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 spatial distribution of lesion macromolecules and small molecules (lactate, N-acetyl compounds, creatine, and choline) in stroke patients by using short echo 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 examinations of 24 patients 3 to 214 days after stroke. Subtraction of the suppressed from the unsuppressed spectra yielded metabolite spectra without overlap from macromolecules. Two-dimensional spectroscopic images were acquired with macromolecule and small-molecule suppression from 5 additional patients. Results— Macromolecule signals were elevated in lesions relative to normal brain and tended to increase in the subacute period, even as lactate peaks declined. Regions of increased lactate, increased macromolecule signal at 1.3 ppm, and decreased N-acetyl compounds were closely correlated in the 2D spectroscopic images. Conclusions— Short echo time spectra can be acquired in vivo in a manner that improves signal-to-noise ratio over long echo experiments and resolves overlapping macromolecule and small-molecule signals. The prominent macromolecule signals seen in the subacute period in association with persistently elevated lactate may represent mobile lipids in macrophages or other cells.