RELATIVE PHOSPHOCREATINE AND NUCLEOSIDE TRIPHOSPHATE CONCENTRATIONS IN CEREBRAL GRAY AND WHITE-MATTER MEASURED IN-VIVO BY P-31 NUCLEAR-MAGNETIC-RESONANCE

Rates of ATP metabolism generally are higher in cerebral gray matter c ompared to white matter. In order to study the physiology of this regi onal difference in vivo, the 1-dimensional chemical shift imaging tech nique (1D-CSI) was used to acquire P-31 nuclear magnetic resonance spe ctra from 2.5 mm slices of 4-week old piglet brains. Spectra from pred ominantly gray matter slices (estimated 76% gray matter, 7 mm below th e scalp) were compared to predominantly white matter slices (56% estim ated white matter, 13 mm below the scalp) as assessed by magnetic reso nance images. The 1D-CSI technique introduced no systematic changes in the ratio of signals from a single chamber phantom containing a phosp hocreatine (PCr) and ATP solution. Gray matter slices showed a PCr/NTP ratio of 0.93 +/- 0.11 (mean +/- S.D.) using a 2 s interpulse interva l, a value very close to the ratio in surface coil localized spectra. The predominantly white matter slices showed a PCr/NTP ratio of 1.32 /- 0.18 (P < 0.02 for gray versus white matter). Using the estimated p ercentages of gray and white matter in the two slices and calculated c oncentrations from fully relaxed spectra, the gray matter PCr/NTP rati o is approximately 0.77, while the ratio in white matter is approximat ely 2.18. The difference in PCr/NTP measured in vivo suggests that eit her the total NTP concentration is higher or the steady state PCr conc entration is lower in gray matter than in white matter in the piglet b rain.