## Pages

### Retrospective ECG-gated spiral scanning

•  For "retrospectively ECG-gated spiral scanning" a continuous spiral scan is acquired with the ECG-signal recorded simultaneously.
•  The acquired scan data is selected for image reconstruction with respect to a pre-defined cardiac phase.
•  Similar to ECG-triggered sequential scanning a certain R-wave delay time defines the start point of data that is used for image reconstruction.
•  It has several advantages over ECG-triggered sequential scanning as the continuous acquisition allows for reconstruction of overlapping slices. But due to the retrospective analysis of the ECG, the technique is less sensitive to arrhythmia.

### Prospective ECG-triggered sequential scanning

• Cardiac CT applications require the synchronization of data acquisition to the cardiac cycle, i.e. to the movement of the heart.
• For sequential imaging, a prospective trigger is derived from the ECG-trace to initiate the CT-scan with a certain delay time after the R-wave.
• The true delay time is calculated from a given phase parameter (e.g. a percentage of the RR-interval time) for each cardiac cycle individually based on a prospective estimation of the RR-intervals.
• Usually, the delay is defined such that the scans are acquired during the diastolic phase of the heart.