Cardiac gating (MRI)
Cardiac gating or cardiac triggering refers to the gain of information about specific time points and its use for image acquisition during the cardiac cycle.
Cardiac synchronization can be achieved by the ECG signal or alternatively with a peripheral pulse transducer. The following two types of cardiac gating exist 1:
Data acquisition is carried out in a subsequent fashion after an estimation of the number of cardiac phases or segments within an R-R interval has been made.
The data acquisition is triggered by each R-wave and is stopped after the data of the estimated number of cardiac phases has been collected.
This acquisition scheme results in a small time interval of no data collection.
Imaging data is acquired in a continuous fashion throughout the whole cardiac cycle.
The data segments from the different R-R intervals are then interpolated onto an average length R-R interval which has been calculated during image reconstruction.
The advantage of this approach is that all cardiac phases are imaged.
The main disadvantage in cardiac MRI occurs in arrhythmia with large R-R interval variations.
Retrospective gating is essential for if mitral or tricuspid valve function is assessed.