Double‐row 16‐element folded‐end dipole transceiver array for 3D RF shimming of the whole human brain at 9.4 T

Nikulin, A. V.; Bosch, Daniel; Solomakha, Georgiy; Glang, Felix; Scheffler, Klaus; Avdievich, NI

doi:10.1002/nbm.4981

Cited by 4 publications

(4 citation statements)

References 32 publications

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“…The number of TxRx dipole elements can be further increased to 16 as demonstrated previously. 46 Furthermore, the array can be further optimized by increasing the number of Rx-elements. For example, this can be done by combining coaxial TxRx-dipoles with Rx-only loops as previously suggested.…”

Section: Discussionmentioning

confidence: 99%

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: Discussionmentioning

confidence: 99%

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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“…Therefore, the element count can be further raised by introducing additional rows or increasing the number of reconfigurable dipole elements in each row. Previously, we showed that a UHF double‐row dipole array for human head imaging can be constructed and properly decoupled 12,27 . Further increasing the number of rows may provide coverage of both the head and neck.…”

Section: Discussionmentioning

confidence: 99%

“…In contrast, in dipole arrays, the ends of the individual antennas always carry strong conservative electric field. Therefore, to deal with this issue, cables are commonly moved away and positioned between the dipoles at the maximum possible distance from them 10,20,27–30 . Often, several cable traps are placed along the cables 27,28,30 .…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, to deal with this issue, cables are commonly moved away and positioned between the dipoles at the maximum possible distance from them 10,20,27–30 . Often, several cable traps are placed along the cables 27,28,30 . Similarly, in the first eight‐element dipole array prototype, the DC wires were placed distantly from the dipoles 20 .…”

Section: Introductionmentioning

confidence: 99%

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Dynamic parallel imaging at 9.4 T using reconfigurable receive coaxial dipoles

Solomakha,

Glang,

Bosch

et al. 2024

NMR in Biomedicine

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Parallel imaging is one of the key MRI technologies that allow reduction of image acquisition time. However, the parallel imaging reconstruction commonly leads to a signal‐to‐noise ratio (SNR) drop evaluated using a so‐called geometrical factor (g‐factor). The g‐factor is minimized by increasing the number of array elements and their spatial diversity. At the same time, increasing the element count requires a decrease in their size. This may lead to insufficient coil loading, an increase in the relative noise contribution from the RF coil itself, and hence SNR reduction. Previously, instead of increasing the channel number, we introduced the concept of electronically switchable time‐varying sensitivities, which was shown to improve parallel imaging performance. In this approach, each reconfigurable receive element supports two spatially distinct sensitivity profiles. In this work, we developed and evaluated a novel eight‐element human head receive‐only reconfigurable coaxial dipole array for human head imaging at 9.4 T. In contrast to the previously reported reconfigurable dipole array, the new design does not include direct current (DC) control wires connected directly to the dipoles. The coaxial cable itself is used to deliver DC voltage to the PIN diodes located at the ends of the antennas. Thus, the novel reconfigurable coaxial dipole design opens a way to scale the dynamic parallel imaging up to a realistic number of channels, that is, 32 and above. The novel array was optimized and tested experimentally, including in vivo studies. It was found that dynamic sensitivity switching provided an 8% lower mean and 33% lower maximum g‐factor (for Ry × Rz = 2 × 2 acceleration) compared with conventional static sensitivities.

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RF shimming in the cervical spinal cord at 7 T

Papp,

Gilbert,

Cereza

et al. 2024

Magnetic Resonance in Med

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PurposeAdvancing the development of 7 T MRI for spinal cord imaging is crucial for the enhanced diagnosis and monitoring of various neurodegenerative diseases and traumas. However, a significant challenge at this field strength is the transmit field inhomogeneity. Such inhomogeneity is particularly problematic for imaging the small, deep anatomical structures of the cervical spinal cord, as it can cause uneven signal intensity and elevate the local specific absorption ratio, compromising image quality. This multisite study explores several RF shimming techniques in the cervical spinal cord.MethodsData were collected from 5 participants between two 7 T sites with a custom 8Tx/20Rx parallel transmission coil. We explored two radiofrequency (RF) shimming approaches from an MRI vendor and four from an open‐source toolbox, showcasing their ability to enhance transmit field and signal homogeneity along the cervical spinal cord.ResultsThe circularly polarized (CP), coefficient of variation (CoV), and specific absorption rate (SAR) efficiency shim modes showed the highest B1+ efficiency, and the vendor‐based “patient” and “volume” modes showed the lowest B1+ efficiency. The coefficient of variation method produced the highest CSF/spinal cord contrast on T2*‐weighted scans (ratio of 1.27 ± 0.03), and the lowest variation of that contrast along the superior–inferior axis.ConclusionThe study's findings highlight the potential of RF shimming to advance 7 T MRI's clinical utility for central nervous system imaging by enabling more homogenous and efficient spinal cord imaging. Additionally, the research incorporates a reproducible Jupyter Notebook, enhancing the study's transparency and facilitating peer verification.

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Double‐row 16‐element folded‐end dipole transceiver array for 3D RF shimming of the whole human brain at 9.4 T

Cited by 4 publications

References 32 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

Dynamic parallel imaging at 9.4 T using reconfigurable receive coaxial dipoles

RF shimming in the cervical spinal cord at 7 T

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