A high-dynamic-range digital RF-over-fiber link for MRI receive coils using delta-sigma modulation

Area of Science:

• Medical Imaging Technology
• Electrical Engineering
• Biomedical Engineering

Background:

• Coaxial cables in MRI scanners are prone to electromagnetic coupling, causing heating and safety issues as radio-frequency (RF) channel counts increase.
• Existing fiber-optic solutions struggle with the high dynamic range required for typical MRI signals (>80 dB).

Purpose of the Study:

• To develop a digital fiber-optic transmission system using delta-sigma modulation (DSM) to overcome limitations of current MRI signal transmission.
• To enable safe and efficient transmission of high-bandwidth MRI signals, improving overall system performance and safety.

Main Methods:

• A delta-sigma modulation (DSM)-based optical link was prototyped using off-the-shelf components.
• Bench testing was performed at various oversampling rates (OSRs) to evaluate performance.
• A custom fourth-order continuous-time DSM was designed in 180 nm CMOS technology for full-bandwidth MRI signal transmission.

Main Results:

• An end-to-end dynamic range (DR) of 81 dB was achieved over a 200 kHz bandwidth (OSR=50) with the prototype.
• The custom DSM chip is designed to handle full-bandwidth MRI signals up to 1 MHz with adequate dynamic range.
• Initial electrical test results from the custom CMOS chip are presented.

Conclusions:

• The developed digital fiber-optic DSM system effectively addresses electromagnetic coupling and dynamic range challenges in MRI RF signal transmission.
• The custom DSM chip shows promise for enabling high-fidelity, full-bandwidth MRI signal transmission, enhancing scanner safety and capabilities.