Gradient-induced voltages on 12-lead ECGs during high duty-cycle MRI sequences and a method for their removal considering linear and concomitant gradient terms

Abstract

Purpose To restore 12-lead ECG signal fidelity inside MRI by removing magnetic-field gradient induced-voltages during high gradient-duty-cycle sequences. Theory and Methods A theoretical equation was derived, providing first- and second-order electrical fields induced at individual ECG electrode as a function of gradient fields. Experiments were performed at 3T on healthy volunteers, using a customized acquisition system which captured full amplitude and frequency response of ECGs, or a commercial recording system. The 19 equation coefficients were derived by linear regression of data from accelerated sequences, and used to compute induced-voltages in real-time during full-resolution sequences to remove ECG artifacts. Restored traces were evaluated relative to ones acquired without imaging. Results Measured induced-voltages were 0.7V peak-to-peak during balanced Steady-State Free Precession (bSSFP) with heart at the isocenter. Applying the equation during gradient echo sequencing, three-dimensional fast spin echo and multi-slice bSSFP imaging restored nonsaturated traces and second-order concomitant terms showed larger contributions in electrodes farther from the magnet isocenter. Equation coefficients are evaluated with high repeatability (ρ = 0.996) and are subject, sequence, and slice-orientation dependent. Conclusion Close agreement between theoretical and measured gradient-induced voltages allowed for real-time removal. Prospective estimation of sequence-periods where large induced-voltages occur may allow hardware removal of these signals.

A Magnetic Resonance Imaging–Conditional External Cardiac Defibrillator for Resuscitation Within the Magnetic Resonance Imaging Scanner Bore

“…Fibrillation inside the MRI scanner resulted in VF (Figure 5B), which was reversed with a single defibrillation pulse in each of the four animals studied. The Zoll Medical generator single-lead ECG display did not properly record the VF event, as it was obscured by large gradient induced voltage overlays on the ECG trace during imaging 32, 33 , but this was noted properly using the MRI-compatible hemodynamic display (Figure 5C), allowing for the timely delivery of defibrillation. This 100% success rate, although obtained from a small sample set, is equivalent to that reported for defibrillation following electrically-induced fibrillation using conventional defibrillator systems, when there is <1 min delay post-VF 28 .…”

“…This may preferably be addressed by linking the generator to an MRI-conditional ECG system 27 . We consider use of such a system a necessity, since the gradient induced voltages (GIVs) during MRI scans are of the order of volts 32 , completely masking the real ECG, so the GIVs must be removed in order to obtain reliable ECG traces 33 . This system will also serve as a reliable alarm, notifying the user of a cardiac event at an earlier stage, should it occur inside the MRI.…”

Continuous Rapid Quantification of Stroke Volume Using Magnetohydrodynamic Voltages in 3T Magnetic Resonance Imaging

“…In cases of low repetition time or where MRI pulse sequence timing/readout may be a limitation, continuous time methods of gradient removal may be employed which rely on a short training phase and knowledge of the gradient waveform and timing employed during the scan sequence 37, 38 . Further studies must be performed to investigate the feasibility of using this method in 4-lead ECG recording systems, available in the majority of MRI scanner suites and MRI-conditional ECG monitoring systems.…”

Real‐time MRI guidance of cardiac interventions

“…Unexpected hemodynamic instability is common during cardiac procedures and therefore requires invasive blood pressure and ECG tracings, which are altered by the MR environment. Improved MRI hemodynamic recording is available with the National Institutes of Health (NIH) "PRiME" system (freely available from http://nhlbi-mr.github.io/PRiME/) and 12-lead ECG systems are also under development by researchers 98 and industry (PinMed, Pittsburgh, PA).…”