Multidetector CT Cardiac Protocol:
Patient position:
The patient should be positioned so that the heart is near the center of rotation of the gantry [1]. This permits constant temporal resolution, rather than variable resolution as the x-ray tube rotates on the gantry [1].
Heart rate:
If the heart rate is too high (over 100 beats per minute) motion free cardiac imaging during diastole becomes very difficult due to the requirement for a temporal resolution of under 150 msec [1]. A heart rate of under 80 beats per minute is preferred and can be obtained with the use of beta-blocker medication prior to the exam [1].
Acquisition:
Coronary artery calcium scoring: For a 16 slice MDCT- a 16 row mode, scan from carina to cardiac apex, 25 cm FOV, 120 kV, 300-320 mAs (although other authors suggest a lower mA 50-100 [2], 1.25 mm collimation, 0.4 to 0.5 sec rotation, 20 mm table feed between each acquisition, prospective gating with a delay of 70%, reconstruction of eight images at 2.5 mm thickness per table location [1]. The approximate image acquisition time is 15-16 seconds [1].
Dosimetry:
The radiation exposure from cardiac CT is relatively high due to the requirement for continuous overlapping scans [1]. Calcium scoring exposure is between 1-2 mSv, while coronary CT angiography has a 5 to 10 mSv exposure [1].
REFERENCES:
(1) AJR 2004; Desjardins B, Kazerooni EA. ECG-gated cardiac CT. 182: 993-1010
(2) Radiol Clin N Am 2005; Chiles C, Carr JJ. Vascular diseases of the thorax: evaluation with multidetector CT. 43: 543-569
