Sonographic enhancement of renal cortex by contrast media

The purpose of this study was to evaluate whether a phase shift contrast agent could enhance the renal cortex. Four doses of the contrast agent EchoGen ranging from 0.25 to 0.65 ml/kg were injected intravenously in three healthy dogs. Images of the kidney were recorded on a videotape before and after each injection. The images were evaluated visually and were computer-analyzed for brightness change caused by the contrast agent. Marked changes in cortical brightness were observed at the doses of 0.45 and 0.65 ml/kg. At lower doses the changes in image brightness were significantly reduced but measurable. The brightness peaked at 65 +/- 9 seconds after injection and gradually decreased to the baseline value in approximately 12 minutes. The video density varied nonlinearly with dose, and at low doses its value drifted below the baseline. This is believed to be due to attenuation of echoes by the contrast agent. The results of this study indicate that the microbubbles formed by phase shift contrast media are sufficiently small and persist long enough to enhance sonographic images of the cortex. Contrast media whose effect is based on the phenomenon of phase shift permit enhancement of the gray scale characteristic of the kidney. The enhancements last up to several minutes and have strong potential to allow investigation of perfusion in kidney.