Biexponential transverse relaxation (T2) of the proton MRS creatine resonance in human brain

Differences in proton MRS T2 values for phosphocreatine (PCr) and creatine (Cr) methyl groups (3.0 ppm) were investigated in studies of phantoms and human brain. Results from phantom studies revealed that T2 of PCr in solution is significantly shorter than T2 of Cr. Curve-fitting results indicated that the amplitude-TE curves of the total Cr resonance at 3.0 ppm in human brain (N = 26) fit a biexponential decay model significantly better than a monoexponential decay model (P < 0.006), yielding mean T2 values of 117 ± 21 ms and 309 ± 21 ms. Using a localized, long-TE (272 ms) point-resolved spectroscopy (PRESS) proton MRS during 2 min of photic stimulation (PS), an increase of 12.1% ± 3.5% in the mean intensity of the total Cr resonance in primary visual cortex (VI) was observed at the end of stimulation (P < 0.021). This increase is consistent with the conversion of 26% of PCr in VI to Cr, which is concordant with 31P MRS findings reported by other investigators. These results suggest a significantly shorter T2 for PCr than for Cr in vivo. This difference possibly could be exploited to quantify regional activation in functional spectroscopy studies, and could also lead to inaccuracies in some circumstances when the Cr resonance is used as an internal standard for 1H MRS studies in vivo. Magn Reson Med 47:232–238, 2002. © 2002 Wiley-Liss, Inc.