Measuring T ₂ in vivo with J-difference editing: Application to GABA at 3 tesla

Purpose: To develop an experimental approach for determining in vivo transverse relaxation rates (T ₂) of metabolites that are detected by spectral editing without using simulations, and to demonstrate this approach to measure the T ₂ of γ-aminobutyric acid (GABA). Materials and Methods: The proposed method first determines the TE-dependence of the edited signals using measurements in a pure phantom solution (10 mM γ-aminobutyric acid; GABA); the phantom T ₂ is also determined. Once the editing echo time (TE) -modulation pattern is known, it can then be used to determine T ₂ in vivo. The method was applied to measure GABA T ₂ in the occipital lobe of five healthy adult subjects at 3T, using a J-difference editing method. Unwanted macromolecular contributions to the GABA signal were also measured. Results: The in vivo T ₂ of edited GABA signal was 88 ± 12 ms; this preliminary result is somewhat shorter than other metabolite T ₂ values in the literature at this field strength. Conclusion: Spectral editing methods are now widely used to detect low concentration metabolites, such as GABA, but to date no edited acquisition methods have been proposed for the measurement of transverse relaxation times (T ₂). The method described has been successfully applied to measuring the T ₂ of GABA.