Evaluation of spiral monopole antenna arrays for human brain imaging at 7 Tesla

Ultra-high field (UHF, ≥7 Tesla (T)) magnetic resonance imaging (MRI) is widely adopted for its ability to achieve high signal-to-noise ratio (SNR) for high-resolution imaging. However, the limitation of UHF is its non-uniform field distribution, which poses a challenge for clinical applications. Based on the evaluations of monopole antenna arrays (MAs), we have acquired uniform human brain images with high transmit and receive performance. However, they have limitations in terms of relatively longitudinal short coverage for human whole-brain imaging. To address this, we have developed a newly designed MA with floating shields. This design shows superior performance in terms of the extension of the longitudinal coverage. However, it still does not provide sufficient uniform images for clinical usages. Therefore, we aim to improve field uniformity by designing and fabricating monopole antennas with spiral antenna concept. In this study, we developed three types of 8-channel MAs: a conventional MA, an extended spiral monopole array (ESMA) without individual shielding, and an ESMA with individual shielding (ESMAS). Experimental evaluations confirmed the superior performance of the ESMAS producing more uniform transmit and receive profiles. High-resolution brain imaging was successfully obtained at 7 T using the ESMAS.