Cardiac and respiratory motion extraction at 0.55T with high-amplitude Pilot Tone

Motivation: With Pilot Tone, it is challenging to extract weak modulations, specifically those related to cardiac motion, at lower B0 field strengths (<1.5T). Goal(s): To enable the use of cardiac Pilot Tone at low-fields (0.55T). Approach: We utilize high-amplitude pilot tone transmission in conjunction with interference mitigation to eliminate ensuing image artifacts. Results: We demonstrate robust extraction of cardiac pilot-tone signals at 0.55T. We demonstrate ability to track motion with real-time MRI, and demonstrate the ability to separate cardiac and respiratory phases with retrospective binning. Compared to ECG, the measured timing standard deviation was 36ms for Cartesian and 47ms for spiral acquisitions. Impact: This work makes it possible to extract cardiac motion from Pilot Tone at 0.55T, which was not possible before. Pilot Tone could potentially replace ECG gating, simplify the clinical workflow, and serve for scanners that do not employ ECG.