Research On Method Of Ultrasound Computed Tomography Based On Ultrasound Array

Ultrasonic tomography is a widely used non-destructive testing technology.It has broad prospects and great research value in engineering testing because it displays the internal structure and defect distribution of the detection object piece accurately,visually and completely in the form of an image.Conventional one-to-one placement of the ultrasonic probe arrangement has some problem such as frequently adjustment of the probe position,measurement errors.To solve this problem,ultrasonic probe placement based on linear arrays and wraparound arrays has become one of the research hot spots in the field of ultrasonic inspection.Wraparound array probe arrangement mode,the projection ray is sufficient for the detection object and has a good imaging effect,but the large amount of projection data leads to long calculation time,and the probe arrangement mode is greatly affected by the detection environment and the shape of the detection object.Linear array probe arrangement mode has a small amount of projection data and short calculation time,and the probe arrangement is less affected by the detection environment and the shape of the detection object,but the projection ray does not cover the detection object,and the imaging effect is not satisfactory.Therefore,the focus of this paper is find a way to improve the image quality when the projection data is incomplete,the main research work of the thesis is as follow:Firstly,this paper introduces the basic knowledge of the ultrasonic testing,the arrangement of probes based on ultrasonic arrays and the imaging equations of ultrasonic tomography,and then analyzes the ultrasonic tomography process based on imaging equations.Secondly,the ray tracing algorithm of ultrasonic tomography is analyzes.The improved LTI ray tracing algorithm based on expansion and contraction scanning is studied and the accuracy of ray tracing using this algorithm is verified by experiments.The commonly used ultrasonic tomography inversion algorithm and its characteristics are studied.For the commonly used inversion algorithm,the imaging effect is not ideal when the projection is incomplete.To solve this problem,this paper proposes a method to combine the improved SART algorithm with TV technology(improved SART-TV)to improve the quality of reconstructed images in the case of incomplete projection data.Experimental comparison of SART algorithms based on wraparound array data,SART algorithms based on linear array data and improved SART-TV algorithms based on linear array data.Observing the experimental results,we can find the improved SART-TV algorithm proposed in this paper can obtain better quality and more intuitive reconstructed image than the SART algorithm under the same conditions that projection data is incomplete.when the projection data is incomplete,and the validity of the image reconstruction algorithm when the projection data is incomplete is verified.In order to further improve the quality of reconstructed images,the paper studied the median filtering and BM3 D filtering,and found that the BM3 D filtering effect is better than the median filtering according to the experimental comparison.Finally,the BM3 D filtering and clustering analysis are combined to improve the SART-TV algorithm reconstruction.From the results of image processing,it can be found that the combination of BM3 D filtering algorithm and cluster analysis can well suppress the artifacts in the reconstructed image anh highlight the internal details,which has a good processing effect.