Volumetric B1+ field homogenization in 7 Tesla brain MRI using metasurface scattering

Abstract

Ultrahigh field magnetic resonance imaging (UHF MRI) has become an indispensable tool for human brain imaging, offering excellent diagnostic accuracy while avoiding the risks associated with invasive modalities. When the radiofrequency magnetic field of the UHF MRI encounters the multifaceted complexity of the brain, characterized by wavelength-scale, dissipative, and random heterogeneous materials, detrimental mesoscopic challenges such as B1+ field inhomogeneity and local heating arise. Here we develop the metasurface design inspired by scattering theory to achieve the volumetric field homogeneity in the UHF MRI. The method focuses on finding the scattering ansatz systematically and incorporates a pruning technique to achieve the minimum number of participating modes, which guarantees stable practical implementation. Using full-wave analysis of realistic human brain models under a 7 Tesla MRI, we demonstrate more than a twofold improvement in field homogeneity and suppressed local heating, achieving better performance than even the commercial 3 Tesla MRI. The result shows a noninvasive generalization of constant intensity waves in optics, offering a universal methodology applicable to higher Tesla MRI.

arXiv comment47 pages, 17 figures

References in corpus (5)

• Phase-only transmissive spatial light modulator based on tunable dielectric metasurface
• A convergent Born series for solving the inhomogeneous Helmholtz equation in arbitrarily large media
• Improving B1 homogeneity in abdominal imaging at 3 T with light and compact metasurface
• Heavy tails and pruning in programmable photonic circuits
• Flexible metasurface for improving brain imaging at 7T