Assessment of ultrasound elastography to grade hepatic steatosis in a rat model

Objective To explore whether the non-invasive method of ultrasound elastography can diagnose and grade hepatic steatosis by using a rat model system.Methods Fifty healthy male Wistar rats were divided into a model group (n=40) and a control group (n=10) .The model was induced by high-fat diet (20% lard) , alcohol intake (10% in drinking water) , and CCl4 subcutaneous injections (40% in olive oil;0.2 ml/kg two times a week) .The control rats received normal diet, no alcohol, and olive oil injections.After weeks 6, 8, 10, 12, and 14 of the regimen, rats from each group were randomly selected and subjected to liver ultrasound elastography analysis (Hitachi HV900 Color Doppler instrument;6-13 MHz linear probe frequency) , first as transabdominal imaging then by fully exposed rat liver imaging, followed by pathological examination with hematoxylin-eosin staining.The imaging techniques were performed in triplicate for each rat and averaged.The imaging findings of controls (B) were compared to those of models (A) and used to calculate the strain ratio (B/A) .Hepatic steatosis detected by pathology was graded as percent of fatty degeneration: normal,<5%;mild,>66%.The correlations between B/A and pathology grades were assessed by Kruskal-Wallis and Spearman's coefficient tests.Results Ten rats died during the establishment of the hepatic steatosis model system.Of the 30 surviving model rats assessed by ultrasound and pathology, the hepatic steatosis grade was mild in 10, moderate in 12, and severe in 8;all control rats showed normal liver.The transabdominal imaging results (B/A) were significantly different between control rats (0.25±0.04) and rats with all three grades of hepatic steatosis (vs.mild: 0.43±0.05, moderate: 0.59±0.17, and severe: 0.89±0.21;P<0.05) .The B/A was positively correlated with the pathology grade (r=0.88, P<0.001) .Conclusion Ultrasonic elastography effectively diagnosed hepatic steatosis and was able to quantitate various pathologic grades in a non-invasive manner, suggesting its potential utility for clinical application.