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.