Active Decoupling of Transmit and Receive Coils for Full-Duplex MRI

TL;DR

This paper introduces two innovative controllable decoupling designs for full-duplex MRI, enabling effective isolation between transmit and receive coils during concurrent excitation and acquisition, thus improving detection of signals from tissues with very short T2.

Contribution

It presents novel semi-automatic and fully-automatic decoupling methods adapted from communication systems for MRI, achieving over 75 dB and 100 dB decoupling respectively.

Findings

Semi-automatic design achieves >75 dB decoupling.

Fully-automatic design achieves >100 dB decoupling.

Decoupling enables detection of signals from tissues with very short T2.

Abstract

Objective: Concurrent excitation and acquisition in MRI is a method to acquire MRI signal from tissues with very short transverse relaxation time. Since transmit power is many orders of magnitude larger than receive signal, a weak coupling dominates the MR signal during CEA. Thus, appropriate decoupling between transmit and receive coils is required. In this study, two controllable decoupling designs are investigated for achieving isolation between coils. Methods: A modified version of isolation concept used in the full-duplex radios in communication systems is applied to acquire MRI signal using CEA. In our new method, a small copy of RF transmit signal is attenuated and delayed to generate the same coupling signal which is available in the receiver coil. Then it is subtracted from the receive signal to detect the MRI signal. The proposed decoupling method is developed and implemented in two designs: Semi-Automatic and Fully-Automatic Controllable Decoupling Designs. Results: Using Semi-Automatic Controllable Decoupling Design, decoupling of more than 75 dB is achieved. Fully-Automatic Controllable Decoupling Design provides more than 100 dB decoupling between coils which is good enough for detecting MRI signals during excitation from tissues with very short transverse relaxation time. Conclusion: This study shows feasibility of applying full duplex electronics to decouple transmit and receive coils for CEA in a clinical MRI system. Significance: These designs can automatically tune the cancellation circuit and it is a potential tool for recovering signal from tissues with very short T2 in clinical MR systems with a minor hardware modification.