Introduction of the snake antenna array: Geometry optimization of a sinusoidal dipole antenna for 10.5T body imaging with lower peak SAR

Steensma, Bart R.; Moortele, Pierre-François Van de; Erturk, M. Arcan; Grant, Andrea; Adriany, Gregor; Luijten, Peter R.; Klomp, Dennis W. J.; Berg, Nico van den; Metzger, Gregory J.; Raaijmakers, Alexander J. E.

doi:10.1002/mrm.28297

Cited by 26 publications

(29 citation statements)

References 42 publications

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“…Recently a passive feeding network and a snake type antenna structure were suggested to reduce peak 10 g SAR by Zivkovic et al [ 50 ] and Steensma et al [ 51 ], respectively. In future work, we will evaluate and compare SAR and SAR efficiency as a transceiver with these newly suggested techniques and we will also extend the comparison towards transmit-only and receive-only (TORO) arrays [ 52 ].…”

Section: Discussionmentioning

confidence: 99%

Comparison of 16-Channel Asymmetric Sleeve Antenna and Dipole Antenna Transceiver Arrays at 10.5 Tesla MRI

Woo

DelaBarre

Waks

et al. 2021

IEEE Trans. Med. Imaging

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Multi-element transmit arrays with low peak 10 g specific absorption rate (SAR) and high SAR efficiency (defined as are essential for ultra-high field (UHF) magnetic resonance imaging (MRI) applications. Recently, the adaptation of dipole antennas used as MRI coil elements in multi-channel arrays has provided the community with a technological solution capable of producing uniform images and low SAR efficiency at these high field strengths. However, human head-sized arrays consisting of dipole elements have a practical limitation to the number of channels that can be used due to radiofrequency (RF) coupling between the antenna elements, as well as, the coaxial cables necessary to connect them. Here we suggest an asymmetric sleeve antenna as an alternative to the dipole antenna. When used in an array as MRI coil elements, the asymmetric sleeve antenna can generate reduced peak 10 g SAR and improved SAR efficiency. To demonstrate the advantages of an array consisting of our suggested design, we compared various performance metrics produced by 16-channel arrays of asymmetric sleeve antennas and dipole antennas with the same dimensions. Comparison data were produced on a phantom in electromagnetic (EM) simulations and verified with experiments at 10.5 Tesla (T). The results produced by the 16-channel asymmetric sleeve antenna array demonstrated 28 % lower peak 10 g SAR and 18.6 % higher SAR efficiency when compared to the 16-channel dipole antenna array.

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Section: Discussionmentioning

confidence: 99%

Comparison of 16-Channel Asymmetric Sleeve Antenna and Dipole Antenna Transceiver Arrays at 10.5 Tesla MRI

Woo

DelaBarre

Waks

et al. 2021

IEEE Trans. Med. Imaging

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“…The RF coil is crucial for patient safety and optimal image quality. Therefore, it will be interesting to observe in future studies how promising new coil concepts which have been tested successfully in large [53,54] and in other pilot studies [55][56][57][58] will further improve the image quality in clinical imaging. Additionally, the use of automated segmentation methods based on transfer learning might add to the application of CMR at 7T [59,60].…”

Section: Plos Onementioning

confidence: 99%

On the way to routine cardiac MRI at 7 Tesla - a pilot study on consecutive 84 examinations

