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

Abstract

PurposeTo evaluate the performance of micro‐electromechanical systems (MEMS) switches against PIN diodes for switching a dual‐tuned RF coil between 19F and 1H resonant frequencies for multi‐nuclear lung imaging.MethodsA 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 19F and 1H frequencies using MEMS switches, PIN diodes and hardwired configurations were compared.ResultsThe performance of the coil with MEMS or PIN diode switching was comparable in terms of RF measurements, transmit efficiency and image SNR on both 19F and 1H 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 19F frequency and 12% at the 1H frequency. The coil provides transmit field homogeneity of ±12.9% at the 1H frequency and ±14.4% at the 19F frequency in phantoms representing the thorax with the air space of the lungs filled with perfluoropropane gas.ConclusionMEMS 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 19F and 1H resonances were demonstrated, despite the proximity of their Larmor frequencies.

Optimization of steady‐state free precession MRI for lung ventilation imaging with 19F C3F8 at 1.5T and 3T

“…Rectangular (24 cm × 16 cm) transceive single loop coils were constructed from 11 mm width copper strip, tuned and matched at the 1.5T (GE Signa HDx) (60 MHz) and 3T (Philips Ingenia) (120 MHz) frequencies and centered with the cylinders during imaging. Before the phantom studies at 1.5T and 3T, FA maps were generated by varying the input power in SPGR imaging with TR 100 ms» T 1 and fitting the received signal according to Equation , as in Maunder et al The prescribed FA recorded in Table for the imaging performed with the glass phantoms was based on the fitted FA at the center of the phantom. Furthermore, to ensure that SNR and relaxation parameters were not inaccurately calculated due to B 1 inhomogeneity, voxelwise parameter mapping was calculated using the voxelwise fitted FA map rather than a prescribed mean value.…”

Design of a RF Switch Used in Redundant Atomic Clock Configurations

“…Different RF switches have different mechanical and electrical structures, so their switching speed, isolation, insertion loss, return loss and other technical metrics are also different [20]. At present, common RF switches are mainly divided into two categories: electromechanical switches and solid-state switches [21,22]. Depending on the different components, solid-state switches can be roughly divided into FET switches and PIN switches.…”

Optimization of high-channel count, switch matrices for multinuclear, high-field MRI

“…Crossbar switch matrix implementations can either be achieved with the use of integrated circuits configured as single-pole double-throw (SPDT) switches, e.g. based on GaAs, GaN [ 23 ], or MEMS [ 24 ] switches, or by employing simpler single-pole single-throw (SPST) configurations, e.g. by using PIN-diodes.…”