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» MRI Safety

Exposures, limits, safe systems of work. This section explores safety issues in magnetic resonance imaging.

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Non-Diagnostic ECG

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Why can the ECG be misleading when a patient is in the scanner? In what way is it misleading?

ECG signals are used in cardiac triggering, and only the leads and electrodes supplied by the manufacturer of the MR system should be used. The RF and gradient fields interact with the ECG leads, and the patient's aortic blood flow through the static field (the magnetohydrodynamic effect), producing several unpredictable artefacts in the ECG trace, and so the ECG should not be used as a diagnostic tool.

Manufacturers of patient monitoring equipment are now filtering ECG traces according to the type of MRI scan being used (in particular, with respect to the magnetic field gradients used). This "repairs" the trace somewhat, though it is still essentially non-diagnostic.

Further reading on this topic:
Books: MHRA Guidelines p93, Q&A in MRI p303
Online:, Kanal

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