Photoacoustic-photothermal visualisation of gastric tissues based on COMSOL

Photoacoustic Imaging (PAI) is a non-invasive imaging technology. It breaks through the limitation of shallow imaging depth of traditional optical imaging and low imaging contrast of acoustic imaging. It has a potential wide application in early cancer detection. PAI combined with endoscopy has great significance in the early diagnosis of gastric tumors. However, imaging just obtains the local location information. It cannot obtain the information of any location visually, especially in the process of photothermal therapy. In this paper, COMSOL was employed to simulate the visual model of photoacoustic photothermal imaging of gastric tissue and tumor. The physical processes of photoacoustic imaging such as photothermal strain-ultrasound generated by pulsed laser in stomach were simulated. A complete photoacoustic model was established through the coupling of each physical field. Firstly, a simplified gastric tissue model was constructed, and physical parameters were set for grid division. Then several physical field modules in COMSOL were coupled. The light distribution, temperature change and photoacoustic signal generated by thermal expansion during the propagation of light in biological tissues were obtained by simulation. The simulation results showed that the distribution of light in gastric tumor was significantly lower than that around the stomach. The tumor absorbs more light energy, resulting in a significantly higher temperature than surrounding stomach tissue. The photoacoustic signal of thermal expansion caused by laser irradiation of biological tissue was obtained. This study is helpful to understand the propagation and interaction of light in normal tissues and gastric tumors. It also provides a certain reference for the research and application of photoacoustic imaging in gastric cancer.