Design of Switch-Mode Amplifier to Transform Single Transmit Hardware for Multi-Nuclear MRI

This technology includes the design and implementation for 1H-nuclear magnetic resonance imaging (MRI) that allows single transmit hardware to be "transformed" for another nucleus excitation to perform multi-nuclear MR. A radiofrequency (RF) optically controlled switch-mode amplifier prototype is tuned for excitation of two nuclei. The amplifier received the nuclei carrier signals optically through a single fiber. This signal is amplified first through a broadband low current stage that provides a pair of gate-source voltage signals 180 degrees out of phase to switch ON a pair of field effect transistors (FETs) in push-pull class-D configuration (FET are turned ON only during half a cycle). In this preamplification stage gate circuitry has been dual tuned, through a dual-resonance LC network, for maximizing the gate-source voltage to fully switch ON the FETs at the selected nuclei frequencies. A similar approach is followed to permit the gate control signals to fully switch ON the FETs of the power stage in Current-Mode Class-D topology. A prototype for 1H and 31P excitation at 7T was implemented, tested on the bench and MRI scanner.