When the patient enters the magnet, the Magnetohydrodynamic Effect may cause the T-wave to increase in height. The effect is independent of the patient's ECG waveform and may be inverted by swapping the patient's head/foot first orientation on the table. Repositioning the electrodes, positioning the patient feet-first, or using another lead selection may minimize this effect.
Eliminate as many noise sources as possible, including ECG cable motion, patient movement, and breathing motion artifacts if the patient is in a head first position and the ECG cable rests on the patient’s abdomen.
To prevent ECG triggering failures, you must initiate a Gating Reset from the Gating Control window after the patient is in the magnet and has not moved for at least five seconds. This diminishes the chances of a heart rate increase (common for some people as they first enter the magnet), which may result in a reduction in the number of slices allowed per acquisition. If the patient moves during the Gating Reset process, the process fails. Do not begin the exam until you successfully complete the Gating Reset with the patient in the magnet.
Should the ECG signal degrade during data acquisition, the system automatically switches to another lead (trigger type selection) (not available in all ECG modes).
MR systems with an In-Room monitor: you can make gating selections from the Settings control panel from the Gating screen.
Do not use outdated electrodes, electrodes that have been exposed to light, or electrodes that have been left out of an air tight sealed pouch for a long time.
Do not place electrodes over bony areas such as the clavicle or sternum. Bone can interfere with signal detection.
For women with large breasts, the left breast should be raised and the red electrode placed as close to the position indicated in the ECG lead placement illustrations.
The electrodes should not be placed more than 20 to 25 cm apart.
Be sure to place the left leg (red) electrode over the apex of the heart. Place enough distance between the two electrodes (white pair and black pair) to maximize the VCGI, VCGII amplitude.
Do not press on the center portion of the electrode, but rather on the edges where the adhesive is. This can flatten the conductive gel and weaken electrical impulse detection, which may result in intermittent or missing QRS detection
Observe the waveforms during the scan. If during the acquisition you note that the signal is poor from one of the waveforms and it is no longer displaying trigger marks on that waveform, switch to the waveform that is producing the optimum signal (not available for all ECG modes).
If available, use an impedance meter to check the contact impedance of the electrode to the skin. It should be less than 2k outside of the magnet. If it exceeds 2k, then re-prep the patient and use another electrode.
All of these factors can result in noise interference with the cardiac signal during the scan.
An anterior lead placement is preferable, but if the patient’s anatomy does not allow anterior placement, try a lateral placement.
Attach the leads to the electrodes.
Verify that the white lead pair and black lead pair are orthogonal.
If the patient is oriented feet first, the leads should be routed from the chest to the head and in the center of the table. To secure the ECG cable, tape it to the pillow.
If the patient is oriented head first, the leads should be routed from the chest down the center of the patient and the table.
Make sure the connector does not lift up from the electrode once it has been attached. Rotating the connector so that it lies flat on the electrode can reduce the probability of the connector lifting off the skin. A secure connector-to-skin contact is required for a good gating signal.
Place a pillow case around the leads to prevent them from rubbing against the patient’s skin and to help reduce coil motion.
To reduce signal distortion, do not move the leads once they are positioned. Check that the leads are not in contact with the patient’s hands or feet.
Gating control screen considerations:
For Standard gating with wired configurations: If there is a problem with the LL (left leg/red) electrode or lead wire, neither ECG II nor ECG III provides a good trace. The ECG I trace is calculated from the sums of ECG II and III, therefore, the ECG I trace is also affected. It may be necessary to check the electrode and lead attachment followed by reinitializing cardiac gating.
If the waveform is not a clean trace, cycle through the leads on the Gating Control screen. Visually inspect the traces to find the best waveform. As the lead selection is changed, click Update to display the R-peak amplitude. GE strongly recommends using the default "Vector Gating" cardiac mode(s) for ECG. This the most reliable mode for ECG gating on patients, but requires a gating reset at the scan location for optimum performance. Use the combination of a visual inspection of the waveform and the R-peak amplitude to determine the best lead for gating. Performing only a visual inspection of the waveform is not sufficient because the system autoscales the waveform even if the R-peak amplitude is very low. A high R-peak amplitude in combination with a "clean" waveform ensures successful of triggers.
If the ECG waveform is inverted, select Invert on the Gating Control screen.
