Optically controlled switch-mode current-source amplifiers for on-coil implementation in high-field parallel...

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Radiofrequency Engineering
• Biomedical Engineering

Background:

• Parallel transmission (pTX) in high-field MRI requires efficient and compact radiofrequency (RF) amplifiers.
• Integrating RF amplifiers directly with transmit coils is challenging due to space and electromagnetic interference constraints.

Purpose of the Study:

• To test the feasibility of implementing parallel transmission (pTX) for high-field MRI.
• To design and evaluate a miniaturized RF amplifier for on-coil or near-coil placement.

Main Methods:

• A current-source switch-mode amplifier using miniaturized, nonmagnetic electronics was designed.
• Optical RF signals were used for amplifier control, derived from the scanner's RF source via a custom interface.
• Performance was assessed through benchtop measurements and MRI imaging at 7T and 11.7T, evaluating interchannel coupling and phase adjustment.

Main Results:

• The amplifier delivered over 44 W RF power with minimal MRI interference.
• Accurate optical control signals were generated for carrier frequencies from 64 to 750 MHz.
• Interchannel decoupling better than 14 dB was achieved between closely spaced coil loops (1 cm), enabling artifact-free 7T and 11.7T MRI.

Conclusions:

• An optically controlled, miniaturized RF amplifier suitable for on-coil implementation at high magnetic fields was developed.
• This technology facilitates the implementation of high-density pTX arrays for advanced MRI applications.