Low-field fMRI using spin-lock sequences: the influence of MRI noise on magnetic field detection

Abstract

The conventional functional MRI (fMRI) has limitations for temporal resolution and static magnetic field strength, so that we focused on spin-lock sequences to overcome these limitations. We reported that a spin-locked Mz (SL-Mz) sequence could detect 2.34 nT by 0.3-T MRI, while it was reported that 80 pT was detected by 3-T MRI. We considered that the SNR of MRIs may the reason for the difference and investigated the influence of noise on magnetic field detection. We performed MRI simulation varying both noise level and amplitude of the target signal. Subsequently, we applied statistical test for MR images with and without the target magnetic field obtained by the two spin-lock sequences, i.e., SL-Mz and stimulus-induced rotary saturation (SIRS). The results showed that the SL-Mz could detect 2 nT when SNR was 1, whereas 10 nT was detected by SIRS even higher SNR of 50-100.