QUANTITATIVE TISSUE SODIUM CONCENTRATION MAPPING OF NORMAL RAT-BRAIN

A quantitative in vivo method for obtaining maps of tissue sodium conc entration (TSC) by MRI is compared to the invasive, global Na-22 radio nuclide dilutional technique in the normal rat brain, The NIR method u ses a three-dimensional projectional acquisition scheme to minimize si gnal losses from transverse relaxation, Internal calibration standards are used to convert the signal intensity into TSC after correction fo r B-1 inhomogeneities by using the ratio of Na-23 and H-1 images obtai ned with identical B-1 distributions and sensitivities at the two freq uencies, Over the biological range of concentrations, the TSC, measure d 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 us ing the MRI method (TSC = 45 +/- 4 mM, animals = 5) is not significant ly different from the global Na-22 radionuclide method (TSC = 49 +/- 6 mM, animals = 7).