Minimizing the acquisition phase in coronary CT angiography using the second generation 320-row CT.
OBJECTIVE
We aimed to compare the radiation dose and image quality of a minimal phase window centered at 77 % compared with a wide phase window in coronary CT angiography using the second-generation 320-row CT.


METHODS
Eighty patients with heart rate ≤75 bpm were retrospectively included. The first 40 patients underwent scanning with a wide phase window (65-85 %), while the last 40 patients underwent scanning with a minimal phase window centered at 77 %. Subjective image quality was graded using a 4-point scale (4 = excellent). Image noise and contrast-to-noise ratio at the proximal segments were also analyzed. The mean effective dose was derived from the dose length product multiplied by a chest conversion coefficient (κ = 0.014 mSv mGy(-1) cm(-1)).


RESULTS
Minimal phase window scanning centered at 77 % reduced the radiation dose by 30 % compared with wide phase window scanning (1.7 vs 2.4 mSv, p = 0.0009). The subjective image quality showed no significant difference (3.75 vs 3.76, p = 0.77). No significant difference was observed in the image noise, CT number, and contrast-to-noise ratio.


CONCLUSIONS
Radiation dose could be reduced while maintaining image quality by use of a minimal phase window centered at 77 % compared with a wide phase window in coronary CT angiography using the second generation 320-row CT.
Department of Radiology, The University of Tokyo, Tokyo, Japan, tomizawa-tky@umin.ac.jp.
Nobuo
N
Tomizawa
Shigeaki
S
Kanno
Eriko
E
Maeda
Masaaki
M
Akahane
Rumiko
R
Torigoe
Kuni
K
Ohtomo
D000368:Aged; D003287:Contrast Media; D017023:Coronary Angiography / Q000379:methods*; D005260:Female; D006801:Humans; D007479:Iopamidol; D008297:Male; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*
D003287:Contrast Media; D007479:Iopamidol