et al. 2021

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Introduction Cardiac magnetic resonance (CMR) at ultrahigh field (UHF) offers the potential of high resolution and fast image acquisition. Both technical and physiological challenges associated with CMR at 7T require specific hardware and pulse sequences. This study aimed to assess the current status and existing, publicly available technology regarding the potential of a clinical application of 7T CMR. Methods Using a 7T MRI scanner and a commercially available radiofrequency coil, a total of 84 CMR examinations on 72 healthy volunteers (32 males, age 19–70 years, weight 50–103 kg) were obtained. Both electrocardiographic and acoustic triggering were employed. The data were analyzed regarding the diagnostic image quality and the influence of patient and hardware dependent factors. 50 complete short axis stacks and 35 four chamber CINE views were used for left ventricular (LV) and right ventricular (RV), mono-planar LV function, and RV fractional area change (FAC). Twenty-seven data sets included aortic flow measurements that were used to calculate stroke volumes. Subjective acceptance was obtained from all volunteers with a standardized questionnaire. Results Functional analysis showed good functions of LV (mean EF 56%), RV (mean EF 59%) and RV FAC (mean FAC 52%). Flow measurements showed congruent results with both ECG and ACT triggering. No significant influence of experimental parameters on the image quality of the LV was detected. Small fractions of 5.4% of LV and 2.5% of RV segments showed a non-diagnostic image quality. The nominal flip angle significantly influenced the RV image quality. Conclusion The results demonstrate that already now a commercially available 7T MRI system, without major methods developments, allows for a solid morphological and functional analysis similar to the clinically established CMR routine approach. This opens the door towards combing routine CMR in patients with development of advanced 7T technology.

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“…Nevertheless, it is shown that multichannel transmit arrays (TxArrays) with improved RF performance can be used to alleviate both issues when optimal excitation strategies are used. 9,10 In the literature, various types of the transmitting elements, such as loop coils, [11][12][13][14][15][16] transmission lines, 6,9,[17][18][19] and dipole-like structures, [20][21][22][23][24][25][26] are investigated for UHF-MRI. Thalhammer et al 11 used TxArray of loop coils for cardiac imaging at 7T.…”

Section: Introductionmentioning

confidence: 99%

“…Raaijmaker et al 20,21 introduced single-side adapted and fractionated dipole as new transmitter elements for body imaging at 7T. Steensma et al 22,23 improved the SAR performance of the dipoles at 7T and 10.5T by introducing the snake antenna. Vaughan et al 6 used a TEM coil for the head imaging at 9.4T.…”

Section: Introductionmentioning

confidence: 99%

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Improving radiofrequency power and specific absorption rate management with bumped transmit elements in ultra‐high field MRI

Sadeghi‐Tarakameh

Adriany

Metzger

et al. 2020

Magnetic Resonance in Med

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Purpose In this study, we investigate a strategy to reduce the local specific absorption rate (SAR) while keeping B1+ constant inside the region of interest (ROI) at the ultra‐high field (B0 ≥ 7T) MRI. Methods Locally raising the resonance structure under the discontinuity (i.e., creating a bump) increases the distance between the accumulated charges and the tissue. As a result, it reduces the electric field and local SAR generated by these charges inside the tissue. The B1+ at a point that is sufficiently far from the coil, however, is not affected by this modification. In this study, three different resonant elements (i.e., loop coil, snake antenna, and fractionated dipole [FD]) are investigated. For experimental validation, a bumped FD is further investigated at 10.5T. After the validation, the transmit performances of eight‐channel arrays of each element are compared through electromagnetic (EM) simulations. Results Introducing a bump reduced the peak 10g‐averaged SAR by 21, 26, 23% for the loop and snake antenna at 7T, and FD at 10.5T, respectively. In addition, eight‐channel bumped FD array at 10.5T had a 27% lower peak 10g‐averaged SAR in a realistic human body simulation (i.e., prostate imaging) compared to an eight‐channel FD array. Conclusion In this study, we investigated a simple design strategy based on adding bumps to a resonant element to reduce the local SAR while maintaining B1+ inside an ROI. As an example, we modified an FD and performed EM simulations and phantom experiments with a 10.5T scanner. Results show that the peak 10g‐averaged SAR can be reduced more than 25%.

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Introduction of the snake antenna array: Geometry optimization of a sinusoidal dipole antenna for 10.5T body imaging with lower peak SAR

Abstract: This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Cited by 26 publications

References 42 publications

Comparison of 16-Channel Asymmetric Sleeve Antenna and Dipole Antenna Transceiver Arrays at 10.5 Tesla MRI

Comparison of 16-Channel Asymmetric Sleeve Antenna and Dipole Antenna Transceiver Arrays at 10.5 Tesla MRI

On the way to routine cardiac MRI at 7 Tesla - a pilot study on consecutive 84 examinations

Improving radiofrequency power and specific absorption rate management with bumped transmit elements in ultra‐high field MRI

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