A Modified Balanced Steady State Free Precession Sequence for Overhauser Magnetic Resonance Imaging

Low- and ultralow-field magnetic resonance imaging (ULF MRI) have inherently low signal-to-noise ratio (SNR) by design. Overhauser dynamic nuclear polarization (ODNP) stands out as an effective solution for continuous signal enhancement. To accelerate imaging and reduce radiofrequency (RF) power deposition-which is critical due to the high-frequency RF fields required for ODNP-efficient pulse sequences are essential. For instance, a balanced steady-state free precession (bSSFP) sequence offers high signal efficiency. However, conventional bSSFP sequences are susceptible to B₀ inhomogeneities and temporal field drifts, which can lead to banding artifacts.

In this work, we mitigated the limitations of banding artifacts by developing a modified bSSFP sequence (bSSFP180) that allows interleaved polarization and acquisition, thereby tailoring it for ODNP-enhanced ULF MRI. The unmodified and modified sequences are compared in an imaging experiment.

The proposed sequence effectively suppresses banding artifacts and demonstrates robust performance under inhomogeneous field conditions. Experimental MRI results demonstrated that bSSFP 180 achieves banding artifact-free performance.

The banding artifact-free bSSFP180 images represent a significant advancement toward the practical and reliable use of ODNP-enhanced imaging in future biomedical applications. This is particularly relevant for MRI experiments that employ lightweight, cost-efficient, permanent magnet systems in low-field environments, which often face challenges related to field instability and inhomogeneity.