Photoacoustic Generation in Human Brain with Embedded Blood Vessel: Modeling and Simulation

Objective: Photoacoustics is a novel medical imaging modality based on optical excitation and acoustic propagation with high optical resolution and tissues penetration. However, the attenuation of the optical signal in the human brain due to the extinction caused by optical absorption and scattering leads to poor imaging performance. It is essential to explore the mechanism of the signal generation of photoacoustic imaging inside the human brain. Photoacoustic signal generation not only refers to the penetration and absorption of the light energy but also has the other processes contained heat transfer and thermal expansion to get the initial photoacoustic signal. Here, we modeled and simulated the photoacoustic signal generation in the human brain with an embedded blood vessel using finite element analysis.Methods: A model of the human brain was simplified into a 2-dimensional layer with a blood vessel embedded. The simulation was achieved using COMSOL Multiphysics. The processes of the simulation related to optical propagation and absorption, heat transfer, thermal expansion, and solid mechanical processes.Results: Based on modeling and simulation, we got the optical fluence and absorption, temperature, pressure with the excitation of a pulsed light source in various layers following the time. The results show that the optical energy in the shallow region is higher than in the deeper region, while the optical absorption and temperature increased differently from layer to layer. Although the optical energy arrived at the blood vessel is low, the energy acquired and temperature increase are higher than the horizontal direction. And the pressure change shows the photoacoustic signal generation of the blood vessel is obviously than the surrounding.Conclusion: We achieved photoacoustic signal generation in a model of the human brain using numerical simulation. The generation of a photoacoustic signal involved multi-physical processes with pulsed light incident into tissue and converted the light energy to increase temperature and to change the pressure. Significance: This research result helps to understand the mechanism of the photoacoustic signal generation inside a model representing the human head, which is a reference to prompt the imaging performance and improve the photoacoustic imaging technique for human brain imaging.