An ECG trigger module for the acquisition of cardiac MR images

In cardiac MR (Magnetic Resonance) imaging, the acquisition has to run synchronously with the heart rhythm. Triggering of the acquisition can be performed by detecting the R-peak in the ECG, but this is hampered by the large deformation of the ECG, due to the static magnetic field of the scanner. Previously developed triggers, applying linear filtering techniques, are not performing sufficiently well and therefore the authors used a combination of non-linear filtering and adaptive R-peak detection. The filtering involves the difference of the original signal and its moving median. The detection algorithm estimates the periodicity, the width and the magnitude of each peak and derives if it has to be considered an R-peak or not. It has been tuned on a set of 50 digitised ECG signals, it copes with noise, extra systoles and arrhythmic phases, it has been evaluated on an independent test set of 13 ECGs and performs remarkably better than the trigger of the MR-equipment manufacturer. A real-time implementation is currently under test.<>