A fast MOSFET rf switch for low-field NMR and MRI

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Radiofrequency Engineering
• Semiconductor Devices

Background:

• Transmit Array Spatial Encoding (TRASE) MRI requires rapid switching between RF pulses from distinct coils.
• Conventional PIN diode switches are too slow for low- and ultra-low-field MRI, causing significant delays.
• Existing methods struggle with efficient RF pulse switching and energy management in fast MRI sequences.

Purpose of the Study:

• To develop and characterize a MOSFET-based RF switch for TRASE MRI.
• To overcome the speed limitations of existing switching technologies in low-field MRI.
• To explore energy storage capabilities for enhanced MRI performance.

Main Methods:

• Designed and tested a MOSFET-based RF switch capable of high-frequency operation (up to hundreds of kHz).
• Evaluated switching speed, isolation ratio, and pulse delay.
• Investigated the use of current switching at null current and maximum voltage for series-tuned RF coils.
• Demonstrated TRASE MRI with MOSFET switches and compared performance to reed relays.

Main Results:

• The MOSFET switch achieves sub-microsecond switching with negligible delay and high isolation.
• Efficient RF energy storage in tuning capacitors for extended periods (seconds) was demonstrated.
• A threefold acceleration in TRASE phase-encoding was achieved using MOSFET switches compared to reed relays.

Conclusions:

• MOSFET-based RF switches offer a viable solution for high-speed coil switching in low-field TRASE MRI.
• The developed technology significantly reduces pulse delays and enables faster imaging.
• This approach holds potential for applications beyond TRASE MRI, including fast repeated spin-echo experiments.