Abstract 18249: Spatially-Integrated Vectorcardiogram: An Enabling Technique for Arrhythmia Cardiac Gating in High-Field MRI
Background: Accurate QRS complex detection is essential for Cardiac MR (CMR) gating and Heart Rate (HR) monitoring. Magnetohydrodynamic voltage (VMHD) ellipses the real ECG QRS complex in high field MRI, and is severally irregular in patients with arrhythmia. This increases the difficulty of performing CMR imaging.
Objectives: Detect QRS complexes in arrhythmic ECG signals, robust to effects of MHDs in high-field MRI.
Methods: ECG data was acquired using an MRI-conditional 12-lead system from two patients diagnosed with Atrial Fibrillation (AF) both outside and in a 3T MRI . A spatially-integrated Vectorcardiogram method (siVCG) was applied for cardiac gating.
The siVCG involves synthesizing a VCG from the ECG (Fig A1-A4) using an inverse Dower transform [2-3]. The resulting VCG (Fig B1-B4) from outside the scanner was then used as a reference to estimate the heart’s principal (HPL) axis and to adapt the VCG pattern of the QRS complex. The VCG inside the MRI was projected onto the HPL axis (Fig C1-C2) to maximize the QRS complex amplitude . The HPL axis was chosen also due to its close alignment with the MRI main field (B0) for the minimized VMHD (VMHD is perpendicular to B0). The HPL axis of the projected VCG was numerically integrated along the heart’s perpendicular (HPR) axis (Fig C3). This was performed to take advantage of the large changes of the VCG signal that happen in the HPL and HPR axes simultaneously during the short duration of the QRS complex . A threshold was then applied to the result for cardiac gating (D1-D2).
Results: The siVCG maintained an improvement over the conventional VCG for cardiac gating, with each method having a percent error in these trials of 2.3% and 3.5% respectively (Fig C-D).
Conclusions: The siVCG provides a notable improvement to cardiac gating in high-field MRI over conventional VCG. Ref:  Tse, MRM, 2013  Fischer, MRM, 1999  Dower, CC, 1980
- © 2013 by American Heart Association, Inc.