Design and Development of a General‐Purpose Transmit/Receive (T/R) Switch for 3T MRI, Compatible for a Linear, Quadrature and Double‐Tuned RF Coil

Abstract

This work presents the design and development of a general-purpose T/R switch for MR imaging and spectroscopy, compatible with single and double-tuned RF coils using linear, quadrature, or both modes at a low cost and with minimum development time using simple electronic circuits. This T/R switch was demonstrated with a custom double-tuned 1 H/ 31 P transmit receive surface RF coils built for 31 P MRS of a lamb's heart with surgically created congenital heart defects. Two passive trap circuits tuned to 1 H and 31 P frequencies fed from a common drive point were built to filter two different frequency T/R switches. The T/R switch was built for a 1 H linear RF coil and 31 P quadrature RF coil. This T/R switch design is easily modifiable to linear, quadrature and double-tuned RF coils of relatively wide range of frequencies, so as to enable imaging of proton and X-nuclei at 3T field. The performance of the custom T/R switch was tested with bench measurements of its isolation, insertion loss and switching time, under pulsed conditions, and on a phantom with a 3T magnet by comparing the signal-to-noise ratio with a commercial T/R switch. A high isolation, low insertion loss and fast switching time in the range of nanoseconds were obtained on the bench. Identical isolation was observed under pulsed conditions. An improvement of about 29% gain in signal-to-noise ratio was obtained with this T/R switch compared to the commercial T/R switch.

Design of a high power PIN‐diode controlled switchable RF transmit array for TRASE RF imaging

“…In the very early history of biomedical NMR, Bendall experimented with mechanical reed relays for this purpose, which had a major disadvantage in that they could not be located within the magnetic field. In 1986, Edelstein, using some of Bendall's circuit concepts demonstrated the use of actively switched PIN diodes in MRI; see also . The PIN diode is a small semiconductor two terminal component suitable for RF signal control which switched between low resistance forward bias (“On”) and high impedance reverse bias (“Off”) states.…”

“…In 1986, Edelstein, 7 using some of Bendall's circuit concepts demonstrated the use of actively switched PIN diodes in MRI; see also. 8,9 The PIN diode is a small semiconductor two terminal component suitable for RF signal control which switched between low resistance forward bias ("On") and high impedance reverse bias ("Off") states. An example of state-of-the-art use of PIN diodes to achieve very rapid switching using a feedback approach on the diode bias voltage is given by Brunner.…”

High peak and high average radiofrequency power transmit/receive switch for thermal magnetic resonance

“…The strategic placement of the λ/4 stubs routes the RF signal from the transmitter directly to the RF coil/antenna without directly passing through any lossy electronic components such as PIN diodes . This enables the use of high average powers in comparison to other Tx/Rx switches designed for MRI applications . For instance, the conventional Tx/Rx design that was used as a reference in this study uses PIN diodes in the transmission path that exhibit a series resistance of 0.35 Ω and 2 pF.…”

“…27 This enables the use of high average powers in comparison to other Tx/Rx switches designed for MRI applications. [22][23][24] For instance, the conventional Tx/Rx design that was used as a reference in this study uses PIN diodes in the transmission path that exhibit a series resistance of 0.35 X and 2 pF. The thermal resistance of these PIN diodes is 5.5 8C/W and the junction temperature is 150 8C.…”

Eight‐channel decoupled array for cervical spinal cord imaging at 3T: six‐channel posterior and two‐channel anterior array coil

“…3 a) are slightly deformed from the shape and size of the elements arranged on the planar surface (Fig. 33 When the active trap is activated by forward biasing the PIN diode D 1 (MA4P7104F, MACOM Technology Solutions Inc., CA, USA) using 100 mA DC current from the MRI scanner, the L m and C m of the trap would form a parallel LC circuit, which deactivates the element by creating an equivalent open circuit at the coil input terminals. A circuit schematic diagram for an individual element of the CSC array is shown in Fig.…”