Measuring transverse relaxation rates of the major brain metabolites from single-voxel PRESS acquisitions at a single TE.

Purpose: To compare transverse relaxation rates of brain metabolites estimated from single-TE PRESS acquisitions with more conventionally derived rates estimated from multiple-TE PRESS acquisitions.

Methods: Single-voxel (8 mL) PRESS data within white matter from 6 subjects were acquired at five different TEs. Transverse relaxation rates R of N-acetylaspartate, creatine, and choline were estimated from a single TE using full versus right-side-only sampling of the echo. These R values were compared with R values obtained from the multiple-TE PRESS acquisitions.

Results: Following baseline subtraction and RMS weighting, interindividual mean R values from TE = 288 ms magnitude spectra for choline, creatine, and N-acetylaspartate were highly correlated with respective R values (r = 0.99). Paired individual measurements at this TE showed less correlation (r = 0.48), primarily due to the N-acetylaspartate resonance. Using TE = 360 ms data for N-acetylaspartate and 288 ms for choline and creatine resulted in an improved correlation coefficient (r = 0.80). The average absolute intra-individual differences in the estimated R s between single-TE and Hahn method was 9.6 ± 7.7%.

Conclusion: For the major brain metabolite singlets, R values showed correlations with more fragile measurements of R from a single TE that are worthy of interest. Because the left side of long-TE spin echoes is available "for free" from an acquisition perspective, and although the single-TE method for estimating R values is associated with lower precision, the reduction in scan time may be clinically helpful.