Volumetric B 1 + Field Homogenization in 7 T Brain MRI Using Metasurface Scattering

High Resolution Image Download MS PowerPoint Slide Ultrahigh field magnetic resonance imaging (UHF MRI) has enabled noninvasive human brain imaging with an excellent diagnostic accuracy. Still, when the ultrahigh-radiofrequency magnetic field of the UHF MRI encounters wavelength-scale, dissipative, and random heterogeneous materials of the brain, detrimental mesoscopic challenges arise, such as B 1 + field inhomogeneity and local heating. Here, we achieve the 3D full-volumetric field homogeneity in the 7 Tesla (T) UHF brain MRI, by proposing the metasurface design algorithm inspired by scattering theory. Starting from the electromagnetic wave scattering theory and further incorporating a pruning technique for the reduction of scattering elements, i.e., phase-controlled metasurfaces, our method systematically achieves the minimum number of participating modes for the stable volume homogenization. Applying verified full-wave numerical analysis on realistic human brain models, we repeatedly realize more than a 2-fold improvement in field homogeneity and suppressed local heating, under a clinically relevant 7 T MRI environment. The result shows a cross-disciplinary generalization of constant intensity waves in optics to microwave field homogenization in higher-Tesla MRI.