Contactless cardiac gating at 0.55T using high-amplitude pilot tone with interference cancellation (HAPTIC)

Purpose

To enable contactless cardiac gating at 0.55T using pilot tone (PT). Current PT methods are unable to extract weak motions, including cardiac motion, at lower B₀ field strengths (<1.5T).

Methods

We utilize high-amplitude pilot tone with interference cancellation, termed HAPTIC. The use of high amplitude PT improves sensitivity to cardiac motion, but introduces noise leakage into the imaging bandwidth. This leakage is removed using External Dynamic InTerference Estimation and Removal (EDITER) interference cancellation. HAPTIC performance at 0.55T is evaluated in healthy volunteers and patients with cardiac arrhythmia, over a 100-fold range in PT amplitude. Contactless HAPTIC gating performance is compared against conventional electrocardiogram (ECG). Noise enhancement due to HAPTIC is evaluated using noise-only scans acquired with varying PT amplitude levels.

Results

We demonstrate robust extraction of cardiac PT signals at 0.55T, with cardiac gating (ECG vs. HAPTIC) jitter <9 ms, and noise enhancement ˜12%–35%. We demonstrate the ability to track cardiac and respiratory phase during real-time MRI and demonstrate reliable separation of cardiac and respiratory phases for retrospective binning using HAPTIC. Furthermore, we demonstrate that HAPTIC provides accurate cardiac gating in the challenging case of arrhythmia to showcase initial feasibility.

Conclusion

HAPTIC enables contactless cardiac gating at 0.55T, which has not previously been demonstrated with any PT variant. This could simplify clinical workflow and could serve as a solution for mid- and low-field MRI scanners that do not include built-in physiological monitoring.