AJP - Renal Physiology, Vol 258, Issue 4 1125-F1131, Copyright © 1990 by American Physiological Society
Sodium-23 nuclear magnetic resonance imaging of the rabbit kidney in vivo
S. D. Wolff, J. Eng, B. A. Berkowitz, S. James and R. S. Balaban
Laboratory of Cardiac Energetics, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892.
The mechanism by which the mammalian kidney generates a concentration
gradient of sodium from cortex to papilla is still not entirely understood.
Studies of how the kidney as an organ generates this gradient have been
hampered by the lack of a noninvasive method for monitoring the intrarenal
sodium distribution. Herein, we demonstrate the value of sodium-23 nuclear
magnetic resonance (23Na-NMR) imaging to nondestructively assess the
intrarenal sodium distribution. 23Na-NMR images were obtained from a
surgically exposed kidney preparation that showed the two-dimensional
distribution of sodium in the rabbit kidney. In the antidiuretic kidney
this gradient resulted in papillary sodium concentrations that were
approximately threefold higher than cortical values. Serial 23Na-NMR images
obtained during saline infusion demonstrated the kinetics by which the
sodium gradient increases with diuresis. The half-time for 23Na washout of
the medulla of the kidney was approximately 6 min with this protocol. In
addition, a three-dimensional data set of the sodium distribution of the
kidney was obtained with voxel dimensions of 1.5 mm3 by use of a
three-dimensional 23Na-NMR imaging technique. Without surgical exposure,
23Na-NMR images of the rabbit kidney were collected under completely
noninvasive conditions by use of a surface coil. The 23Na-NMR signal from
the kidney was easily detected; however, to obtain images of comparable
signal-to-noise ratio to the surgically exposed kidney, spatial and
temporal resolution were significantly reduced.
