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 language | English |
|---|---|
| Pages (from-to) | 1-10 |
| Number of pages | 10 |
| Journal | eMagRes |
| Volume | 8 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - 2019 |
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Keywords
- Dipole antennas
- High-field imaging
- MR imaging
- Multitransmit
- Sar
Cite this
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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 journal › Article › Academic › peer-review
TY - JOUR
T1 - Local sar assessment for multitransmit systems
T2 - a study on the peak local SAR value as a function of magnetic field strength
AU - Raaijmakers, Alexander J.E.
AU - Steensma, Bart R.
PY - 2019
Y1 - 2019
N2 - 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.
AB - 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.
KW - Dipole antennas
KW - High-field imaging
KW - MR imaging
KW - Multitransmit
KW - Sar
UR - http://www.scopus.com/inward/record.url?scp=85067957275&partnerID=8YFLogxK
U2 - 10.1002/9780470034590.emrstm1577
DO - 10.1002/9780470034590.emrstm1577
M3 - Article
AN - SCOPUS:85067957275
VL - 8
SP - 1
EP - 10
JO - eMagRes
JF - eMagRes
SN - 2055-6101
IS - 1
ER -