accessibility of both PGSS and RGH techniques was evaluated by grading the image quality score from 1 (no motion artifacts) to 4 (severe motion artifacts preventing diagnosis) for each coronary artery segment. Radiation doses of the techniques were also compared.
  
  
  RESULTS
  In both groups, more than 50% of segments received the best imaging score. The overall image quality scores for RGH and PGSS groups were 1.522 ± 0.317 and 1.500 ± 0.374, respectively. There was no significant difference in right coronary artery, left anterior descending artery, and left circumflex artery image quality between the two groups. Only 0.1% of segments were nonevaluative with the PGSS technique and all segments were evaluative with RGH. PGSS was associated with a 62% reduction in effective radiation dose as compared to RGH (PGSS, 5.1 mSv; RGH, 13.2 mSv).
  
  
  CONCLUSIONS
  There is no significant difference in image quality between PGSS and RGH in this study. Although providing similar image quality as RGH, PGSS was associated with a 62% reduction in effective radiation dose. Further study to confirm the diagnostic accuracy as compared to coronary artery angiography is warranted.
authors.affiliation: Department of Radiology, Shin Kong Wu Ho-Su Memorial Hospital, Taipei, Taiwan, ROC.
authors.forename: Wei-Yip
authors.initials: WY
authors.lastname: Law
authors.forename: Ching-Ching
authors.initials: CC
authors.lastname: Yang
authors.forename: Liang-Kuang
authors.initials: LK
authors.lastname: Chen
authors.forename: Tzung-Chi
authors.initials: TC
authors.lastname: Huang
authors.forename: Kun-Mu
authors.initials: KM
authors.lastname: Lu
authors.forename: Tung-Hsin
authors.initials: TH
authors.lastname: Wu
authors.forename: Greta S P
authors.initials: GS
authors.lastname: Mok
mesh_terms: D016477:Artifacts; D003287:Contrast Media; D017023:Coronary Angiography / Q000379:methods*; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging*; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement / Q000379:methods; D012189:Retrospective Studies; D015898:Tomography Scanners, X-Ray Computed; D036542:Tomography, Spiral Computed / Q000295:instrumentation* / Q000379:methods*; D014283:Triiodobenzoic Acids
chemical_list: D003287:Contrast Media; D014283:Triiodobenzoic Acids; C054871:ioversol