Recommended Rules for Contrast Injection in Cardiac CT

• Dual-injector heads are loaded with saline and iodinated contrast material.

• Iodinated agent is injected, followed by saline solution.

• Synchronization of contrast injection and data acquisition can be achieved either through a bolus tracking method or by using a separate "test bolus" acquisition.

Iodine delivery rates of around 2 g/ s (1.3 to 2) are generally recommended to achieve an intracoronary attenuation of around 250 Hounsfield units (HU) or (ideally) higher.

Injection flow rate:

Should be adapted to body weight, tube voltage, and contrast concentration.

• Recommended range of 3.0 – 6.0 ml/s.

• High flow rates are possible with proper intravenous cannulas.

• Lower flow rates may be appropriate in lower tube voltages.

Volume:

• Contrast dose equation: (Scan time + delay time +2) x flow rate

• A shorter scan acquisition time can reduce the volume.

Saline chaser:

• Pushes residual contrast out of the central venous system.

• Reduces artifacts caused by the contrast in the Subclavian or brachiocephalic vein.

• Same flow rate as the contrast.

When comparing the relative iodine enhancement between all different kVs from 70 to 150 kV with each other, it is possible to calculate the % of iodine dose saving that may be achieved with a decrease in kV while yielding the same iodine enhancement.

Test bolus acquisition

• Injection of 10 to 20 mL of contrast material delivered at the same rate as will be used during the diagnostic scan.

• The test scan comprises a maximum of 40 images started 10 s after the beginning of the contrast medium injection.

• The test bolus series can be analyzed visually or with the DynEva software.

• A region of interest (ROI) is defined in the ascending aorta for analysis. The time to peak can be read in a table after entering the delay used for image acquisition.

The bolus tracking method

• Does not require a separate injection.

• A series of low-dose monitoring scans begin shortly after the start of the injection; when the contrast density increases to a specific cutoff (usually approximately 150 HU), image acquisition is triggered.

• As with the timing bolus, the location of the monitoring slice is dependent on the specific cardiac examination.

• Contrast injection is immediately followed by a saline solution.