Operating instructions

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HeartView CT
Prospective ECG Triggering Versus Ret-
rospective ECG Gating
With prospective ECG triggering, the heart volume is
covered in a "step-and-shoot" technique. The patient’s
ECG signal is used to start sequential scans with a pre-
defined offset to the R-waves of the patient’s ECG.
With retrospective ECG gating, the heart volume is cov-
ered continuously by a spiral scan. The patient’s ECG
signal is recorded simultaneously to allow a retrospec-
tive selection of the data segments used for image
reconstruction. Prospective ECG triggering has the
benefit of smaller patient dose than ECG-gated spiral
scanning, since scan data is acquired in the previously
selected heart phases only. It does not, however pro-
vide continuous volume coverage with overlapping
slices and mis-registration of anatomical details may
occur. Furthermore, reconstruction of images in differ-
ent phases of the cardiac cycle for functional evalua-
tion is not possible using Prospective Triggering tech-
nique. Since ECG triggered sequential scanning
depends on a reliable prediction of the patient’s next
RR-interval by using the mean of the preceeding RR-
intervals, the method should not be used for patients
with arrhythmia and irregular heart rates. To maintain
the benefits of ECG-gated spiral CT but reduce patient
dose, ECG-controlled dose-modulation is available.