Subwavelength dielectric waveguide for efficient travelling-wave magnetic resonance imaging

Yang Gao; Tong Liu; Tao Hong; Youtong Fang; Wen Jiang; Xiaotong Zhang

doi:10.1038/s41467-024-46638-5

Subwavelength dielectric waveguide for efficient travelling-wave magnetic resonance imaging

Nat Commun. 2024 Mar 14;15(1):2298. doi: 10.1038/s41467-024-46638-5.

Authors

Yang Gao^{1

2

3}, Tong Liu⁴, Tao Hong^{4

5}, Youtong Fang⁶, Wen Jiang^{4

5}, Xiaotong Zhang^{7

8

9

10}

Affiliations

¹ Hangzhou Institute of Technology, Xidian University, Hangzhou, China. gaoyang01@xidian.edu.cn.
² School of Electronic Engineering, National Key Laboratory of Antennas and Microwave Technology, Xidian University, Xi'an, China. gaoyang01@xidian.edu.cn.
³ College of Electrical Engineering, Zhejiang University, Hangzhou, China. gaoyang01@xidian.edu.cn.
⁴ Hangzhou Institute of Technology, Xidian University, Hangzhou, China.
⁵ School of Electronic Engineering, National Key Laboratory of Antennas and Microwave Technology, Xidian University, Xi'an, China.
⁶ College of Electrical Engineering, Zhejiang University, Hangzhou, China.
⁷ College of Electrical Engineering, Zhejiang University, Hangzhou, China. zhangxiaotong@zju.edu.cn.
⁸ Second Affiliated Hospital of Zhejiang University School of Medicine, Hangzhou, China. zhangxiaotong@zju.edu.cn.
⁹ MOE Frontier Science Center for Brain Science and Brain-machine Integration, Zhejiang University, Hangzhou, China. zhangxiaotong@zju.edu.cn.
¹⁰ Interdisciplinary Institute of Neuroscience and Technology, School of Medicine, Zhejiang University, Hangzhou, China. zhangxiaotong@zju.edu.cn.

Abstract

Magnetic resonance imaging (MRI) has diverse applications in physics, biology, and medicine. Uniform excitation of nuclei spins through circular-polarized transverse magnetic component of electromagnetic field is vital for obtaining unbiased tissue contrasts. However, achieving this in the electrically large human body poses a significant challenge, especially at ultra-high fields (UHF) with increased working frequencies (≥297 MHz). Canonical volume resonators struggle to meet this challenge, while radiative excitation methods like travelling-wave (TW) show promise but often suffer from inadequate excitation efficiency. Here, we introduce a new technique using a subwavelength dielectric waveguide insert that enhances both efficiency and homogeneity at 7 T. Through TE11-to-TM11 mode conversion, power focusing, wave impedance matching, and phase velocity matching, we achieved a 114% improvement in TW efficiency and mitigated the center-brightening effect. This fundamental advancement in TW MRI through effective wave manipulation could promote the electromagnetic design of UHF MRI systems.