Ultrasound-Based Hepatorenal Index (HRI): Measurement Principles, Normal Values, and Clinical Application

Ultrasound is a widely used, non-invasive, and radiation-free imaging modality that serves as a first-line diagnostic tool in hepatology due to its accessibility and real-time imaging capabilities. Recent advancements, such as shear-wave elastography and standardized techniques like the hepatorenal index (HRI), have improved the assessment of diffuse liver diseases despite their variable sonomorphologic presentation. The HRI is a quantitative ultrasound parameter that compares the echogenicity of the liver to that of the right renal cortex and serves as a non-invasive tool for detecting and grading hepatic steatosis. It is particularly useful in routine abdominal ultrasound due to its simplicity, reproducibility, and applicability without the need for additional equipment. Normal HRI values typically range between 0.8 and 1.2, with values above 1.4-1.5 suggesting hepatic steatosis, and values exceeding 2.0 considered indicative of significant fatty infiltration. Several factors influence HRI accuracy, including image quality, region of interest (ROI) placement, and equipment settings. While software-assisted analysis can improve reproducibility, standardization across devices and protocols remains a challenge. Future developments should focus on consensus-based measurement techniques and the integration of artificial intelligence to enhance diagnostic precision and clinical applicability.