# Adaptive radiofrequency shimming in MRI using reconfigurable dielectric materials

## TL;DR

This paper introduces a new MRI technique using reconfigurable materials to improve image quality by modulating radiofrequency fields.

## Contribution

A novel adaptive radiofrequency shimming method using switchable dielectric materials is proposed for MRI.

## Key findings

- A 3×3 array of barium titanate elements with PIN diodes achieved up to 11% B₁⁺ modulation in simulations.
- Phantom experiments confirmed 11.6±0.2% B₁⁺ modulation at 15 mm depth with 5 V bias voltage.
- Modulation effects were observed up to 6% at the relative depth of the human heart in torso-shaped phantoms.

## Abstract

Inhomogeneity of the transmitted radiofrequency field (\documentclass[12pt]{minimal}
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\begin{document}$$B_1^+$$\end{document}) is a major factor hindering the image quality in Magnetic Resonance Imaging (MRI) at high field strengths. Here, a novel approach is presented, to locally modulate the \documentclass[12pt]{minimal}
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\begin{document}$$B_1^+$$\end{document} utilizing an array of high permittivity materials with switchable connections. A 3\documentclass[12pt]{minimal}
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\begin{document}$$\times$$\end{document}3 array of barium titanate suspension elements was constructed, with two PIN diode-based switchable connectors per element. Electromagnetic simulations were performed to determine configurations that produce strong \documentclass[12pt]{minimal}
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\begin{document}$$B_1^+$$\end{document} modulation. Remote \documentclass[12pt]{minimal}
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\begin{document}$$B_1^+$$\end{document} field switching was tested in a disk- and a torso-shaped phantom at 3T by applying different bias voltages to the PIN diodes. The attained \documentclass[12pt]{minimal}
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\begin{document}$$B_1^+$$\end{document} modulation was assessed at various switching pattern positions and various depths within the phantoms. The configuration with the strongest effect size has produced up to 11\documentclass[12pt]{minimal}
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\begin{document}$$\%$$\end{document} modulation in simulations at 15 mm depth, with excellent translation properties. The effects were successfully replicated in phantoms, with a 5 V bias voltage producing up to 11.6±0.2\documentclass[12pt]{minimal}
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\begin{document}$$\%$$\end{document} modulation. At the relative depth of the human heart, up to 6\documentclass[12pt]{minimal}
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\begin{document}$$\%$$\end{document} of modulation was observed in the torso phantom. The presented method may provide a promising direction for cost-effective, and adaptive \documentclass[12pt]{minimal}
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\begin{document}$$B_1^+$$\end{document} shimming without changes to the scanner hardware.