Traveling‐wave RF shimming and parallel MRI

Brunner, David O.; Paska, Jan; Froehlich, Juerg; Pruessmann, Klaas P.

doi:10.1002/mrm.22817

Cited by 32 publications

(25 citation statements)

References 38 publications

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“…The lower B 1 + transmission efficiency of the TW excitation is due to a smaller B 1 + filling factor for the volume-of-interest. In comparison with volume resonators, the according B 1 + transmission efficiency decreases—a finding also reported by other groups [30],[31]—which constitutes the main disadvantage of the TW excitation approach. The 37% B 1 + transmission efficiency gap between both imaging approaches increases dramatically to approx.…”

Section: Discussionsupporting

confidence: 60%

The Travelling-Wave Primate System: A New Solution for Magnetic Resonance Imaging of Macaque Monkeys at 7 Tesla Ultra-High Field

Herrmann¹,

Mallow²,

Plaumann³

et al. 2015

PLoS ONE

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IntroductionNeuroimaging of macaques at ultra-high field (UHF) is usually conducted by combining a volume coil for transmit (Tx) and a phased array coil for receive (Rx) tightly enclosing the monkey’s head. Good results have been achieved using vertical or horizontal magnets with implanted or near-surface coils. An alternative and less costly approach, the travelling-wave (TW) excitation concept, may offer more flexible experimental setups on human whole-body UHF magnetic resonance imaging (MRI) systems, which are now more widely available. Goal of the study was developing and validating the TW concept for in vivo primate MRI.MethodsThe TW Primate System (TWPS) uses the radio frequency shield of the gradient system of a human whole-body 7 T MRI system as a waveguide to propagate a circularly polarized B1 field represented by the TE11 mode. This mode is excited by a specifically designed 2-port patch antenna. For receive, a customized neuroimaging monkey head receive-only coil was designed. Field simulation was used for development and evaluation. Signal-to-noise ratio (SNR) was compared with data acquired with a conventional monkey volume head coil consisting of a homogeneous transmit coil and a 12-element receive coil.ResultsThe TWPS offered good image homogeneity in the volume-of-interest Turbo spin echo images exhibited a high contrast, allowing a clear depiction of the cerebral anatomy. As a prerequisite for functional MRI, whole brain ultrafast echo planar images were successfully acquired.ConclusionThe TWPS presents a promising new approach to fMRI of macaques for research groups with access to a horizontal UHF MRI system.

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Section: Discussionsupporting

confidence: 60%

The Travelling-Wave Primate System: A New Solution for Magnetic Resonance Imaging of Macaque Monkeys at 7 Tesla Ultra-High Field

Herrmann¹,

Mallow²,

Plaumann³

et al. 2015

PLoS ONE

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“…Instead of assuming the worst possible ratio between global and maximum local SAR (Brunner et al, 2009;Collins et al, 2007), a less restrictive yet also conservative approach was adopted (Boulant et al, 2011) as presented in Appendix A.…”

Section: Specific Absorption Ratementioning

confidence: 99%

“…To facilitate our demonstration, an approach to SAR management for parallel-transmission will be presented in the next section, which while conservative, is less restrictive than the commonly adopted worst-case approach (Brunner et al, 2009;Collins et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Parallel-transmission-enabled magnetization-prepared rapid gradient-echo T1-weighted imaging of the human brain at 7T

et al. 2012

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“…For the homogeneous shim it is in the range of the power efficiency of traveling-wave MRI [49]. This is due to the fact that the integrated array's field of view is much larger than that of the local coil.…”

Section: Discussionmentioning

confidence: 99%

Analysis of an Integrated 8-Channel Tx/Rx Body Array for Use as a Body Coil in 7-Tesla MRI

et al. 2017

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Object:In this work an 8-channel array integrated into the gap between the gradient coil and bore liner of a 7-Tesla whole-body magnet is presented that would allow a workflow closer to that of systems at lower magnetic fields that have a built-in body coil; this integrated coil is compared to a local 8-channel array built from identical elements placed directly on the patient. Results: While the remote array shows a slightly better performance in terms of (B + 1 ) homogeneity, the power efficiency and the SAR efficiency are inferior to those of the local array: the transmit voltage has to be increased by a factor of 3.15 to achieve equal flip angles in a central axial slice. The g-factor calculations show a better parallel imaging g-factor for the local array. The field of view of the integrated array is larger than that of the local array. First in vivo images with the integrated array look subjectively promising. Conclusion:Although some RF performance parameters of the integrated array are inferior to a tight-fitting local array, these disadvantages might be compensated by the use of amplifiers with higher power and the use of local receive arrays. In addition, the distant placement provides the potential to include more elements in the array design.

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Traveling‐wave RF shimming and parallel MRI

Cited by 32 publications

References 38 publications

The Travelling-Wave Primate System: A New Solution for Magnetic Resonance Imaging of Macaque Monkeys at 7 Tesla Ultra-High Field

The Travelling-Wave Primate System: A New Solution for Magnetic Resonance Imaging of Macaque Monkeys at 7 Tesla Ultra-High Field

Parallel-transmission-enabled magnetization-prepared rapid gradient-echo T1-weighted imaging of the human brain at 7T

Analysis of an Integrated 8-Channel Tx/Rx Body Array for Use as a Body Coil in 7-Tesla MRI

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