High efficiency radiofrequency power amplifier module for parallel transmit arrays at 3 Tesla

Area of Science:

• Magnetic Resonance Imaging
• RF Engineering
• Solid-State Electronics

Background:

• Parallel transmit (pTX) arrays enhance MRI performance but require efficient, high-power radiofrequency power amplifiers (RFPAs).
• Existing RFPA solutions for pTX systems can be bulky and costly, limiting widespread adoption.
• Developing compact and efficient RFPAs is crucial for advancing MRI technology.

Purpose of the Study:

• To develop an in-bore radiofrequency power amplifier (RFPA) module for 3 Tesla (T) parallel transmit (pTX) arrays.
• The module aims for high power efficiency and density, crucial for advanced MRI applications.
• To enable more cost-effective implementation of pTX systems in MRI.

Main Methods:

• Utilized a combination of current mode class D, S, and E amplifiers.
• Employed enhancement-mode gallium nitride-on-silicon field-effect transistors.
• Implemented envelope elimination and restoration for efficient amplitude modulation.
• Conducted pulsed RF measurements for nonlinearity and efficiency over a 37 dB dynamic range.
• Assessed thermal performance with and without forced convection cooling.

Main Results:

• Achieved peak radiofrequency (RF) power output up to 130 W.
• Attained an overall module efficiency of 85%.
• Maintained maximum junction temperatures below 80°C at 100 W RF pulses (10% duty cycle) without heatsinks or forced convection.
• Demonstrated high power density and efficiency.

Conclusions:

• The developed in-bore RFPA module offers high power efficiency and density.
• Its small size and low cost facilitate more affordable pTX system implementation compared to remote linear RFPAs.
• Further research is needed to address control of RF output nonlinearities and coupling.