<p>Inhomogeneity of the transmitted radiofrequency field (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(B_1^+\)</EquationSource> </InlineEquation>) 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 <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(B_1^+\)</EquationSource> </InlineEquation> utilizing an array of high permittivity materials with switchable connections. A 3<InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\times\)</EquationSource> </InlineEquation>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 <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(B_1^+\)</EquationSource> </InlineEquation> modulation. Remote <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(B_1^+\)</EquationSource> </InlineEquation> 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 <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(B_1^+\)</EquationSource> </InlineEquation> 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<InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\%\)</EquationSource> </InlineEquation> 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<InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\%\)</EquationSource> </InlineEquation> modulation. At the relative depth of the human heart, up to 6<InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\%\)</EquationSource> </InlineEquation> of modulation was observed in the torso phantom. The presented method may provide a promising direction for cost-effective, and adaptive <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(B_1^+\)</EquationSource> </InlineEquation> shimming without changes to the scanner hardware.</p>

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Adaptive radiofrequency shimming in MRI using reconfigurable dielectric materials

  • Paulina Šiurytė,
  • Robert van de Velde,
  • Jasper van Leeuwen,
  • Kadir Berat Yildirim,
  • Ömer Can Akgün,
  • Wyger Brink,
  • Sebastian Weingärtner

摘要

Inhomogeneity of the transmitted radiofrequency field ( \(B_1^+\) ) 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 \(B_1^+\) utilizing an array of high permittivity materials with switchable connections. A 3 \(\times\) 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 \(B_1^+\) modulation. Remote \(B_1^+\) 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 \(B_1^+\) 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 \(\%\) 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 \(\%\) modulation. At the relative depth of the human heart, up to 6 \(\%\) of modulation was observed in the torso phantom. The presented method may provide a promising direction for cost-effective, and adaptive \(B_1^+\) shimming without changes to the scanner hardware.