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

Multiple-quantum (MQ) -filtered 23Na NMR has been proposed as a means to partially discriminate between intracellular and extracellular sodium. However, low signal-to-noise ratio (SNR) has been a major obstacle to MQ-filtered 23Na imaging becoming an important technique for biological and clinical applications. We compared the various MQ-filtered 23Na imaging pulse sequences to select the optimum sequence that provides the best SNR. The results of phantom experiments show that the gradient-echo MQ-filtered 23Na imaging sequence produces the best SNR. We also report, for the first time, three-dimensional single-quantum (SQ) and triple-quantum (TQ) -filtered 23Na images of the live dog brain and demonstrate the sensitivity of these images to ischemia produced by euthanizing the animal. The SQ images showed a 10% to 15% decrease in signal intensity from the brain post-mortem, whereas the 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 23Na images of in situ dog brain encourages us to apply this technique to humans.