The Research On Photoacoustic Tomography For Multi-layer Media Based On Frequency-domain Signal

Photoacoustic imaging which has the advantages of high contrast of optical imaging and high resolution of acoustic imaging is an emerging biomedical imaging technology.It has been widely studied in the field of biomedicine and has great application potential in the field of clinical medicine.Brain imaging has always been a key research theme of medical imaging,and it is also a hot spot of photoacoustic imaging in recent years.Photoacoustic transcranial imaging belongs to a branch of multi-layer media photoacoustic imaging which has got some research results.However,there are still some problems such as the difficulty and complexity for modeling the sound propagation process,the difficulty to obtain good imaging results because of the shortcoming of the algorithm.In this paper,a multi-layer medium model is constructed aiming at the related problems in photoacoustic transcranial imaging.The theoretical process of sound propagation and the construction of imaging algorithms are studied.Computer simulation and phantom experiments are designed to verify the theory and get certain results.The main research content and results of the thesis are as follows:(1)In this paper,The common experimental systems and commonly used algorithms in photoacoustic imaging are summarized,which can provide a reference for constructing multilayer photoacoustic tomography algorithms and the experimental system for phantom experiments.(2)A theoretical analysis of the process of the propagation for acoustic signal in the multi-layered medium is researched.The changes of the acoustic signal after the reflection and refraction of the acoustic signal passing through the interface between different media and the influence of the acoustic attenuation on the signal are mainly analyzed.The frequency-domain forward equation of photoacoustic signal propagation is derived,and the matrix model and linear equation system of photoacoustic signal propagation in multilayer media are constructed.Then,the imaging problem is changed into the problem of solving linear equation system.Last,the appropriate solution method is chosen.(3)Computer simulations were constructed to verify the algorithm theory,and the characteristics of frequency-domain photoacoustic imaging were studied.The simulation results show that the method has good reconstruction effects for absorbers in different shapes.The influence of frequency points on the imaging effect is studied,and the results show that the selection of frequency points should take into account the imaging time and imaging results.The imaging effects of our method were compared with those of the time-reversal method,and full width at half maximum and signal-to-noise ratio imaging quality for quantitative evaluation.Both qualitative and quantitative analysis proved the effectiveness of our method.Since the frequency domain signals are used for photoacoustic imaging,the matching pursuit algorithm is introduced for filtering to achieve a better imaging effect.The simulation and experimental results show that the matching pursuit algorithm can achieve a good filtering effect.(4)The phantom experiments are implemented to verify the constructed algorithm.Firstly,referring to the typical photoacoustic tomography system,the imaging system used in the laboratory is designed,and all the main equipment is carefully selected to satisfy the requirements of the experiment.Then,the reliability of the experimental system is verified.Finally,a three-layer medium phantom of the skull-like structure was designed to complete phantom experiments,and the reconstructed images were obtained and optimized.The experimental results are qualitatively and quantitatively analyzed and the reasons for the errors which can provide directions for the follow-up work are analyzed.