Keywords: Spectroscopy, biomarkers
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.
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