1. Background Computed tomography coronary angiography is an accurate method for the non-invasive diagnosis of coronary artery disease Eur Heart J 2005;26:1482–1487 Use of 64-detector CT coronary angiography performed with step and shoot has similar subjective image quality scores but 77% lower patient radiation dose when compared with use of retrospective ECG gating Radiology 2008;248:431–437 A systolic window for tube current modulation in subject with higher heart rates represents a reliable tool to ensure high image quality a significantly lower dose in patients undergoing routine cardiac CT Eur radiology 2010;20:1331–1336

2. Coronary Movement vs Heart rate Systolic window is not suitable with 200ms window (19/20) HR<65 good diastolic window for 100ms and 200ms (6/7) HR>65 200ms is not sufficient (12/13) HR>70 diastolic window is not better than systolic window ( 9/10) HR>80 diastolic window is disappeared (4/4)

3. Background 75 bpm was the best threshold to shift from a diastoic to a systoic reconstruction window by using the overall image quality in 64 slice dual source MDCT Recent developed 128 slice dual source MDCT has faster temporal resolution and wider detector than 64 slice dual source MDCT. It is supposed that 128 slice dual source MDCT could obtain optimal image quality during late systolic phase at much higher heart rate Eur radiology 2010;20:1331–1336

4. Diastasis (mid-diastoic) 4 Less than 70 bpm More than 70 bpm

5. Low dose CCTA 5 Table Move Table Move Table Move Radiology 2008:431 Step and shoot Retrospective ECG gating with mA modulating Acta Radiologica 2010 (revision)

6. Purpose 6  To compare image quality and radiation dose of patients who underwent dual 128 slice MDCT (Definition Flash, Siemens medical solutions, Forchheim, Germany) performed step and shoot in late systolic phase at high heart rate with those of patients who performed step and shoot in mid diastolic phase at low heart rate