Three-dimensional triple-quantum-filtered Na-23 imaging of the dog head invivo

Multiple-quantum (MQ) -filtered Na-23 NMR has been proposed as a means to p artially discriminate between intracellular and extracellular sodium. Howev er, low signal-to-noise ratio (SNR) has been a major obstacle to MQ-filtere d Na-23 imaging becoming an important technique for biological and clinical applications. We compared the various MQ-filtered Na-23 imaging pulse sequ ences to select the optimum sequence that provides the best SNR. The result s of phantom experiments show that the gradient-ache MQ-filtered Na-23 imag ing sequence produces the best SNR. We also report, for the first time, thr ee-dimensional single-quantum (SQ) and triple-quantum (TQ) -filtered Na-23 images of the live dog brain and demonstrate the sensitivity of these image s to ischemia produced by euthanizing the animal. The SQ images showed a 10 % to 15% decrease in signal intensity from the brain postmortem, whereas th e TQ-filtered images showed a 40% to 50% increase. These changes in signal intensities are consistent with the influx of Na+ into the cells upon death . The feasibility of obtaining TQ-filtered Na-23 images of in situ dog brai n encourages us to apply this technique to humans.