Excitation and RF Field Control of a Human-Size 10.5-T MRI System

Patrick Bluem; Pierre-Francois Van de Moortele; Gregor Adriany; Zoya Popović

doi:10.1109/TMTT.2018.2884405

Excitation and RF Field Control of a Human-Size 10.5-T MRI System

IEEE Trans Microw Theory Tech. 2019 Mar;67(3):1184-1196. doi: 10.1109/TMTT.2018.2884405. Epub 2018 Dec 14.

Authors

Patrick Bluem¹, Pierre-Francois Van de Moortele², Gregor Adriany², Zoya Popović³

Affiliations

¹ Department of Electrical, Computer and Energy Engineering, University of Colorado, Boulder, CO 80309-0425 USA.
² Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN 55455.
³ Department of Electrical, Computer and Energy Engineering, University of Colorado, Boulder, CO 80309-0425 USA (zoya.popovic@colorado.edu).

Abstract

This paper presents an investigation of methods for improving homogeneity inside various dielectric phantoms situated in a 10.5 T human-sized MRI. The transmit B₁ ( $B_{1}^{+}$ ) field is excited with a quadrature fed circular patch-probe and a 12 element capacitively-loaded microstrip array. Both simulations and measurements show improved homogeneity in a cylindrical water phantom, an inhomogeneous phantom (pineapple), and a NIST standard phantom. The simulations are performed using a full-wave finite-difference time-domain solver (Sim4Life) in order to find the $B_{1}^{+}$ field distribution and compared to the gradient recalled echo image and efficiency result. For additional field uniformity, the wall electromagnetic boundary conditions are modified with a passive quadrifilar helix. Finally, these methods are applied in simulation to head imaging of an anatomically correct human body model (Duke, IT'IS Virtual Population) showing improved homogeneity and specific absorption rate for various excitations.

Keywords: Finite-difference time-domain (FDTD); Magnetic resonance imaging (MRI); Patch antenna; Waveguide.

Abstract

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