A Review of Parallel Transmit Arrays for Ultra-High Field MR Imaging

Choi, C.; Webb, Andrew; Orzada, Stephan; Kelenjeridze, Mikheil; Shah, N. Jon; Felder, Jörg

doi:10.1109/rbme.2023.3244132

Cited by 9 publications

(9 citation statements)

References 218 publications

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“…5 In addition, shortening of the wavelength causes a substantial increase of local tissue heating commonly assessed by evaluating the specific absorption rate (SAR). 6,7 To overcome the RF field inhomogeneity and high local SAR issues, multi-element human head transmit (Tx) arrays consisting of a single-row (usually eight elements, i.e., 1×8 configuration) [6][7][8][9] of loops have been previously described. However, to deliver whole brain coverage, multi-row (e.g., double-row 2×8) arrays [9][10][11][12] in combination with dynamic parallel transmission 13 or static 3D RF shimming 14,15 are essential.…”

Section: Introductionmentioning

confidence: 99%

“…6,7 To overcome the RF field inhomogeneity and high local SAR issues, multi-element human head transmit (Tx) arrays consisting of a single-row (usually eight elements, i.e., 1×8 configuration) [6][7][8][9] of loops have been previously described. However, to deliver whole brain coverage, multi-row (e.g., double-row 2×8) arrays [9][10][11][12] in combination with dynamic parallel transmission 13 or static 3D RF shimming 14,15 are essential. To provide for relatively uniform current and voltage distributions along the conductor of the loop, each loop commonly caries a large number (e.g., 10 and more) of distributed high-voltage capacitors.…”

Section: Introductionmentioning

confidence: 99%

“…8 Therefore, the development of novel and more reliable UHF arrays designed to overcome issues with the B 1 + inhomogeneity and high local SAR is currently in high demand. 9 Approximately 10 years ago dipole antennas were introduced as elements of Tx-or transceiver (TxRx) RF array coils for imaging of the human body at UHF. 16 Because of the simplicity of the design, dipoles can provide a reliable and robust alternative to common surface loops.…”

Section: Introductionmentioning

confidence: 99%

“…This substantially increases complexity and, hence, may compromise the reliability and safe usage of human head Tx loop arrays 8 . Therefore, the development of novel and more reliable UHF arrays designed to overcome issues with the B 1 + inhomogeneity and high local SAR is currently in high demand 9 …”

Section: Introductionmentioning

confidence: 99%

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Evaluation of coaxial dipole antennas as transceiver elements of human head array for ultra‐high field MRI at 9.4T

Solomakha,

Bosch,

Glang

et al. 2023

Magnetic Resonance in Med

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PurposeThe aim of this work is to evaluate a new eight‐channel transceiver (TxRx) coaxial dipole array for imaging of the human head at 9.4T developed to improve specific absorption rate (SAR) performance, and provide for a more compact and robust alternative to the state‐of‐the art dipole arrays.MethodsFirst, the geometry of a single coaxial element was optimized to minimize peak SAR and sensitivity to the load variation. Next, a multi‐tissue voxel model was used to numerically simulate a TxRx array coil that consisted of eight coaxial dipoles with the optimal configuration. Finally, we compared the developed array to other human head dipole arrays. Results of numerical simulations were verified on a bench and in the scanner including in vivo measurements on a healthy volunteer.ResultsThe developed eight‐element coaxial dipole TxRx array coil showed up to 1.1times higher SAR‐efficiency than a similar in geometry folded‐end and fractionated dipole array while maintaining whole brain coverage and low sensitivity of the resonance frequency to variation in the head size.ConclusionAs a proof of concept, we developed and constructed a prototype of a 9.4T (400 MHz) human head array consisting of eight TxRx coaxial dipoles. The developed array improved SAR‐efficiency and provided for a more compact and robust alternative to the folded‐end dipole design. To the best of our knowledge, this is the first example of using coaxial dipoles for human head MRI at ultra‐high field.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Evaluation of coaxial dipole antennas as transceiver elements of human head array for ultra‐high field MRI at 9.4T

Solomakha,

Bosch,

Glang

et al. 2023

Magnetic Resonance in Med

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“…Achieving higher resolutions in MRI with higher SNR [1,2] has motivated the development of more advanced radiofrequency coils [3], stronger magnets [4][5][6] and more powerful gradient coils (higher gradient strength and higher slew rate) [7][8][9]. The interaction between the gradient coil and the magnet however puts higher demands on their design to achieve the desired performance.…”

Section: Introductionmentioning

confidence: 99%

Power deposition in the He bath induced by the Z gradient coil in the 11.7 T Iseult magnet: theory versus measurements

Aubert,

Guihard,

Dubois

et al. 2024

Supercond. Sci. Technol.

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Gradient-magnet interactions increase with higher field magnets and stronger gradient coils. Perhaps the most sensitive aspect is magnet quench, which can be induced by a loss of superconductivity of the main coil caused by a rise of the temperature of the He bath with gradient activity. Predicting power depositions thereby can be a very valuable tool to avoid dangerous frequency zones but also eventually correct design flaws. In this work, we report model predictions compared to measurements of power deposition in the He bath of the Iseult 11.7T magnet for the Z gradient coil axis.

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The possible influence of third-order shim coils on gradient–magnet interactions: an inter-field and inter-site study

Boulant,

Le Ster,

Amadon

et al. 2024

Magn Reson Mater Phy

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Objective To assess the possible influence of third-order shim coils on the behavior of the gradient field and in gradient–magnet interactions at 7 T and above. Materials and methods Gradient impulse response function measurements were performed at 5 sites spanning field strengths from 7 to 11.7 T, all of them sharing the same exact whole-body gradient coil design. Mechanical fixation and boundary conditions of the gradient coil were altered in several ways at one site to study the impact of mechanical coupling with the magnet on the field perturbations. Vibrations, power deposition in the He bath, and field dynamics were characterized at 11.7 T with the third-order shim coils connected and disconnected inside the Faraday cage. Results For the same whole-body gradient coil design, all measurements differed greatly based on the third-order shim coil configuration (connected or not). Vibrations and gradient transfer function peaks could be affected by a factor of 2 or more, depending on the resonances. Disconnecting the third-order shim coils at 11.7 T also suppressed almost completely power deposition peaks at some frequencies. Discussion Third-order shim coil configurations can have major impact in gradient–magnet interactions with consequences on potential hardware damage, magnet heating, and image quality going beyond EPI acquisitions.

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A Review of Parallel Transmit Arrays for Ultra-High Field MR Imaging

Cited by 9 publications

References 218 publications

Evaluation of coaxial dipole antennas as transceiver elements of human head array for ultra‐high field MRI at 9.4T

Evaluation of coaxial dipole antennas as transceiver elements of human head array for ultra‐high field MRI at 9.4T

Power deposition in the He bath induced by the Z gradient coil in the 11.7 T Iseult magnet: theory versus measurements

The possible influence of third-order shim coils on gradient–magnet interactions: an inter-field and inter-site study

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