Double-quantum surface-coil NMR studies of sodium and potassium in the rat brain.

Double-quantum filtered and conventional single-pulse sodium and potassium NMR spectra were obtained from in situ rat brain at 7.0 T. using a surface coil. In contrast to the ca. 14% decrease observed in single-pulse sodium NMR spectra upon death, increases as large as ca. 800% were observed in double-quantum filtered sodium spectra. Conversely, a ca. 26% increase was observed in single-pulse potassium spectra upon death, while double-quantum filtered potassium spectra decreased below the noise level, for the shortest preparation time used. The decay rate of double-quantum sodium coherence in the in situ rat brain after death was dependent upon the double-quantum preparation time: this behavior results from the nonuniformity of the brain, and may be related to physiological compartmentalization. The potential application to sodium NMR imaging of cerebral functionality is briefly discussed.