Frequency Selective Surface (FSS) radiofrequency shield for low-field MRI

In this paper, we propose an inductive Frequency Selective Surface (FSS) shield for RF transceiver coils in portable low-field MRI, aiming to balance electromagnetic interference suppression and coil efficiency. A high-pass mesh cylinder is designed for a 4.3MHz solenoid in a 100mT portable scanner. Shield performance is quantified in terms of shielding effectiveness (SE) and B₁ sensitivity using analytical calculations and full-wave CST simulations. The study is further validated through bench measurements and MRI scans of a cylindrical phantom and an apple, with unshielded and copper-shielded solenoids serving as references. The results show that the FSS suppresses coupled external interference by approximately 20dB while maintaining substantially higher B₁ sensitivity than the copper shield, yielding the highest image SNR among the three configurations. These findings support inductive FSS shielding as a compact and practical approach for portable MRI, with improved gradient transparency as an additional benefit.