Gating is the synchronization of imaging with a phase of the cardiac or respiratory cycles.
A variety of means for detecting these cycles can be used, such as the ECG, peripheral pulse, chest motion, etc. The synchronization can be prospective or retrospective.

Arrhythmia rejection is a method to reject irregular RR intervals (time duration between two consecutive R waves of the electrocardiogram) in cardiac gating during cardiovascular imaging and to improve the image quality, whereby the cardiac frequency is used as the basis of the normal heart rate. The RR interval window determines the percentage variation of the heart rate. Variations of the acquired data outside the window are rejected and not used in the image reconstruction. Also one interval after the arrhythmic beat will be rejected. Arrhythmia rejection may be inappropriate for patients with certain pathologies, because if the RR interval is constant long, short, long, - all intervals would be rejected.

ECG trigger methods synchronize the heartbeat in order to minimize motion artifacts, whereat the r-wave is used as the trigger. ECG gating techniques are useful whenever data acquisition is too slow to occur during a short fraction of the cardiac cycle.

See also Triggering and Trigger Delay.

(GBPS) The gated blood pool scintigraphy is an examination to evaluate the ventricular performance. This scintigraphic blood pool imaging uses an electrocardiographic synchronizer or gating device to acquire data during repeated heart cycles at specific times in the heart cycle. Radionuclides, for example 99mTc-humanserumalbumin (HSA), are used as intravascular tracers.
GBPS allows to determinate the left ventricular function with heart minute volume, ejection fraction (EF) at rest and under exercise. Single photon emission computed tomography (SPECT) versus planar scintigraphic imaging improves cardiac evaluation due to the three dimensional nature. The GBPS method is not suitable to analyze the right ventricular function; that is best evaluated by first-pass ventriculography.
Echocardiography vs. GBPS has important disadvantages due to problems in quantitative evaluation, in patients with anatomic variations and dyskinetic left ventricles.

See also Myocardial Perfusion Imaging.

Method, which synchronize the data acquisition with the heartbeat or respiration.

See also Gating.