Self-decoupled radiofrequency coils for magnetic resonance imaging

Yan, Xinqiang; Gore, John C.; Grissom, William A.

doi:10.1038/s41467-018-05585-8

Cited by 69 publications

(75 citation statements)

References 45 publications

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“…Recently, a novel approach for decoupling of loop antennas was suggested which uses the property of a Huygens element to create a null of the electromagnetic field in the near zone [7]. In this coils, a lumped capacitor is located at a top point of the loop (which is opposite to the feeding point).…”

Section: Introductionmentioning

confidence: 99%

Analysis of High Impedance Coils Both in Transmission and Reception Regimes

et al. 2020

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Theory of a high impedance coil (HIC)-a cable loop antenna with a modified shield-is comprehensively discussed for MRI application in both transmitting and receiving regimes. Understanding a weakness of the previously reported HIC in transmitting regime, we suggest another HIC which is advantageous in both transmitting and receiving regimes compared to a conventional loop antenna. In contrast with the claim of previous works that the reported HICs are advantageous in transmission regime, we show only this HIC is a practical transceiver HIC. Using the perturbation approach and adding gaps to both shield and inner wire of the cable, we tune the resonance frequency to be suitable for ultra-high field (UHF) magnetic resonance imaging (MRI). These gaps reduce the quality factor of the enhanced HIC which makes its resonant frequency more stable with respect to different loadings. Our theoretical model and applicability of our HIC for MRI applications are verified by simulations. Using the theoretical model, we have designed and fabricated an array of three HICs operating at 298 MHz. The operation of the array has been experimentally studied in the presence of different phantoms used in ultrahigh field MRI and the results compared with those obtained for a conventional array.

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Section: Introductionmentioning

confidence: 99%

Analysis of High Impedance Coils Both in Transmission and Reception Regimes

et al. 2020

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“…Each method can then be combined with impedance mismatching with the preamplifier for an additional ~20–30 dB decoupling . More recently proposed decoupling paradigms include using an uneven distribution of electrical impedances around the length of the loop and high impedance coils . The decoupling technique described in Yan et al is based on the fine tuning of each coil's capacitance distribution to balance magnetic and electric coupling such that they cancel each other.…”

Section: Introductionmentioning

confidence: 99%

“…More recently proposed decoupling paradigms include using an uneven distribution of electrical impedances around the length of the loop and high impedance coils . The decoupling technique described in Yan et al is based on the fine tuning of each coil's capacitance distribution to balance magnetic and electric coupling such that they cancel each other. This technique requires a number of lumped elements whose value must be precisely calculated.…”

Section: Introductionmentioning

confidence: 99%

Shielded‐coaxial‐cable coils as receive and transceive array elements for 7T human MRI

Ruytenberg

Webb

Živković

2019

Magnetic Resonance in Med

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Purpose: To investigate the use of shielded-coaxial-cable (SCC) coils as elements for multi-channel receive-only and transceive arrays for 7T human MRI and to compare their performance with equivalently sized conventional loop coils. Methods: The SCC coil element consists of a coaxial loop with interrupted central conductor at the feed-point side and an interrupted shield at the opposite point. Interelement decoupling, transmit efficiency, and sample heating were compared with results from conventional capacitively segmented loop coils. Three multichannel arrays (a 4-channel receive-only array and 8-and 5-channel transceive arrays) were constructed. Their inter-element decoupling was characterized via measured noise correlation matrices and additionally under different flexing conditions of the coils.Thermal measurements were performed and in vivo images were acquired. Results: The measured and simulated B + 1 maps of both SCC and conventional loops were very similar. For all the arrays constructed, the inter-element decoupling was much greater for the SCC elements than the conventional ones. Even under high degrees of flexion, the coupling coefficients were lower than −10 dB, with a much smaller frequency shift than for the conventional coils. Conclusion: Arrays constructed from SCC elements are mechanically flexible and much less sensitive to changes of the coil shape from circular to elongated than arrays constructed from conventional loop coils, which makes them suitable for construction of size adjustable arrays. K E Y W O R D S7T arrays, coaxial coils, transceive coils

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“…The coil elements can potentially remain fixed from 1 application to another, while the array design can focus mainly on the design, construction, and selection of the combinational circuits that vary with the imaging protocol and ROI. To implement the proposed method into an ultra‐high field MRI scanner in practice, emerging coil decoupling methods, such as Yan et al, could be used to construct these pTx candidate array elements. Then, the magnitude and phase modulations of the combination circuitry could be fine‐tuned by collecting

B_{1}^{+}

maps of all the candidate coils in the array from a population of patients, calculated by the proposed algorithm, and they could be held fixed for all future subjects.…”

Section: Discussionmentioning

confidence: 99%

Designing parallel transmit head coil arrays based on radiofrequency pulse performance

Cao

Yan

Gore

et al. 2019

Magnetic Resonance in Med

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Purpose A new approach to design parallel transmit (pTx) head arrays is proposed that integrates transmit radiofrequency pulse designs with electromagnetic modeling of array coil elements. Theory and Methods An approach to design pTx head arrays is proposed that finds optimal groupings of a large number of coils into a small number of channels. An algorithm is proposed to extend array‐compressed parallel transmit pulse design by adding the ability to optimally select and prune coil elements, in addition to optimizing compression weights. The performance of the method is demonstrated in simulations of dynamic multislice shimming of the human brain in axial, coronal, and sagittal directions, and of reduced field‐of‐view excitation targeting the human occipital lobe, with simulated electromagnetic field maps from a group of 5 human head models at 7T. Results For both dynamic multislice shimming and reduced field‐of‐view excitation, the method successfully designed pTx arrays that simultaneously achieved in general 15% lower mean excitation errors with 20% lower SDs, along with 20% lower mean global averaged specific absorption rate and 50% lower SD than previously reported pTx head array designs. Conclusion With the proposed optimal coil element selection algorithm, the array‐compressed parallel transmit pulse design can be extended to design pTx transmit head arrays with joint consideration of the fields within the sample and the radiofrequency pulse. The pTx arrays from such an approach achieved higher transmit excitation accuracy, lower radiofrequency heating in subjects, and more robust performance across subjects compared with previously reported pTx head arrays with the same number of channels.

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Self-decoupled radiofrequency coils for magnetic resonance imaging

Cited by 69 publications

References 45 publications

Analysis of High Impedance Coils Both in Transmission and Reception Regimes

Analysis of High Impedance Coils Both in Transmission and Reception Regimes

Shielded‐coaxial‐cable coils as receive and transceive array elements for 7T human MRI

Designing parallel transmit head coil arrays based on radiofrequency pulse performance

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