Regional T2 and sodium concentration estimates in the normal human brain by sodium-23 MR imaging at 1.5 T

We have analyzed multiple spin echo Na magnetic resonance (MR) images of the normal human brain in four volunteer subjects. Utilizing the much slower T2 decay of the CSF, we obtained images that separate cortex from the surrounding CSF and measured regional T2 of cortex, white matter, CSF, vitreous humor, and superior sagittal sinus. Assuming a sodium concentration of 145 mM in the vitreous humor, we normalized the extrapolated equilibrium magnetization (M0) for each region to the M0 of the vitreous humor to estimate regional sodium concentration. We found that regional T2 measurements more consistently distinguish the high signal regions of cortex, CSF, and blood than do our regional sodium estimates, whereas regional sodium estimates adequately distinguish white matter from cortex. The T2 values of white matter and cortex, on the other hand, are nearly identical. Our work addresses the problems encountered in establishing norms for clinical application of Na MR and represents a step toward establishing those norms.