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

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 ¹H/³¹P transmit receive surface RF coils built for ³¹P MRS of a lamb's heart with surgically created congenital heart defects. Two passive trap circuits tuned to ¹H and ³¹P 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 ¹H linear RF coil and ³¹P 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.