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Design and Characterization Methodology for Efficient Wide Range Tunable MEMS Filters
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Transmit B1-field correction at 7 T using actively tuned coupled inner elements.

Hellmut Merkle1, Joseph Murphy-Boesch, Peter van Gelderen

  • 1National Institutes of Health, National Institute of Neurological Disorders and Stroke, Laboratory for Functional and Molecular Imaging, Bethesda, Maryland 20892-1065, USA.

Magnetic Resonance in Medicine
|March 26, 2011
PubMed
Summary
This summary is machine-generated.

Researchers improved magnetic resonance imaging (MRI) B(1) field homogeneity in the human head at 7 Tesla. Actively controlled loop elements locally enhance the transmit B(1) field, improving image uniformity without extra transmit channels.

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Area of Science:

  • Magnetic Resonance Imaging (MRI)
  • Radio Frequency Engineering

Background:

  • Wavelength effects in human head MRI at 7 Tesla cause intensity variations, with signal brighter centrally and darker peripherally.
  • This image nonuniformity is largely due to variations in the effective transmit B(1) field, which decreases significantly in the brain's periphery.

Purpose of the Study:

  • To explore methods for locally enhancing the transmit B(1) field in peripheral brain regions.
  • To improve B(1) field homogeneity in 7T MRI of the human head.

Main Methods:

  • Utilized actively controlled, off-resonant loop elements tuned above the NMR frequency to enhance the B(1) field locally.
  • Employed an array of eight digitally controlled elements around a custom head phantom.
  • Digitally controlled frequency offsets of the loop elements for active B(1) field control.

Main Results:

  • Demonstrated strong local enhancement of the B(1) field in targeted regions.
  • Achieved improved B(1) field homogeneity in the head phantom without requiring multiple RF transmit channels.
  • Observed some volume coil detuning due to off-resonance tuning, but sample loading remained dominant.

Conclusions:

  • Actively controlled, off-resonant loop elements are feasible for improving B(1) homogeneity in 7T head MRI.
  • This technique offers a solution for image nonuniformity without complex multi-channel transmit systems.
  • Potential for enhanced image quality and diagnostic accuracy in high-field MRI.