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Comparison of MEMS switches and PIN diodes for switched dual tuned RF coils.

ABSTRACT: PURPOSE:To evaluate the performance of micro-electromechanical systems (MEMS) switches against PIN diodes for switching a dual-tuned RF coil between 19 F and 1 H resonant frequencies for multi-nuclear lung imaging. METHODS:A four-element fixed-phase and amplitude transmit-receive RF coil was constructed to provide homogeneous excitation across the lungs, and to serve as a test system for various switching methods. The MR imaging and RF performance of the coil when switched between the 19 F and 1 H frequencies using MEMS switches, PIN diodes and hardwired configurations were compared. RESULTS:The performance of the coil with MEMS or PIN diode switching was comparable in terms of RF measurements, transmit efficiency and image SNR on both 19 F and 1 H nuclei. When the coil was not switched to the resonance frequency of the respective nucleus being imaged, reductions in the transmit efficiency were observed of 32% at the 19 F frequency and 12% at the 1 H frequency. The coil provides transmit field homogeneity of ±12.9% at the 1 H frequency and ±14.4% at the 19 F frequency in phantoms representing the thorax with the air space of the lungs filled with perfluoropropane gas. CONCLUSION:MEMS and PIN diodes were found to provide comparable performance in on-state configuration, while MEMS were more robust in off-state high-powered operation (>1 kW), providing higher isolation and requiring a lower DC switching voltage than is needed for reverse biasing of PIN diodes. In addition, clear benefits of switching between the 19 F and 1 H resonances were demonstrated, despite the proximity of their Larmor frequencies.

SUBMITTER: Maunder A

PROVIDER: S-EPMC6120476 | biostudies-literature | 2018 Oct

REPOSITORIES: biostudies-literature

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Comparison of MEMS switches and PIN diodes for switched dual tuned RF coils.

Maunder Adam A Rao Madhwesha M Robb Fraser F Wild Jim M JM

Magnetic resonance in medicine 20180309 4

<h4>Purpose</h4>To evaluate the performance of micro-electromechanical systems (MEMS) switches against PIN diodes for switching a dual-tuned RF coil between <sup>19</sup> F and <sup>1</sup> H resonant frequencies for multi-nuclear lung imaging.<h4>Methods</h4>A four-element fixed-phase and amplitude transmit-receive RF coil was constructed to provide homogeneous excitation across the lungs, and to serve as a test system for various switching methods. The MR imaging and RF performance of the coil ...[more]

PMID: 29524235

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Project description:Objective.A novel angle-tuned ring coil is proposed for improving the depth-spread performance of transcranial magnetic stimulation (TMS) coils and serve as the building blocks for high-performance composite coils and multisite TMS systems.Approach.Improving depth-spread performance by reducing field divergence through creating a more elliptical emitted field distribution from the coil. To accomplish that, instead of enriching the Fourier components along the planarized (x-y) directions, which requires different arrays to occupy large brain surface areas, we worked along the radial (z) direction by using tilted coil angles and stacking coil numbers to reduce the divergence of the emitted near field without occupying large head surface areas. The emitted electric field distributions were theoretically simulated in spherical and real human head models to analyze the depth-spread performance of proposed coils and compare with existing figure-8 coils. The results were then experimentally validated with field probes andin-vivoanimal tests.Main results.The proposed 'angle-tuning' concept improves the depth-spread performance of individual coils with a significantly smaller footprint than existing and proposed coils. For composite structures, using the proposed coils as basic building blocks simplifies the design and manufacturing process and helps accomplish a leading depth-spread performance. In addition, the footprint of the proposed system is intrinsically small, making them suitable for multisite stimulations of inter and intra-hemispheric brain regions with an improved spread and less electric field divergence.Significance.Few brain functions are operated by isolated single brain regions but rather by coordinated networks involving multiple brain regions. Simultaneous or sequential multisite stimulations may provide tools for mechanistic studies of brain functions and the treatment of neuropsychiatric disorders. The proposed AT coil goes beyond the traditional depth-spread tradeoff rule of TMS coils, which provides the possibility of building new composite structures and new multisite TMS tools.

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Comparison of MEMS switches and PIN diodes for switched dual tuned RF coils.

Publications

Comparison of MEMS switches and PIN diodes for switched dual tuned RF coils.

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