31 P MRSI Coil Combination Using 23 Na Sensitivity Information

ABSTRACT Purpose To optimally combine receive channels for 31 P MRSI when the SNR is relatively low using sensitivity maps obtained from 23 Na signals. Methods This study utilized a dedicated X‐nuclei 15‐channel head coil array capable of imaging both 23 Na and 31 P. After acquiring the relatively low‐SNR multi‐channel 31 P MRSI signals, also the high‐SNR 23 Na sensitivity information was acquired. The low‐SNR 31 P MRSI signals were combined using the high‐SNR 23 Na sensitivity information, instead of the traditional self‐weighting approach where 31 P sensitivity is derived from the low‐SNR 31 P FID signals. The proposed method was evaluated by electromagnetic simulations, numerical Monte Carlo studies, and in vivo 31 P MRSI on two healthy volunteers undergoing three independent acquisitions in total. Results The electromagnetic simulations indicate a negligible SNR loss of maximum 5% by using 23 Na sensitivities for 31 P coil combination. The Monte Carlo synthetic coil combination shows that the higher SNR of the 23 Na sensitivity information benefits the SNR of the combined 31 P spectra. In addition, the self‐weighted method is prone to introducing combination bias (SNR overestimation), while the 23 Na‐based method does not. The in vivo MR experiments demonstrate an increase in SNR when using the 23 Na‐based combination, as verified across three independently acquired datasets. Conclusion 31 P MRSI multi‐channel signal combination using 23 Na sensitivities acquired with the same receiver array provides better performance when compared to self‐weighting.