Quantitative tissue sodium concentration mapping of normal rat brain

A quantitative in vivo method for obtaining maps of tissue sodium concentration (TSC) by MRI is compared to the invasive, global Na-22 radionuclide dilutional technique in the normal rat brain, The NIR method uses a three-dimensional projectional acquisition scheme to minimize signal losses from transverse relaxation, Internal calibration standards are used to convert the signal intensity into TSC after correction for B-1 inhomogeneities by using the ratio of Na-23 and H-1 images obtained with identical B-1 distributions and sensitivities at the two frequencies, Over the biological range of concentrations, the TSC, measured as the ratio of MR signals of Na-23 and H-1, gives a linear response with concentration, In the normal rat brain, the mean TSC measured using the MRI method (TSC = 45 +/- 4 mM, animals = 5) is not significantly different from the global Na-22 radionuclide method (TSC = 49 +/- 6 mM, animals = 7).