Photothermal strain imaging for diagnosis of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) refers to the accumulation of excess fat in the liver without excessive alcohol consumption. Failure to detect NAFLD in advance can lead to fatal and irreversible liver diseases such as liver fibrosis, cirrhosis, and liver cancer, and thus the clinical need for rapid diagnosis of NAFLD is being raised. However, conventional NAFLD diagnostic methods, including biopsy and imaging, have inherent limitations due to technical or cost issues. For example, liver biopsy is invasive, MRI imaging is very expensive, CT is harmful for routine clinical use, and ultrasound is not very specific in diagnosing NAFLD. Here, we present photothermal strain imaging (pTSI), which uses the difference in thermal strain between fat and water during temperature change, as a new method for NAFLD diagnosis. The pTSI is a non-invasive, convenient, and cost-effective method of using a laser that matches the optical characteristics of the target. We developed a liver pTSI system to find fat accumulated in the liver using a clinical ultrasound imaging system and a lipid-sensitive continuous-wave laser. To demonstrate the feasibility of the pTSI system, in vitro experiments were performed using fat and chicken breast. The results showed that fat in the chicken breast was clearly distinguished. Finally, we performed in vivo experiments using NAFLD and normal rat. Through the difference in the strains that occurs when the laser heats the target, the progression of NAFLD could be determined.1