A System for Retrofitting Conventional MRI Systems for Simultaneous Multinuclear MRI/MRS

Proton magnetic resonance imaging (MRI) and spectroscopy (MRS) are widely used in clinical and research applications. Recent interest in X-nuclei studies highlights their ability to provide additional biochemical information, but the intrinsically low X-nuclear signal-to-noise ratio (SNR) significantly increases scan time. Simultaneous (rather than serial) acquisition of multiple nuclei can significantly reduce experiment time, but most conventional MR systems lack this capability without modifications. We present a cost-effective system that enables simultaneous multinuclear imaging and spectroscopy on conventional MR spectrometers. Our approach offers enhanced flexibility for multinuclear experiments, supports multinuclear array receive capability, and maintains phase stability in the radio frequency (RF) chain. The proposed system comprised multiple transmit and receive mixing channels and a four-channel flexible local oscillator (LO) source. By interfacing with the spectrometer, simultaneous transmit and receive at different frequencies were achieved. The performance of the system was evaluated through bench measurement and phantom multinuclear MRI and MRS experiments. Transmit and receive channel isolation of better than 30 dB was measured on the bench. Simultaneous excitation and reception of ²H and ²³Na gradient echo images were acquired, as well as interleaved excitation with simultaneous reception of ¹H, ²H, and ²³Na FIDs. Water-suppressed ¹H and ³¹P MRS were performed simultaneously on phantoms mimicking muscle metabolites. Results across all experiments showed no signal-to-noise ratio (SNR) loss compared to single-frequency operation. The proposed system supports multiple variations of simultaneous experiments on conventional MRI systems, demonstrating its flexibility in configuring experiments with varying numbers of nuclei (2-4), different transmit modes (simultaneous or interleaved), and supporting receive array coils of up to 16 channels, while maintaining phase stability in the RF chain without the need for retrospective correction.