E. Hepatorenal Index (HRI)

For the calculation of the HRI, a B-mode image visualizing liver and kidney parenchyma through an intercostal sonic window was saved using the DICOM (Digital Imaging and Communications in Medicine)-format. To acquire this image, we always used the standard preset for abdominal ultrasound (convex probe with 4 MHz) with the gain control optimized by the machine. We then exported the image as a “Tagged Image File Format” (TIFF)-file with a resolution of 1280 x 960 pixels and analyzed it offline with the “ImageJ® ”-software developed by the National Institutes of Health (Bethesda, USA). This technique has been used in other scientific studies [16]. For the analysis, a round-shaped region of interest (ROI) with a diameter of 10 mm was placed in the kidney and liver parenchyma at the exact same image depth. Large vessels, bile ducts, focal liver lesions and kidney calyxes were avoided. Mean grayscale intensity in the ROI was measured with the software and the HRI calculated by dividing the mean intensity of liver by the mean intensity of kidney parenchyma (Fig. 2).

Measurement of the HRI in a 79 year old patient with S1-steatosis (fatty infiltration 30%, HRI 2.06).