Focus Session
SCMR 22nd Annual Scientific Sessions
Aravindan Kolandaivelu, MD
Assistant Professor
Johns Hopkins University School of Medicine
Mikayel Dabaghyan, PhD
MRI Physicist
Mirtle Medical Inc.
Jay Ward, BSc
Executive Vice President
Mirtle Medical Inc.
Henry Halperin, MD
Electrophysiologist
Johns Hopkins School of Medicine
Ehud Schmidt, PhD
MRI Physicist
Johns Hopkins School of Medicine
Background:
Recording ECG traces during MR imaging is important for maintaining pulse sequence timing synchronization, for arrythmia rejection, and for detecting adverse events, should they occur inside the MRI, and may be important for future correlation of abnormal ECG events with images divulging heart mechanical heart motion at those times. 12-lead ECG recording inside MRI is not currently commercially available due to gradient induced artifacts (GIVs) during imaging that can be >100 times the amplitude of the true ECG. A 12-lead MRI-compatible ECG system with real-time ECG GIV cleaning is being validated in a large cohort of severely ill patients with implanted pacemakers. Aspects of system prototypes were previously described [1-3].
Methods: With institutional IRB approval, a fourth generation (Mirtle Medical Mark4, Andover, MA) 12-lead digital ECG recording system is being utilized in patients enlisted in the Prospective Observational Study of Implantable Cardioverter‐Defibrillators (PROSE-ICD) study [4], designed to identify risk factors and enhance understanding of mechanisms that predispose to arrhythmic death in patients undergoing ICD implantation for prevention of sudden cardiac death. The ECG system consists of [Figure 1]; (A) a 10-lead MRI-safe carbon-fiber cable set, (B) a battery-operated in-room 10-channel ECG receiver, each channel utilizing a 24-bit analog-to-digital converter to record traces from 10µV to 10 Volts, at 12 KHz, spanning the GIV amplitude and frequency spectrum, (C) a PC that performs real-time digital filtering and display of GIV-removed “cleaned“ ECG traces. MRI scans focused on patients with cardiomyopathy and non-MRI-conditional ICDs: Large-Bandwidth (BW) short TR/TE (asymmetric echo) Steady State Free Precession (SSFP) and Gradient Recalled Echo (GRE) localizers, breath-hold large-BW GRE cines, breath-held Broadband-Inversion-Recovery 2D Late Gadolinium Enhancement (LGE) [5], and 3D self-navigated Ultrashort-TE radial (Cush-ball 3D-kspace trajectory) LGE [6]. ECG trace GIV-cleaning methods included down-sampling to 512 Hz, application of a Finite Impulse Response low-pass filter to 75 Hz, a 20-point median filter, followed by Gaussian filtering.
Results: The 12-lead ECG system performed robustly during the patient scans. Exemplary patient traces [Figure 2 A, 2B] demonstrate success at cleaning ECGs during GRE and SSFP scans, without fidelity loss during imaging. Normal sinus rhythm heart beats could be readily distinguished from arrhythmia beats. The multiple leads enabled seperating the sources of PVCs and unstustained Ventricular Tachycardias. Residual GIV artifacts are observed in approximately 1% of the time intervals.
Conclusion: The 12-lead MRI-compatible ECG system consistently removed MRI GIV artifacts during PROSE-ICD scans, improving patient monitoring. Performance refinement for removing artifacts during Fast Spin Echo and Echo Planar Imaging sequences is undergoing.