CT-Coronary Angiogram
CT coronary angiogram (CTA) was performed using a 64-channel CT scanner (GE Lightspeed VCT, GE Medical Systems). Reconstructed CTA images were analyzed on a dedicated 3-dimensional workstation (CardIQ Xpress, GE Medical Systems) with curved multiplanar reformation and short-axis cross-sectional viewing techniques. The mean heart rate during the scan was 64 beats/min. Calcium scoring and helical scan data was performed on all patients using prospective ECG triggering at 75% of the R-R interval. Following this, a 20ml bolus of contrast (Niopram 370®) at 6mls/sec was injected and the timing of peak contrast enhancement in the aortic arch was used to determine the timing of scan acquisition. The contrast-enhanced scan used 80mls contrast injected at 6 ml/s, followed by a 50ml at 6mls/sec saline flush, during a single expiration breath hold. The CTA scan parameters were: collimator 20 mm, slice thickness 0.625 mm; gantry rotation 350 ms; helical acquisition using a pitch of 0.16; tube current 455–515 mA with ECG tube current modulation; tube voltage range 100–140 kV; rotation time, 350 ms. The estimated radiation dose per patient was 3.3 mSv. Unobstructed coronary artery disease was defined as a quantitatively measured luminal stenosis<50%. All patients were in sinus rhythm.