Sodium mapping in focal cerebral ischemia in the rat by quantitative (23)Na MRI.

PURPOSE: To validate (23)Na twisted projection magnetic resonance imaging (MRI) as a quantitative technique to assess local brain sodium concentration ([Na(+)](br)) during rat focal ischemia every 5.3 minutes.
MATERIALS AND METHODS: The MRI protocol included an ultrashort echo-time (0.4 msec), a correction of radiofrequency (RF) inhomogeneities by B(1) mapping, and the use of 0-154 mM NaCl calibration standards. To compare MRI [Na(+)](br) values with those obtained by emission flame photometry in precision-punched brain samples of about 0.5 mm(3) size, MR images were aligned with a histological three-dimensional reconstruction of the punched brain and regions of interest (ROIs) were placed precisely over the punch voids.
RESULTS: The Bland-Altman analysis of [Na(+)](br) in normal and ischemic cortex and caudate putamen of seven rats quantitated by (23)Na MRI and flame photometry yielded a mean bias and limits of agreement (at +/-1.96 SD) of 2% and 43% of average, respectively. A linear increase in [Na(+)](br) was observed between 1 and 6 hours after middle cerebral artery occlusion.
CONCLUSION: (23)Na MRI provides accurate and reliable results within the whole range of [Na(+)](br) in ischemia with a temporal resolution of 5.3 minutes and precisely targeted submicroliter ROIs in selected brain structures.