Renal cortical ischemia in rabbits revealed by contrast-enhanced power Doppler sonography.

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Abstract
Our goals were to describe and quantify redistribution of renal cortical blood flow during systemic hypotension in rabbits using contrast-enhanced power Doppler sonography and to explore the feasibility of creating real-time regional blood flow maps of the kidney. Mild, moderate, and severe systemic hypotension (70%, 50%, and 40% of baseline measurements, respectively) were induced by controlled exsanguination in nine anesthetized rabbits. Sagittal power Doppler sonograms of the kidney were obtained during and after i.v. injection of 0.2 ml per kilogram of body weight of an experimental microbubble-based contrast agent. Doppler sonograms were analyzed for anatomic distribution of contrast agent and changes in mean pixel intensity over time. Cortical time-intensity curves were drawn and the area under the curve was compared with regional renal blood flow as measured by radiolabeled microspheres using linear regression in eight of the nine rabbits during graded hypotension. Graded hypotension resulted in increasing thickness of the nonperfused peripheral cortex (p < .001 by analysis of variance) with preservation of deeper cortical flow on enhanced Doppler sonograms. Other changes included decreased peak enhancement ratios and area under the curve values (p < .0001) and increased time to peak enhancement for cortex (p < .01). We found a strong correlation between cortical area under the curve and regional renal blood flow (r = .86, p < .0001). These changes were not shown without contrast enhancement. Peripheral cortical perfusion is disproportionately affected during systemic hypotension. Contrast-enhanced power Doppler sonography shows potential for depicting changes in regional renal blood flow in real time and without radiation.

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