In vivo T sub(2) relaxation time measurement with echo-time averaging

• Published in: NMR in biomedicine Vol. 27; no. 8; pp. 863 - 869
• Main Authors: Prescot, Andrew P, Shi, Xianfeng, Choi, Changho, Renshaw, Perry F
• Format: Journal Article
• Language: English
• Published: 01.08.2014
• ISSN: 0952-3480; 1099-1492
• DOI: 10.1002/nbm.3115

The accuracy of metabolite concentrations measured using in vivo proton ( super(1)H) MRS is enhanced following correction for spin-spin (T sub(2)) relaxation effects. In addition, metabolite proton T sub(2) relaxation times provide unique information regarding cellular environment and molecular mobility. Echo-time (TE) averaging super(1)H 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 T sub(2) relaxation information, the aim of the present proof-of-concept study was to develop a novel data processing scheme to estimate metabolite T sub(2) relaxation times from TE-averaged super(1)H MRS data. Spectral simulations are used to validate the proposed TE-averaging methods for estimating methyl proton T sub(2) 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 T sub(2) estimates closer to reported values when maximum TE approximately T sub(2), and the potential for T sub(2) calculation of metabolite resonances otherwise inseparable in standard super(1)H MRS spectra recorded in vivo. Copyright copyright 2014 John Wiley & Sons, Ltd. A novel method based on the echo-time (TE) averaged super(1)H MRS method is introduced for estimating cerebral metabolite proton spin-spin (T sub(2)) relaxation times. The technique works by TE averaging across two distinct TE subarrays and using relative signal attenuation effects to calculate T sub(2). The method was initially validated through simulation procedures and compared directly with results obtained using standard T sub(2) curve fitting. Subsequently, the technique was used to estimate in vivo T sub(2) relaxation times for choline-containing compounds, N-acetyl aspartate, and total creatine in 10 healthy adult subjects. The resulting in vivo T sub(2) values agreed well with precedent literature values and showed excellent within-subject reproducibility. Several key advantages of the new approach are identified and discussed.