4:21 PM Abstract No. 32 Quantitation of hepatic fibrosis by ultrasound in diethylnitrosamine-induced rat model of hepatocellular carcinoma

The toxin diethylnitrosamine (DEN) causes stepwise progression of the hepatic inflammation-fibrosis-cancer (IFC) axis in the liver, providing for a rat model of hepatocellular carcinoma (HCC). This study aims to quantitate these liver changes using computer extracted grayscale ultrasound features in this DEN rat model of HCC. Fibrosis was induced in 7 male Wistar rats via ingestion of 0.01% DEN in drinking water for 12 weeks. Rats were imaged with ultrasound (US) at three-time points: baseline, 10 weeks, and 13 weeks. For each rat, 4-6 grayscale images were acquired from different lobes of the liver in standard imaging planes. US settings, including gain and time gain compensation, were kept constant for each imaging session. Images were analyzed quantitatively to measure echo-intensity level and 1st order histogram variance value (homogeneity level). Two-sample student t-test was used for comparison of data at the three-time points. Necropsy was performed after natural death or euthanasia. A sample of non-tumorous liver from 6 animals was sectioned and stained with hematoxylin-eosin and trichrome stains. Fibrosis was assessed using the METAVIR scoring system. Histology was correlated with final time-point imaging. Liver echo-intensity level across all rats showed an average increase from 42.9 at baseline to 56.4 at 10 weeks (p = 0.0013), reaching the level of 59.9 at 13 weeks (p = 0.0002) from DEN induction. Liver tissue homogeneity level (variance) showed an increase from 270 at baseline to 526 at 10 weeks (p = 0.0002) and 477 at the final time point (p = 0.0015). These changes corresponded to fibrotic changes on histology. The highest final echo-intensity level observed (67.1) corresponded with histology METAVIR grade F4, cirrhosis. The lowest final echo-intensity level recorded (54.3) corresponded with METAVIR grade F2, moderate fibrosis. Liver echo-intensity increased as time progressed in the inflammation-fibrosis-cancer cascade. Higher final intensities corresponded to greater fibrosis on histology. This quantitative radiologic correlation of liver fibrosis will be useful to evaluate background fibrotic changes accompanying rat HCC growth in future experiments.