Electrocardiographic gating and monitoring in NMR imaging

ECG gating and monitoring during NMR imaging may be achieved reliably by applying the principles in this tutorial. In order to use the ECG signal both for triggering and for patient monitoring it must have a prominent R-wave, while at the same time must have little artifact from gradient switches or the Lorentz voltage across the aorta, and not be significantly distorted by gradient switching artifacts. The twin goals of no image artifacts and minimal ECG artifacts may be achieved by the following means: (1) using ECG electrodes with minimal metal, (2) selecting electrodes and cables with no ferrous metals, (3) placing the limb electrodes close together, (4) placing the line between the limb electrodes and the leg electrode parallel to the magnetic flux lines and, if possible, parallel to the transverse component of the gradient flux lines, (5) keeping the area between the limb electrodes and the leg electrode small, (6) placing that area in the center of the imager and (7) twisting or braiding the cables. Following these principles allows artifact-free images and reliable ECG monitoring during ECG-gated NMR imaging examinations.