A Receive-only Frequency Translation System with Automatic Phase Correction for Simultaneous Multi-nuclear MRI/MRS.

Abstract

Objective: Receive-only frequency translation enables MRI scanners with X-nuclear capabilities to perform simultaneous/interleaved multi-nuclear experiments. Mixing only on the receive side avoids modifying the transmit path, which often has narrow-band components. However, phase incoherence is introduced at the radio frequency mixer due to differing local oscillator frequencies between transmit and receive, necessitating phase correction. This paper presents a hardware solution for automatic phase correction during scans, eliminating the need for retrospective correction and allowing flexible scan parameter adjustments.

Methods: The hardware solution detects phase changes in the system LO (local oscillator) between transmit and receive, calculates, and applies phase correction in the translator LO in real time. Programming spare TTL signals and accessing the scanner system LO are required to implement the phase correction method.

Results: Phase correction accuracy was evaluated via averaged 31P spectroscopy and 23Na imaging. On top of the noise introduced by the additional mixer, the imperfect phase correction resulted in approximately 3% SNR loss at both frequencies. The corrected 23Na signal exhibited approximately an 8-degree phase standard deviation, compared to 6 degrees in the reference signal.

Conclusion: The proposed hardware solution effectively corrects phase incoherence introduced by receive-only frequency translation. While minor imperfection exists, future upgrades are expected to improve the phase correction accuracy.

Significance: This approach eliminates the need for retrospective phase correction when using receive-only frequency translation techniques for multi-nuclear acquisition, enabling real-time data acquisition and greater flexibility in scan parameter adjustment for simultaneous/interleaved multi-nuclear experiments.