Qualitative and quantitative comparison of renal vs. hepatic ultrasonographic intensity in healthy dogs

A prospective, cross-sectional study was performed to qualitatively and quantitatively compare the echogenicity of the renal cortex relative to the liver in healthy dogs. Twenty-five normal adult dogs were examined ultrasonographically. Three standard B-mode images (8.0 MHz) and three tissue harmonic images of the cranial pole of the right kidney adjacent to the caudate lobe of the liver were obtained. Renal and hepatic echogenicities were qualitatively compared by two observers. Subsequently, regions of interest (ROIs) were drawn in the renal cortex and the adjacent liver parenchyma at equal depths on each image, using two different ROI geometries: deep adjacent half-annular ROIs centered at the focal zone and small superficial adjacent squares placed in the near field. Renal and hepatic mean pixel intensities were quantified and averaged for individual subjects. Qualitatively, the right renal cortex was more commonly hyperechoic to liver. Quantitatively, the renal cortical mean pixel intensity was significantly higher than that of liver using deep half-annular ROIs, but not superficial square ROIs, for both standard (P = 0.0007) and harmonic (P = 0.0107) tissue imaging. These findings suggest that the renal cortex can be slightly hyperechoic to adjacent liver. The framework within which the canine renal cortical parenchyma is routinely evaluated in abdominal ultrasonography should be reconsidered, and mild hyperechogenicity relative to the liver (at 8.0 MHz) interpreted as a normal finding.