Computed Tomography Coronary Angiography – Contrast Agent
CT coronary imaging requires intravenous administration of iodinated contrast medium. Current 64-slice CT scanner protocols recommend using 80–100ml of contrast medium injection at a rate of 4–6ml/second; therefore, CT-CA is indicated only for patients with normal renal function.

Computed Tomography Coronary Angiography – Radiation Exposure
CT-CA is associated with radiation exposure and inherent lifetime attributable risk of fatal cancer. The radiation dose for coronary CT is usually given as the effective dose (E) expressed in SI units of milli-Sievert (mSv). E represents a rough estimate of the biological risk of partial body exposure (as occurs in CT-CA) relative to an equivalent whole-body radiation exposure. Recent clinical studies revealed that 64-slice CT-CA was associated with an effective dose ranging from 13 to 15mSv for men and from 18 to 21mSv for women. This is considerably higher than the effective dose of invasive coronary angiography, which ranges from 6 to 11mSv. The radiation dose can be reduced by several techniques. Electrocardiogram (ECG)-controlled tube current modulation decreases the current of the X-ray tube during systole – CT data during systole are not used for image reconstruction; this is carried out using data during diastole – and using this technique E was reduced to 10–14mSv.¹¹ A recent study demonstrated in selected patients that by using a prospective ECG-triggered CT protocol (instead of helical scanning) the effective dose was dramatically reduced to 2.8mSv, an 83% reduction, compared with the helical CT technique.¹² It remains to be seen whether prospective CT scanning is sufficiently robust and applicable to all patients.

Table 1: Meta-analysis of the Diagnostic Accuracy of 64-slice Computed Tomography Coronary Angiography

Table 2: Diagnostic Performance of 64-slice Dual-source Computed Tomography Coronary Angiography

Table 3: Diagnostic Performance of 64-slice Dual-source Computed Tomography Coronary Angiography

Figure 1: Volume-rendered Computed Tomography Coronary Angiogram