Principles of cardiac dual source CT (DSCT)

Dual source CT (DSCT), which combines two arrays of X-ray tube and dectector in one gantry, provides a temporal resolution of 82.5 ms which is not dependant on the heart rate, because each of two arrays travels only 90 degrees to acquire sufficient data. Each detector has 40 detector rows (32 central rows with 0.6 mm collimated slice width and 4 other rows with 1.2 mm collimated slice width). Using the Z-flying focal spot technique, two subsequent 32-slice readings with 0.6 mm collimated slice width are combined to one 64-slice projection with a sampling distance of 0.3 mm at the isocenter. In this way, 64 overlapping 0.6 mm slices per rotation are acquired. The gantry rotation time is 330 msec in cardiac mode (1-5).

No Beta-blockade is administrated prior to the scan. After placing an 18 G-intravenous access antecubitally, four ECG leads are attached to the patients’ chest. The ECG is continuously recorded to the scan. 80 mL of iodinated contrast material (400 mgI/mL), using flow tracking set at 100 HU, plus 50 ml NaCl chaser bolus are injected at 5 mm/sec for all patients by the use of a dual-head power injector.

The scanner settings are as follows: tube voltage 120 kV and tube current 400 mA for both tubes, ECG pulsing window 30-80% of the RR-interval and slices are 0.75-mm thick with a reconstruction interval of 0.5 mm. The pitch is adapted for the lowest expected heart rate during scanning. Scan direction is craniocaudal starting above the coronary ostia and ending at the diaphragm.

Data sets are reconstructed from 30 to 80% of the cardiac cycle in 10% increments, and if necessary at every % of the R-R interval, especially at higher heart rates.

The data set with highest image quality for each coronary artery is evaluated and used for further evaluation using axial and oblique multiplanar reconstructions, curved multiplanar reconstructions, oblique maximum intensity projections, and three-dimensional volume rendering technique reconstructions.