Local sar assessment for multitransmit systems: a study on the peak local SAR value as a function of magnetic field strength

Alexander J.E. Raaijmakers, Bart R. Steensma

Research output: Contribution to journalArticleAcademicpeer-review

1 Citation (Scopus)

Abstract

With increasing permanent magnetic field strength B0, the frequency of the radiofrequency field B1 increases. The concomitantly reduced wavelength results in interference patterns that cause signal inhomogeneities and for ultrahigh field strengths even signal voids. These inhomogeneities are addressed by multitransmit systems. These systems use multiple transmit elements where the phase and amplitude of each element can be controlled to steer the B1-field. However, in this way the electric field that originates from the B1-field also changes. This may pose a safety risk in terms of localized tissue heating. To avoid potential hotspots, the local specific absorption rate (SAR) distribution needs to be determined by simulations. All concepts and methods to process simulation results are presented in this article. In addition, we use the presented methodology to investigate the relationship between the peak local SAR value and the magnetic field strength B0. For this purpose, we have simulated the birdcage body coil at 3 T and appropriately designed 16-channel dipole-loop transceiver arrays at 3, 7, 10.5, and 14 T. We demonstrate a linear increase of peak local SAR with B0 and a quadratic increase of signal-to-noise-ratio (SNR) with B0.

Original languageEnglish
Pages (from-to)1-10
Number of pages10
JournaleMagRes
Volume8
Issue number1
DOIs
Publication statusPublished - 2019

Fingerprint

Magnetic Fields
Magnetic fields
Transceivers
Signal to noise ratio
Electric fields
Signal-To-Noise Ratio
Tissue
Heating
Wavelength
Safety

Keywords

  • Dipole antennas
  • High-field imaging
  • MR imaging
  • Multitransmit
  • Sar

Cite this

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title = "Local sar assessment for multitransmit systems: a study on the peak local SAR value as a function of magnetic field strength",
abstract = "With increasing permanent magnetic field strength B0, the frequency of the radiofrequency field B1 increases. The concomitantly reduced wavelength results in interference patterns that cause signal inhomogeneities and for ultrahigh field strengths even signal voids. These inhomogeneities are addressed by multitransmit systems. These systems use multiple transmit elements where the phase and amplitude of each element can be controlled to steer the B1-field. However, in this way the electric field that originates from the B1-field also changes. This may pose a safety risk in terms of localized tissue heating. To avoid potential hotspots, the local specific absorption rate (SAR) distribution needs to be determined by simulations. All concepts and methods to process simulation results are presented in this article. In addition, we use the presented methodology to investigate the relationship between the peak local SAR value and the magnetic field strength B0. For this purpose, we have simulated the birdcage body coil at 3 T and appropriately designed 16-channel dipole-loop transceiver arrays at 3, 7, 10.5, and 14 T. We demonstrate a linear increase of peak local SAR with B0 and a quadratic increase of signal-to-noise-ratio (SNR) with B0.",
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Local sar assessment for multitransmit systems : a study on the peak local SAR value as a function of magnetic field strength. / Raaijmakers, Alexander J.E.; Steensma, Bart R.

In: eMagRes, Vol. 8, No. 1, 2019, p. 1-10.

Research output: Contribution to journalArticleAcademicpeer-review

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