Spin-lock based Magnetic Resonance Fingerprinting enables characterization of magnetic waveforms via spectral matching of rotary excitation

Motivation: Spin-lock based MRI techniques may enable direct non-invasive assessment of bioelectrical currents arising from neuronal or cardiac activity with high spatio-temporal resolution. Goal(s): This study aims to characterize the temporal evolution of ultra-low magnetic fields using a novel MR-Fingerprinting-like approach combined with the rotary excitation (REX) effect, which occurs during spin-locking. Approach: By measuring REX responses across different spin-lock frequencies and comparing them to a simulated dictionary, the temporal characteristics of various magnetic stimuli were identified in a phantom setup. Results: REX responses were matched successfully to waveform shapes with 97% accuracy, demonstrating the potential of this method for detailed magnetic field characterization. Impact: This study progresses the research and understanding of spin-lock-based magnetic field detection. Magnetic waveforms were characterized by combining concepts from Magnetic Resonance Fingerprinting and the rotary-excitation effect. This method could pave the way for in vivo characterization of biomagnetic fields.