Improving spectral quality in fetal brain magnetic resonance spectroscopy using constructive averaging

Abstract

Purpose: A common source of loss in signal-to-noise ratio (SNR) in fetal brain magnetic resonance spectroscopy (MRS) is from fetal movement and temporal magnetic field drift. We investigated the feasibility of using constructive averaging strategies for improving the spectral quality and recovering the SNR loss from these effects.

Materials and methods: Eight fetuses, between 20 3/7 and 38 2/7 weeks' gestation, were scanned with MRS at 1.5 T. Single-voxel point-resolved spectroscopy of the fetal brain with TE = 144 ms (in one case additional TE = 288 ms) was performed in a dynamic mode, and individual spectra of 128 acquisitions were saved. With constructive averaging strategy individual acquisitions were corrected for phase variations and frequency drift before averaging. Constructively averaged spectra were compared to those using conventional averaging to evaluate differences in spectral quality and SNR.

Results: The definition of key metabolite peaks was qualitatively improved using constructive averaging, including the doublet structure of lactate in one case. Constructive averaging was associated with SNR increases, ranging from 11% to 40%, and the SNR further improved in one case when outliers from severe motion were rejected before averaging.

Conclusion: Our results demonstrate the feasibility of using constructive averaging for improving SNR in fetal MRS, which is likely to improve the characterization of fetal brain metabolites.