EKG Detection
We often have trouble getting a clean EKG signal for cardiac gating. Any helpful hints?
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The most important factor for establishing a suitable EKG signal for gating is good contact between the skin and electrodes. This may require shaving body hair and gently abrading the skin with a special prepping gel. MRI compatible disposable electrodes are highly recommended.
Wet or sweaty skin may be blotted with a gauze pad. Do not use alcohol as it will excessively dry the skin and prevent good electrical contact. Do not reposition or reuse electrodes once placed.
It is essential the patient remain cool during the entire MRI procedure so that sweating doesn't build up under the electrodes as the study progresses. Wearing loose-fitting clothing and maintaining air flow during the scan may help.
Positioning of the electrodes is important, and for RF-safety generally a rather close configuration is advised. Investing time up front in obtaining a strong and reliable EKG tracing is well worth the effort. Some patients with congenital malformations of the heart or left ventricular infarction may need to have leads placed in otherwise unusual locations to detect an acceptable signal.
Once the patient is placed into the center of the scanner, the EKG will change due to magnetohydrodynamic effects that tend to elevate the T-wave and depress the R-wave. Several options are available at the scanner console for selecting the best EKG lead or combination of leads for triggering. Generally the lead with the highest and sharpest R-waves is chosen. Some scanners offer the option of detection using a vectorcardiographic method rather than simple EKG which increases reliability of triggering.
Occasionally EKG-triggering will simply be impossible leaving peripheral pulse gating as the only alternative. This most commonly occurs in patients with large pericardial effusions and/or emphysema where recorded EKG voltages are very small. The references below from Philips NetForum On-line Community provide additional practical tips for achieving a high success rate for EKG gating.
Wet or sweaty skin may be blotted with a gauze pad. Do not use alcohol as it will excessively dry the skin and prevent good electrical contact. Do not reposition or reuse electrodes once placed.
It is essential the patient remain cool during the entire MRI procedure so that sweating doesn't build up under the electrodes as the study progresses. Wearing loose-fitting clothing and maintaining air flow during the scan may help.
Positioning of the electrodes is important, and for RF-safety generally a rather close configuration is advised. Investing time up front in obtaining a strong and reliable EKG tracing is well worth the effort. Some patients with congenital malformations of the heart or left ventricular infarction may need to have leads placed in otherwise unusual locations to detect an acceptable signal.
Once the patient is placed into the center of the scanner, the EKG will change due to magnetohydrodynamic effects that tend to elevate the T-wave and depress the R-wave. Several options are available at the scanner console for selecting the best EKG lead or combination of leads for triggering. Generally the lead with the highest and sharpest R-waves is chosen. Some scanners offer the option of detection using a vectorcardiographic method rather than simple EKG which increases reliability of triggering.
Occasionally EKG-triggering will simply be impossible leaving peripheral pulse gating as the only alternative. This most commonly occurs in patients with large pericardial effusions and/or emphysema where recorded EKG voltages are very small. The references below from Philips NetForum On-line Community provide additional practical tips for achieving a high success rate for EKG gating.
References
Springorum R. 10 tips for routine cardiac MR. Philips NetForum Community, 2014.
de Kok W. Tips for cardiac triggering in MRI. Philips NetForum Community, 2014.
de Kok W. Tips for wireless cardiac triggering in MRI. Philips NetForum Community, 2014.
Springorum R. 10 tips for routine cardiac MR. Philips NetForum Community, 2014.
de Kok W. Tips for cardiac triggering in MRI. Philips NetForum Community, 2014.
de Kok W. Tips for wireless cardiac triggering in MRI. Philips NetForum Community, 2014.
Related Questions
Is cardiac gating the same as triggering?
I've heard the magnetic field changes the EKG. Why does this occur? It it dangerous?
Is cardiac gating the same as triggering?
I've heard the magnetic field changes the EKG. Why does this occur? It it dangerous?