Figure 1
(A) Theoretically derived 19-parameter equation for the gradient-induced voltage at each ECG Electrode (i). (B) Measured induced voltage at the Left Leg (LL) during and SSFP sequence (TR/TE=3.09/1.32ms). Magnitude is 0.7 Volts. Inset shows real ECG when MRI was not pulsing. (C) Frequency spectrum of induced-voltage on LL during SSFP sequence. Spectral peaks are at 60Hz and a harmonics of (1/TR) frequency ~320 Hz. (D) ECG traces V1-V6 recorded during a training GRE sequence (TR/TE=20/1.97ms), which consisted of intermittent imaging (Gradient ON) and non-imaging (Gradient OFF) segments. The non-imaging segment was then subtracted from the traces acquired during imaging ("corrupted ECGs", red lines), and the resulting traces fitted to the theoretical equation, in order to compute its coefficients P11- P18i and Ci. The calculated induced-voltages were then removed from the corrupted ECGs, resulting in restored ECGs (blue line) that were very similar to the true ECG. (E) Zoomed view of imaging-segment in (D), showing corrupted (red) and restored (blue lines) traces. Bottom Section showing gradient waveforms along x, y, and z directions recorded during this time. Black arrows highlight QRS complexes, which are easily observed in the restored traces. (F) during a full-resolution multi-slice SSFP sequences, the recorded ECG traces (red line) from 5 parallel slices were cleaned (blue line) in real-time using the equation, using coefficients calculated from a prior single-slice accelerated (training) sequence. (G) The 19-fit parameters for the V6 electrode for the same SSFP sequence acquired along multiple directions in a single volunteer; Coronal, 45 degrees oblique between Coronal and Sagittal, Sagittal, 45 degrees oblique between Sagittal and Transverse, Transverse.