Homocarnosine Spectral Editing in the Human Brain: Repeatable Brain pH Measurements at 3T with 1H-MRS

Motivation: pH variations in brain indicate disease and pathology. 1H-MRS is a sensitive technique to measure pH if homocarnosine can be easily isolated. Goal(s): Detect homocarnosine in the human brain and measure repeatability in estimating pH. Approach: Use optimal TE to isolate homocarnosine and measure its chemical shift. Henderson-Hasselbalch equation converts ppm to pH. Repeatability determined by intra- and inter-day coefficient of variation. Results: NAA and baseline signals are nulled using an optimal TE with water suppression. pH values ranged 6.96-7.04 with intra- and inter-day CV% ranging 0-0.004%. The mean and standard deviation of the intra-day ppm difference was 0.01±0.01ppm. Impact: We employ a long TE method that leverages the signal differences between homocarnosine and downfield NAA based on their T2 decay and NAA's J-evolution which enables us to repeatably measure homocarnosine and approximate pH.