Towards Low-Field fMRI: Detecting Sub-1 nT Magnetic Fields with Self-Resonance Spin-Lock Sequence

Motivation: To realize the low-field functional MRI, it is essential to improve the magnetic sensitivity of the spin-lock sequence. Goal(s): To detect less than 1 nT magnetic field in 0.3-T MRI scanner. Approach: Optimizing the conditions of the self-resonance spin-lock (SRSL) sequence, then investigating the detectable limitations varying the spin-lock frequency from 20 Hz to 100 Hz. Results: A 0.25 nT magnetic field was detected in the case of 20 Hz spin-lock frequency and 1 nT one was also detected in the other cases. These results represented the feasibility of low-field fMRI using the SRSL. Impact: We detected a 0.25 nT magnetic field in the 0.3-T low-field MRI scanner using phantom study, demonstrating the feasibility of detecting neural magnetic fields in low-field MRI scanner through the self-resonance spin-lock sequence.