Improved Method for Calculating Hepatic Steatosis Using the Hepatorenal Index

Objectives-Marshall et al (AJR Am J Roentgenol 2012; 199:997-1002) initially demonstrated that the hepatorenal index is an effective and noninvasive tool to screen patients for hepatic steatosis. The aim of this study was to determine whether the hepatorenal index can be accurately calculated directly from a picture archiving and communication system (PACS) quickly and efficiently without the need for the multiple steps and specialized software used to calculate hepatorenal index in the study by Marshall et al. Methods-We evaluated 99 of the 101 patients included in the study by Marshall et al: patients being followed by hepatologists with plans for liver biopsy. The hepatorenal index was calculated by using Digital Imaging and Communications in Medicine (DICOM) images from a PACS and a markup region-of-interest tool. We compared this value to the value that Marshall et al derived by using specialized software and to standard histologic estimates. We created similar subgroups: patients with steatosis based on histologically estimated intracellular fat exceeding 5% and patients without steatosis. Results-The mean hepatorenal index +/- SD for those with steatosis according to histologic findings was 1.87 +/- 0.6, and for those without, it was 1.14 +/- 0.2. A hepatorenal index of 1.34 or higher had 92% sensitivity for identifying fat exceeding 5%, 85% specificity, a 94% negative predictive value, and a 79% positive predictive value. Substantial agreement was found between the hepatorenal index calculated from DICOM images and macrovesicular fat categorized at the cut point of 1.34 or higher (kappa = 0.76; 95% confidence interval, 0.62-0.88; P < .001). Conclusions-The hepatorenal index can be quickly and accurately calculated from DICOM images directly on a PACS without supplementary software.