Fetus MRI at 7 T: ${B}_{1}$ Shimming Strategy and SAR Safety Implications

Fetus magnetic resonance imaging (MRI) has been rapidly developed at high fields due to its particular advantages in demonstrating pathology of the brain, lungs, complex syndromes, and conditions associated with reduction of amniotic fluid. Research regarding the safety of fetus MRI at 1.5 and 3 T has been reported, however, it has not been explored at 7 T. In this study, the B₁ shimming strategy for fetus MRI at 7 T was studied with the simultaneous constraints of the partial-body specific absorption rate (SAR) and maximum local SAR in normal controlled mode, using a pregnant-woman electromagnetic model established through the combination of real female pelvis data with numerical fetus model data. The RF field homogeneity was evaluated using the optimized strategy. The tradeoff between B₁⁺ homogeneity and SAR constraints in fetus MRI at 7 T was suggested. This research can be guidance for future clinical applications of fetus MRI at 7 T.