A High-Dynamic-Range Digital RF-Over-Fiber Link for MRI Receive Coils Using Delta-Sigma Modulation

TL;DR

This paper introduces a novel digital fiber-optic transmission system using delta-sigma modulation for MRI receive coils, achieving high dynamic range and safety improvements over traditional coaxial cables.

Contribution

The work presents a new DSM-based optical link prototype and a custom CMOS DSM chip, enabling high-dynamic-range MRI signal transmission over fiber-optic cables.

Findings

Achieved 81 dB dynamic range over 200 kHz bandwidth with the prototype.

Designed a fourth-order continuous-time DSM chip for full-bandwidth MRI signals.

Demonstrated initial electrical performance of the custom DSM chip.

Abstract

The coaxial cables commonly used to connect RF coil arrays with the control console of an MRI scanner are susceptible to electromagnetic coupling. As the number of RF channel increases, such coupling could result in severe heating and pose a safety concern. Non-conductive transmission solutions based on fiber-optic cables are considered to be one of the alternatives, but are limited by the high dynamic range ($>80$~dB) of typical MRI signals. A new digital fiber-optic transmission system based on delta-sigma modulation (DSM) is developed to address this problem. A DSM-based optical link is prototyped using off-the-shelf components and bench-tested at different signal oversampling rates (OSR). An end-to-end dynamic range (DR) of 81~dB, which is sufficient for typical MRI signals, is obtained over a bandwidth of 200~kHz, which corresponds to $OSR=50$. A fully-integrated custom fourth-order continuous-time DSM (CT-DSM) is designed in 180~nm CMOS technology to enable transmission of full-bandwidth MRI signals (up to 1~MHz) with adequate DR. Initial electrical test results from this custom chip are also presented.