Rethinking Neurochemical Distributions in White Matter and Grey Matter: Considerations for Improved Magnetic Resonance Spectroscopy Measures

Motivation: Current methods to quantify neurochemical concentrations in magnetic resonance spectroscopy (MRS) assume an equal distribution of neurochemicals between white matter (WM) and grey matter (GM), however, the implications of this assumption have not been explored. Goal(s): We aimed to improve the accuracy of MRS concentration measures by replacing assumptions with calculated values. Approach: We compared calculated concentration ratios of six neurochemicals in WM and GM with the assumed 1:1 ratio to determine the impact of assuming a 1:1 ratio on neurochemical concentrations. Results: The 1:1 ratio assumption yielded estimate errors of up to 55%. Impact: Implementation of our calculated white and grey matter neurochemical distributions will yield magnetic resonance spectroscopy concentration measures that are ~30-55% more accurate than conventional methods.