An 8‐element Tx/Rx array utilizing MEMS detuning combined with 6 Rx loops for ¹⁹F and ¹H lung imaging at 1.5T

Abstract

To firstly improve the attainable image signal-to-noise ratio (SNR) of 19 F and 1 H C3F8 lung imaging at 1.5T using an 8-element transmit/receive (Tx/Rx) flexible vest array combined with a 6-element Rx-only array, and secondly, to evaluate MEMS for switching the array elements between the two resonant frequencies.Methods:The Tx efficiency and homogeneity of the 8-element array was measured and simulated for 1 H imaging in a cylindrical phantom and then evaluated for in-vivo 19 F/ 1 H imaging. The added improvement provided by the 6-element Rx-only array was quantified through simulation and measurement and was compared to the ultimate SNR (uSNR). It was verified through the measurement of isolation, that MEMS switches provided broadband isolation of Tx/Rx circuitry such that the 19 F tuned Tx/Rx array could be effectively used for both 19 F and 1 H nuclei.Results: For 1 H imaging, the measured Tx efficiency/homogeneity (mean±percent standard deviation; 6.79 /√ ± 26%) was comparable to that simulated (7.57 /√ ± 20%).The 6 additional Rx-only loops increased the mean Rx sensitivity when compared to the 8element array, by a factor of 1.41x and 1.45x in simulation and measurement, respectively. In regions central to the thorax the simulated SNR of the 14-element array achieves >=70% of the uSNR when including noise from the matching circuits and preamplifiers. A measured MEMS switching speed of 12 µs and added minimum 22 dB of isolation between Tx and Rx was sufficient for Tx/Rx switching in this application. Conclusion:The described single tuned array driven at 19 F and 1 H, utilizing MEMS technology, provides excellent results for 19 F and 1 H dual-nuclear lung ventilation imaging.

Reproducibility of 19F‐MR ventilation imaging in healthy volunteers

“…The use of advanced MR coil hardware (eg, array coils) 41 may help to improve the overall SNR of 19 F‐MR images, as well as address the spread of SNR values observed between participants. This may, in part, stem from differences in coil loading associated with varying body habitus, in addition to differences in breathing efficacy relating to the gas wash‐in protocol.…”

A Review of Non-1H RF Receive Arrays in Magnetic Resonance Imaging and Spectroscopy

“…Though technically challenging, this method is especially advantageous because it ensures array operation with equal field-of-view at both frequencies. If truly simultaneous operation at both frequencies is not necessary, PIN diodes [67] – [70] , varactor diodes [71] , [72] , or MEMS switches [73] , [74] may instead be used to add or remove tuning elements into the element coil circuitry to achieve switch-tunable designs.…”

MR properties of 19F C3F8 gas in the lungs of healthy volunteers: and apparent diffusion coefficient at 1.5T and at 3T

“…Hyperpolarization (~30%-40%) of 86% enriched 129 Xe gas was performed in house using the spin-exchange optical pumping method 48 Philips, Andover, MA) using an elliptical transmit/receive quadrature birdcage coil (RAPID Biomedical, Rimpar, Germany). Experiments at 1.5T (GE HDx; GE Medical Systems, Milwaukee, WI) with 19 F were performed with an in-house constructed transceiver array, 49,50 which improves the average SNR by a factor of approximately 5 throughout the lung region when compared with a single transceiver vest coil. 129 Xe imaging at 1.5T was performed with a flexible transceiver vest coil (Clinical MR Solutions [CMRS], Brookfield, WI).…”