Sodium magnetic resonance imaging of diuresis: Spatial and kinetic response

Abstract

Renal function is highly correlated with the sodium concentration gradient along the corticomedullary axis. The application of 3D high-resolution sodium magnetic resonance imaging (MRI) provided a means to quantify in vivo the spatial and temporal changes in renal tissue sodium concentration under normal and diuretic conditions. A detailed, pixel-by-pixel analysis of the intact rat kidney sodium MR images yielded a quantitative measure of the corticomedullary sodium gradient before and at early and later times after the administration of two distinct diuretic agents, furosemide and mannitol. Furosemide, a loop diuretic, induced a fivefold reduction in the cortical-outer medullary sodium gradient, whereas mannitol, an osmotic diuretic, did not affect this gradient. Both diuretics induced a 50% decrease in the sodium concentration of the inner medulla; however, mannitol exerted its effect twice as fast as furosemide with a 2.5-min exponential decay constant. These specific changes were attributed to the different mechanism of action and site of activity of each diuretic agent. Thus, high-resolution 23 Na MRI offers a unique, noninvasive tool for functional imaging of the kidney physiology. Magn Reson Med 53:545-552, 2005.

Using BOLD Imaging to Measure Renal Oxygenation Dynamics in Rats Injected with Diuretics

“…It is known that although furosemide inhibits the active transport that uses Na ＋ -K ＋ -ATPase, mannitol acts by an osmotic mechanism diŠerent from that of furosemide. 10 Because mannitol does not inhibit the active transport, as mentioned, it may have little eŠect on renal oxygenation. Although the predominant active site of mannitol has been reported to be the inner medulla, 10 the signiˆcant change in R 2 * was not observed in the inner medulla after mannitol administration in this study (data not shown), possibly because the change in the signal intensity of BOLD MRI after mannitol administration is very low in the inner medulla.…”

“…8,9 Furosemide is a powerful diuretic that acts on the thick ascending limb of Henle's loop 9 ; acetazolamide inhibits proximal tubular transport 8 ; and mannitol acts by an osmotic mechanism that washes out the high sodium concentration in the inner medulla through increased blood ‰ow. 10 Although the eŠect of furosemide on renal oxygenation has been well studied, 1,9 that of …”

Funktionelle MRT der Niere zur Erfassung strahleninduzierter Nierenschädigungen

“…Es konnte in tierexperimentellen Studien und in ersten Probandenstudien gezeigt werden, dass sich dieser Gradient unter physiologischer Belastung (Wasserbelastung, medikamentö-ser Diurese etc.) ändert und dies mittels 23 Na-Bildgebung dargestellt werden kann [8,17,18]. Somit erschließt sich potenziell Insgesamt liegen für die spezielle renale Fragestellung nur wenige Daten vor, insbesondere die in Klammer gesetzten Veränderungen sind nicht abschließend evaluiert.…”

Comparing anisotropic diffusion filters for the enhancement of sodium magnetic resonance images

“…Recently, Fermi filters were applied to sodium MRI to measure the sodium concentration gradient [8]. However, the increase in SNR by linear filters as previously proposed is paid by a loss in resolution, i.e., blurring the images.…”

“…A new emerging technique is sodium imaging of kidney [5][6][7][8][9][10]. It has great potential, as one of the main purposes of the human kidneys is the maintenance and the regulation of the fluid and electrolyte homeostasis [9].…”