Ultra-low-field Balanced Steady-state Free Precession MRI at 0.05 Tesla

Abstract

Objective: The high cost and limited accessibility of MRI scanners remain significant barriers to their broader use in clinical settings. This study aims to demonstrate the feasibility of balanced steady-state free precession (bSSFP) imaging at ultra-low-field (ULF) on a highly simplified and low-cost 0.05 Tesla whole-body MRI scanner. Methods: Experiments were conducted using a newly developed 0.05 Tesla MRI scanner that employed a permanent magnet without the need for magnetic or radiofrequency shielding. We optimized the bSSFP protocol for imaging the brain, spine, chest, abdomen, pelvis, and knee in healthy volunteers. We also examined the dependency of tissue contrast on the excitation flip angle. Results: The bSSFP protocols demonstrated reasonable image quality at 0.05 Tesla, allowing visualization of various anatomical structures. The protocols provided a spatial resolution of 2×2×6 mm³ with approximately 5 minutes of scan time per protocol. Good soft tissue contrasts were shown, facilitating the identification of major tissue types within each structure. Although bSSFP exhibited predominantly T2/T1 contrast, it could be adjusted to some extent by varying the flip angle. Conclusion: The bSSFP sequence is particularly effective for imaging at ULF due to the substantially decreased tissue T1 values. This study demonstrates that imaging various anatomical structures with bSSFP at 0.05 Tesla is efficient and feasible. Significance: Such bSSFP protocol benefits from ULF and can provide superior soft tissue contrasts compared to CT and ultrasound. This ULF bSSFP approach may offer a cost-effective alternative for imaging soft tissues in clinical settings lacking traditional MRI access.