Low visibility of lactate in excised rat muscle using double quantum proton spectroscopy

Lactate NMR visibility was investigated in excised rat muscle at 3 T by comparing the concentration determined in situ by double quantum (DQ) proton spectroscopy (150 ms effective echo time) to the concentration measured in vitro from perchloric acid extracts of the same muscle samples. After 1-2 h of ischemia, lactate NMR visibility was 32 +/- 3% (+/- SE, n = 9), and was only 21 +/- 1% (n = 6) after 10-12 h. Muscle lactate T2 was 140 +/- 11 ms and 184 +/- 6 ms, respectively. All potential mechanisms of DQ lactate signal attenuation (B0 and B1 inhomogeneity, DQ transverse relaxation, diffusion) were examined, and accounted for when necessary. A significant increase in lactate NMR visibility was demonstrated using a shorter effective echo time (79 ms) DQ editing sequence. These results are interpreted as reflecting muscle lactate compartmentation between a long T2 pool predominantly detected by DQ spectroscopy, and a short T2 pool virtually invisible with longer echo time NMR techniques.