³¹P MRSI Coil Combination Using ²³Na Sensitivity Information

To optimally combine receive channels for ³¹P MRSI when the SNR is relatively low using sensitivity maps obtained from ²³Na signals.

This study utilized a dedicated X-nuclei 15-channel head coil array capable of imaging both ²³Na and ³¹P. After acquiring the relatively low-SNR multi-channel ³¹P MRSI signals, also the high-SNR ²³Na sensitivity information was acquired. The low-SNR ³¹P MRSI signals were combined using the high-SNR ²³Na sensitivity information, instead of the traditional self-weighting approach where ³¹P sensitivity is derived from the low-SNR ³¹P FID signals. The proposed method was evaluated by electromagnetic simulations, numerical Monte Carlo studies, and in vivo ³¹P MRSI on two healthy volunteers undergoing three independent acquisitions in total.

The electromagnetic simulations indicate a negligible SNR loss of maximum 5% by using ²³Na sensitivities for ³¹P coil combination. The Monte Carlo synthetic coil combination shows that the higher SNR of the ²³Na sensitivity information benefits the SNR of the combined ³¹P spectra. In addition, the self-weighted method is prone to introducing combination bias (SNR overestimation), while the ²³Na-based method does not. The in vivo MR experiments demonstrate an increase in SNR when using the ²³Na-based combination, as verified across three independently acquired datasets.

³¹P MRSI multi-channel signal combination using ²³Na sensitivities acquired with the same receiver array provides better performance when compared to self-weighting.