Xi Yang

Skulls with high optical scattering and acoustic attenuation are a great challenge for photoacoustic imaging for human beings. To explore and improve photoacoustic generation and propagation, we conducted the photoacoustic simulation and image reconstruction of the multi-layer brain model with an embedded blood vessel under different optical source types. Based on the optical simulation results under different types of optical sources, we explored the characteristics of reconstructed images obtained from acoustic simulations with and without skull conditions. Specifically, we focused on the detection of blood vessels and evaluated the image reconstruction features, morphological characteristics, and intensity of variations in the target vessels using optical and acoustic simulations. The results showed that under the initial PA signals, the types of optical source types corresponding to the strongest and weakest photoacoustic signals at different positions within the target region were consistent, while the optical source types were different in the reconstructed images. This study revealed the characteristics of acoustic signal transmission with and without skull conditions and its impact on image reconstruction. It further provides a theoretical basis for the selection of optical sources.

The human brain is a complex organ controlling daily activity. Present technique models have mostly focused on multi-layer brain tissues, which lack understanding of the propagation characteristics of various single brain tissues. To better understand the influence of different optical source types on individual brain tissues, we constructed single-layer brain models and simulated optical propagation using the Monte Carlo method. Based on the optical simulation results, sixteen optical source types had different optical energy distributions, and the distribution in cerebrospinal fluid had obvious characteristics. Five brain tissues (scalp, skull, cerebrospinal fluid, gray matter, and blood vessel) had the same set of the first three optical source types with maximum depth, while white matter had a different set of the first three optical source types with maximum depth. Each brain tissue had different optical source types with the maximum and minimum full width at half maximum. The study on single-layer brain tissues under different optical source types lays the foundation for constructing complex brain models with multiple tissue layers. It provides a theoretical reference for optimizing the selection of optical source devices for brain imaging.

Optical-based imaging has improved from early single-location research to further sophisticated imaging in 2D topography and 3D tomography. These techniques have the benefit of high specificity and non-radiative safety for brain detection and therapy. However, their performance is limited by complex tissue structures. To overcome the difficulty in successful brain imaging applications, we conducted a simulation using 16 optical source types within a brain model that is based on the Monte Carlo method. In addition, we propose an evaluation method of the optical propagating depth and resolution, specifically one based on the optical distribution for brain applications. Based on the results, the best optical source types were determined in each layer. The maximum propagating depth and corresponding source were extracted. The optical source propagating field width was acquired in different depths. The maximum and minimum widths, as well as the corresponding source, were determined. This paper provides a reference for evaluating the optical propagating depth and resolution from an optical simulation aspect, and it has the potential to optimize the performance of optical-based techniques.

Brain diseases need advanced detection methods to diagnosis abnormalities. Advanced imaging techniques have been developed and applied in different stages for several requirements related to anatomical, functional, and metabolic imaging for the human brain. Among them, photoacoustic imaging has the advantages of high resolution and deep penetration with rich optical contrast, which plays an important role in brain imaging. The characteristic of photoacoustic imaging brings the opportunity for different objects with multi-scale observation in the human brain. In this chapter, the authors introduce the principle and theory of photoacoustic imaging, review the modality of the present photoacoustic imaging systems and applications for brain diseases, and summarize the trends of this imaging technique.

The recent COVID-19 pandemic has caused tremendous damage to the social economy and people’s health. Some major issues fighting COVID-19 include early and accurate diagnosis and the shortage of ventilator machines for critical patients. In this manuscript, we describe a novel solution to deal with COVID-19: portable biosensing and wearable photoacoustic imaging for early and accurate diagnosis of infection and magnetic neuromodulation or minimally invasive electrical stimulation to replace traditional ventilation. The solution is a closed-loop system in that the three modules are integrated together and form a loop to cover all-phase strategies for fighting COVID-19. The proposed technique can guarantee ubiquitous and onsite detection, and an electrical hypoglossal stimulator can be more effective in helping severe patients and reducing complications caused by ventilators.

The recent COVID-19 pandemic has caused tremendous damage to social economy and people’s health. Some major issues fighting COVID-19 include early and accurate diagnosis and the shortage of ventilator machines for critical patients. In this work, we propose a closed-loop solution to deal with COVID-19: portable biosensing and wearable photoacoustic imaging for early and accurate diagnosis of infection and magnetically neuromodulation or minimally invasive electrical stimulation to replace the traditional ventilation. Proposed technique can guarantee ubiquitous and onsite detection, and electrical hypoglossal stimulator can be more effective in helping severe patients as well as reducing complications caused by ventilators.

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.