In vivo observation of anisotropic motion of brain water using ²H double quantum filtered NMR spectroscopy

The ²H DQF NMR spectra of deuterated water molecules were measured for the first time in in vivo rat brain. The observation of the DQF signal indicates that there is a water population that exhibits anisotropic motion. The characteristics of the DQF spectra premortem and postmortem are very similar (lineshape and relaxation times). In the 1st h there is a 10-15% decrease in the signal intensity of the DQF spectra followed by a gradual but a much slower decrease in the DQF signal intensity that reaches 65-70% of its initial value after only 12 h. When the brains were kept at 4°C, a 40% decrease in the DQ signal intensity was observed only after 7 days. Mechanical chopping of the brain tissues causes an immediate loss of more that 97% of the DQ signals. The slow, temperature-sensitive decay of the signal, and its sensitivity to mechanical treatment point out that these signals originate from water molecules that interact with structural components in the brain. The characteristics of the DQF spectra depend on the amount of bulk water as exemplified by increased residual quadrupolar interaction and relaxation rates obtained when dehydrating the brain tissue.