title: Comparison of radiation dose and image quality: 320-MDCT versus 64-MDCT coronary angiography.
abstract: OBJECTIVE
  The purpose of this study was to compare radiation dose and image quality of 320- and 64-MDCT angiography using prospective gating.
  
  
  METHODS
  One hundred seventy-four patients underwent 320-MDCT, and 95 patients underwent 64-MDCT. The scan parameters for 320-MDCT were 120 kVp, 400 mA, and gantry rotation of 350 milliseconds; the parameters for 64-MDCT were 120 kVp, 600 mA, and gantry rotation of 350 milliseconds. Effective dose (ED) was calculated from the dose-length product and a conversion factor (k = 0.014 mSv / mGy × cm). Two observers independently assessed image quality using a 3-point scale, where 3 denotes excellent quality and 1 denotes nondiagnostic quality, using a 16-segment model. Discrepancies were settled by consensus.
  
  
  RESULTS
  The ED was significantly lower in patients undergoing 320-MDCT angiography, with a median ED of 4.4 mSv (interquartile range [IQR], 3.4-6.2 mSv), compared with 64-MDCT angiography, with a median ED of 6.2 mSv (IQR, 5.5-6.9 mSv) (p = 0.0001). In patients with a heart rate of 65 beats/min or less (92%), the median radiation dose using 320-MDCT was 4.1 mSv (IQR, 3.2-6.1 mSv), and that for 64-MDCT angiography was 6.2 mSv (IQR, 5.8-6.9 mSv) (p = 0.0001). In patients with heart rate greater than 65 beats/min (8%), the median dose was higher with 320-MDCT (8.7 mSv; IQR, 5.9-14.3 mSv) than with 64-MDCT (5.8 mSv; IQR, 5.3-6.7 mSv) (p = 0.02). Segmental image quality was significantly better for 320-MDCT (excellent or good quality, 96.66%; nondiagnostic quality, 0.1%) than for 64-MDCT angiography (excellent or good quality, 86%; nondiagnostic quality, 3.33%) (all p < 0.0001).
  
  
  CONCLUSIONS
  Image quality was good for both 320- and 64-MDCT angiography. Overall radiation dose was significantly lower in 320-MDCT angiography when the heart rate was 65 beats/min or less. Every effort should be made to control heart rate to minimize radiation dose.
authors.affiliation: Department of Radiology, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
authors.forename: Atif
authors.initials: A
authors.lastname: Khan
authors.forename: Faisal
authors.initials: F
authors.lastname: Khosa
authors.forename: Khurram
authors.initials: K
authors.lastname: Nasir
authors.forename: Aya
authors.initials: A
authors.lastname: Yassin
authors.forename: Melvin E
authors.initials: ME
authors.lastname: Clouse
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017023:Coronary Angiography / Q000379:methods*; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D011874:Radiometry; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*