Characterize the Membrane Phospholipids 31P MRS Signal in Human Brain at 7T

Motivation: Human brain 31P-MR spectra often show a broad membrane phospholipid (MPL) signal, which has an intensity far exceeding all other sharp signals combined and a linewidth of ~ 15 ppm. Despite its spectral dominance and distortive effect on the sharp 31P peaks, this MPL signal has received little NMR characterization. Goal(s): Measure MPL T2 relaxation time, estimate its concentration, and demonstrate MPL chemical exchange effect. Approach: Chemical exchange was measured by inversion-recovery method, and T2 by varying the delayed time of FID-sampling. Results: MPL has a short T2 (0.1 ms), and high concentration (1.2 M), and present with internal chemical exchange within its structure. Impact: MPL signals can be selectively detected using 31P MRS in the human brain. High concentration of MPL in the order of 1M may provide a valuable surrogate point for studying demyelination process in neurodegenerative diseases such as multiple sclerosis (MS).