A Low-Cost and Compact High-Frequency Gallium Nitride Gradient Power Amplifier for Low-Field MRI

To reduce the upfront cost of small, low-field MRI systems, while expanding the capabilities of their gradient systems.

A gradient power amplifier was designed to leverage the lowering cost of Gallium Nitride (GaN) power transistors and high speed logic, to achieve high efficiency and responsiveness for driving gradient coils. The switching H-bridge design was realized as a prototype and tested to determine power output capabilities. With a digital control system, the prototype was further tested using a load which simulates a small gradient, such as those used in head and extremity low-field MRI systems. Additionally in this test, the noise spectra produced in operation are analyzed.

The amplifier combined with an example control system to drive 15 A into a $225\mu H$ , $0.3\Omega$ load simulating an effective strength over 15 mT/m and slew over 32 T/m/s, has a total build cost of under US$300 and an amplifier size under $6\times 6\times 2\text{cm}$ . High efficiency allows for this performance with no active cooling at full duty cycle, and high frequency switching produces controllable interference when imaging frequencies lay in the same range.

Using GaN transistors, a low-cost gradient amplifier can be implemented that will reduce the cost and size of low-field MRI systems, improving accessibility.