How to use a prospective gated technique for cardiac CT.

A prospective, electrocardiographically gated technique was recently adapted for use with coronary and cardiac multidetector row CT studies. The most widely available form of prospective gating uses "step-and-shoot" axial data acquisition, an incrementally moving table, adaptive electrocardiographic triggering, an improved image reconstruction algorithm, and multiphase reconstruction capability. Studies have shown a 77%-87% effective radiation dose reduction compared with retrospective gating and equal to significantly improved image quality. Comparison with conventional angiography has proven it to be as accurate as retrospective gating for coronary stenosis detection. The technique is not applicable to all patients because there are some restrictions for clinical use, including a limited number of reconstructed phases and a maximum scan heart rate of 68-75 beats/min. However, with careful patient selection and effective heart rate control, prospective gating can be used in a high percentage of cardiac CT examinations. This article reviews the scanning and patient selection protocols for prospective gating and discusses how it may be used in clinical practice.