Low-frequency magnetic signal detection using stimulus-induced rotary saturation sequence in ultra-low field MRI

Motivation: Realization of biomagnetic measurement using MRI with high spatial resolution. Goal(s): Detection of low-frequency magnetic signals below 50 Hz in ultra-low field MRI (ULF-MRI). Approach: Magnetic signal detections were performed by stimulus-induced rotary saturation (SIRS) sequence in ULF-MRI. As magnetic signals, reference magnetic fields with 225 nTpp in amplitude and 10, 15, ..., 70 Hz in frequency were applied to the bottle phantom. Results: The signal reduction of approximately 20% were observed when the reference magnetic field between 30 Hz and 45 Hz were applied. This indicates that low-frequency magnetic signals can be detected by the SIRS sequence in ULF-MRI. Impact: We demonstrate the feasibility of biomagnetic measurement below 50 Hz such as brain activity first time by realizing low-frequency magnetic signal detection using stimulus-induced rotary saturation sequence in ULF-MRI with 7 mT in B0.