Research Article

Posterior Cingulate Lactate as a Metabolic Biomarker in Amnestic Mild Cognitive Impairment

Figure 1

1H J-resolved MRS lac imaging and analyses. (a) 3D-plot of averaged, phased proton spectra (filtered for viewing from 2 to 0.8 ppm) for 6 selected echo times (A: 72 ms, B: 92 ms, C: 112 ms, D: 232 ms, E: 252 ms, and F: 272 ms) reveals the inversion of the lac doublet located at 1.3 ppm. The full 1H spectrum at echo time of 32 ms (inset) was used to fit the classic 1H short echo NAA metabolite for absolute quantification using LCmodel. (b) Fourier transformation of the standard acquisition dimension (i.e., chemical shift) converts each FID to a frequency spectrum (F1). The NAA signal for each echo time for each individual was used for quality control purposes and for phase stabilization. No tilt correction was applied in order to inspect possible corruption by T2 noise. (c) A second Fourier transform was applied to the data along the incremented echo time (spectral dimension or F2), converting the oscillating phases of each of the coupled metabolite peaks to their respective frequency components. This contour plot of the 2D spectra, along with projections on the F1 and F2 axes over the chemical shift frequency range was used to localize, isolate, and quantify lactate at the chemical shift frequency of 1.33 ppm at J-resolved frequency of 7.5 Hz.