In vivo T₂ relaxation time measurement with echo-time averaging

The accuracy of metabolite concentrations measured using in vivo proton (¹H) MRS is enhanced following correction for spin-spin (T₂) relaxation effects. In addition, metabolite proton T₂ relaxation times provide unique information regarding cellular environment and molecular mobility. Echo-time (TE) averaging ¹H MRS involves the collection and averaging of multiple TE steps, which greatly simplifies resulting spectra due to the attenuation of spin-coupled and macromolecule resonances. Given the simplified spectral appearance and inherent metabolite T₂ relaxation information, the aim of the present proof-of-concept study was to develop a novel data processing scheme to estimate metabolite T₂ relaxation times from TE-averaged ¹H MRS data. Spectral simulations are used to validate the proposed TE-averaging methods for estimating methyl proton T₂ relaxation times for N-acetyl aspartate, total creatine, and choline-containing compounds. The utility of the technique and its reproducibility are demonstrated using data obtained in vivo from the posterior-occipital cortex of 10 healthy control subjects. Compared with standard methods, distinct advantages of this approach include built-in macromolecule resonance attenuation, in vivo T₂ estimates closer to reported values when maximum TE≈T₂, and the potential for T₂ calculation of metabolite resonances otherwise inseparable in standard ¹H MRS spectra recorded in vivo.