Optimized methods for robust calculation of chemical shifts in hyperpolarized 129Xe MR spectroscopy

Motivation: Hyperpolarized 129Xe RBC chemical shift is an increasingly important biomarker for lung disease, but the robustness of its calculation has not been investigated. Goal(s): The aim of this study is to identify a more accurate and optimal method of calculating RBC chemical shift in 129Xe MRS compared to standard practice. Approach: We investigated two approaches for the 0-ppm 129Xe gas-phase reference frequency: 1) the incidental gas signal arising during RBC excitation and 2) a dedicated gas excitation. Results: RBC shifts calculated using dedicated gas-phase references were found to be more repeatable and potentially more accurate than standard incidental references. Impact: Using dedicated 129Xe gas-phase excitation to calculate the 0-ppm reference frequency yielded more repeatable and accurate quantifications of the RBC shift than standard practice, enabling more robust characterization of lung disease via 129Xe MRS.