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 b y comparing the concentration determined in situ by double quantum (DQ ) proton spectroscopy (150 ms effective echo time) to the concentratio n measured in vitro from perchloric acid extracts of the same muscle s amples, 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 l actate T-2 was 140 +/- 11 ms and 184 +/- 6 ms, respectively. All poten tial mechanisms of DQ lactate signal attenuation (B-0 and B-1 inhomoge neity, DQ transverse relaxation, diffusion) were examined, and account ed for when necessary. A significant increase in lactate NMR visibilit y was demonstrated using a shorter effective echo time (79 ms) DQ edit ing sequence. These results are interpreted as reflecting muscle lacta te compartmentation between a long T-2 pool predominantly detected by DQ spectroscopy, and a short T-2 pool virtually invisible with longer echo time NMR techniques.