Spectroscopic assessment of alterations in macromolecule and small-molecule metabolites in human brain after stroke

Background and Purpose-We sought to measure the temporal evolution and spat ial distribution of lesion macromolecules and small molecules (lactate, N-a cetyl compounds. creatine, and choline) in stroke patients by using short e cho time in vivo proton MR spectroscopy. Methods-Single-voxel spectra with TE = 22 ms were obtained with and without inversion recovery suppression of small-molecule resonances from 30 examin ations of 24 patients 3 to 214 days after stroke. Subtraction of the suppre ssed from the unsuppressed spectra yielded metabolite spectra without overl ap from macromolecules. Two-dimensional spectroscopic images were acquired with macromolecule and small-molecule suppression from 5 additional patient s. Results-Macromolecule signals were elevated in lesions relative to normal b rain and tended to increase in the subacute period, even as lactate peaks d eclined. Regions of increased lactate, increased macromolecule signal at 1. 3 ppm, and decreased N-acetyl compounds were closely correlated in the 2D s pectroscopic images. Conclusions-Short echo time spectra can be acquired in vivo in a manner tha t improves signal-to-noise ratio over long echo experiments and resolves ov erlapping macromolecule and small-molecule signals. The prominent macromole cule signals seen in the subacute period in association with persistently e levated lactate may represent mobile lipids in macrophages or other cells.