Chronic liver
inflammation progressively evokes
fibrosis and
cirrhosis resulting in compromised liver function, and often leading to
cancer. Early diagnosis and staging of
fibrosis is crucial because the five-year survival rate of early-stage
liver cancer is high. This study investigates the progression of hepatic
fibrosis induced in rats following ingestion of
diethylnitrosamine (DEN). Changes in oxygen saturation and
hemoglobin concentration resulting from chronic
inflammation were assayed longitudinally during DEN ingestion by photoacoustic imaging (PAI). Accompanying liver tissue changes were monitored simultaneously by B-mode sonographic imaging. Oxygen saturation and
hemoglobin levels in the liver increased over 5 weeks and peaked
at 10 weeks before decreasing at 13 weeks of DEN ingestion. The oxygenation changes were accompanied by an increase in hepatic echogenicity and coarseness in the ultrasound image. Histology at 13 weeks confirmed the development of severe
fibrosis and
cirrhosis. The observed increase in PA signal representing enhanced blood oxygenation is likely an inflammatory physiological response to the dietary DEN insult that increases blood flow by the development of neovasculature to supply
oxygen to a fibrotic liver during the progression of hepatic
fibrosis. Assessment of oxygenation by PAI may play an important role in the future assessment of hepatic
fibrosis.