Study On Principle And Technique Of Photoacoustic Scanning Imaging With Focal Transducer For Diagnosis Of Prostate Cancer

Photoacoustic imaging has recently emerged as a promising imaging modality for prostate cancer. This dissertation concerns about the imaging application of focused transducer with extended focal zone in the early noninvasive diagnosis of prostate cancer. According to a novel photoacoustic imaging technique for prostate, which adopted the internal light irradiation for photoacoustic excitation and a rectum-located focused transducer with extended focal zone for scanning photoacoustic signal, some studies has been systematic carried out, including light absorption distribution of prostate tissue, building and application of photoacoustic imaging system, etc. Innovations in the main research include the following five aspects.First of all, in order to understand light absorption distribution characteristics of different diffusing light source, help the optimization selection of excitation source and compensation of photoacoustic signal, a 3D complex optical model of human prostate by two diffusing light sources is constructed and combined with the Monte Carlo simulation method to provide the light absorption distribution. And their light absorption distribution patterns and irradiate range in the tissue model are compared with each other. Also, the light absorption difference of tumors is demonstrated based on a further-developed tumor-embedded-prostate model.Secondly, the dissertation pays attention to the time relation of light absorption at different position and photoacoustic signal generation. The author reconstructs the time-domain light distribution in the model based upon the Monte Carlo Simulation, and relative photoacoustic signal at different position is analyzed based on the theoretical relationship between photoacoustic signal and optical absorption energy. Relevant results are basically consistent with the experimental results, which confirm that the internal photoacoustic excitation in the advantage of improving depth imaging, and provide a further basis for excitation mode optimization in prostate photoacoustic imaging system. The simulation of photoacoustic signal maybe be used to simulate photoacoustic imaging and improve the detection accuracy and depth of photoacoustic imaging.Thirdly, according to the simulation results, the principle and method of a new type of photoacoustic scanning imaging technology for prostate are presented.The initial photoacoustic imaging experiment system is built, including urethral photoacoustic excitation model and the detection method of a rectum-located focused transducer with extended focal zone for scanning photoacoustic signal. The characteristics of the system are preliminary measured. Finally, experiments show that the imaging system has the capability of real-time monitoring of optical fiber insertion, which can be used to visualize the insertion process of the excitation fiber light source in order to ensure the appropriate depth of insertion.Fourthly, the dissertation proposes two types of internal excitation light source in the experiment of photoacoustic imaging. Our designed experiments demonstrate the imaging characteristic of the system, which shows the advantages of the proposed prostate photoacoustic imaging technology. The results also show that the side-firing light source help to imaging absorber of one side, and cylindrical diffusing light source can realize full range imaging. At the end, the imaging system is successfully applied to imaging experiments on real biological tissue samples, and then preliminary exploration of the application of this photoacoustic imaging in vitro canine prostate is made.Finally, a non-destructive method for absorber photoacoustic imaging and optical absorption coefficient simultaneous measurement is proposed based on a photoacoustic imaging technique by using internal light irradiation of diffuse light source. Since the absorption coefficient of tumor is closely related to its growth degree, and the two-dimensional scanning photoacoustic image can be used for determination the location and size of tumor, this method is particularly useful in the monitor and treatment of prostate cancer, providing accurate absorption coefficient for predicting the outcomes of photothermal interaction for cancer treatment with absorption enhancement in laser-induced interstitial thermotherapy.