Theoretical And Experimental Study On X-ray Photoacoustic Imaging In Real-time Radiotherapy

Malignant tumor is a killer of human life,with the means of early treatment and early diagnosis increased,the clinical cure rate of cancer is rising.Radiotherapy,surgery and chemotherapy are important means of healing malignant tumors,of which about 2/3 of patients will receive radiotherapy.Using high-energy beam ionizing radiation,radiotherapy causes DNA double-strand breaks,leading to cell death.At present,the most important technique of clinical radiotherapy is image-guided radiotherapy,the tumor target volume is exposed to high-dose irradiation,avoiding the surrounding normal tissue and organs being irradiated by dose irradiation.At the present stage,the image-guided radiotherapy technique captures images at the setup,it adds additional dose to the patient,and can not monitor the relationship between tumor location and the beam in real time during radiotherapy.In view of this problem,this paper proposed the use of X-ray photoacoustic imaging to monitor the relative position of X-ray field and the target area in real-time during the process of radiotherapy,this method can reduce the additional dose.The basic principle of X-ray photoacoustic imaging is the periodic pulse X-ray irradiated on the material which make the material radiate ultrasonic wave due to thermal expansion,the transducer acquires of ultrasonic signals in the material side,use of image reconstruction algorithm to reconstruct the X-ray absorption of light distribution of the material.The main purpose of this paper is to explore the key factors that affect the quality of photoacoustic images,and provide the basis for multi-channel rapid acquisition through homemade transducers and photoacoustic signal acquisition experiments.Based on the K-Wave of Matlab toolbox,this paper completed the theoretical simulation,analyzed the main factors that affect the image quality of photoacoustic imaging,and designed the structure of the transducer array.(1)the atomic number of atoms,the greater the density and thermal expansion coefficient,the smaller the specific heat capacity,the material light absorption and thermal sound conversion higher,better image contrast.(2)The X-ray pulse width affects the photoacoustic signal generation efficiency and image resolution,and the image quality is better when the pulse width is 100 ns.(3)The transducer array design affects the image quality of photoacoustic imaging.The simulation results show that the number of transducer arrays is 128,the array area of the transducer is 10 mm and the radius of curvature is 500 mm.The design of the transducer array plays an important role in the completeness of the photoacoustic signal acquisition,which affects the image resolution.In this paper,different transducer array structures are set up,and the time inversion image reconstruction method is used to optimize the array design.In this paper,under the guidance of theoretical simulation,and the Shenzhen People’s Hospital of tumor radiotherapy experts,the use of single-channel photoacoustic signal acquisition system collected lead and water photoacoustic signal.Aiming at the low amplitude,low frequency and strong interference characteristics of the photoacoustic signal under the pulse width of 4us pulse,the electromagnetic interference in the radiotherapy environment was 15 d B,and the signal-to-noise ratio of the photoacoustic signal was 15 d B And the cost of the collected photoacoustic signal is increased by about 4 times,and the cost is reduced by about 10 times,which provides the basis for the physical design of the multichannel transducer.