沿圆弧形路径积分的反射式超声层析成像方法及实验研究

ULTRASOUND COMPUTER TOMOGRAPHY IN REFLECTIVE MODE OVER CIRCULAR ARC PATH AND ITS EXPERIMENTAL STUDY

讨论了近场及远场条件下沿圆弧积分的超声反射CT成像的重建算法 ,进行了计算机模拟成像 .在此基础上 ,建立了一套超声反射CT成像系统 ,对部分样品模型进行了实验成像 .

Ultrasonic B mode imaging has been widely used in the field of medical ultrasound diagnosis. A disadvantage of this technique is that it poorly visualizes objects lined up along the propagation direction of ultrasonic waves due to the weak reflection from objects hidden by objects in front. Furthermore, it suffers from limitations of lateral resolution due to beam width. S.J.Norton et al proposed an ultrasonic reflective tomographic method by a single transducer used for both emitting and receiving signals. This method has attracted high attention because of high resolution obtained both in axial and lateral directions and simplicity of measuring device. This method was used for observing planets and asteroids by T.K.Troung et al and they proposed a new reconstruction method to reconstruct the two dimensional image from projection data which is obtained from an integration of the reflectivity coefficients of the objects along the circular arc of the wavefront. In this paper, this extended version of the reconstruction method over circular paths for reflective ultrasound computer tomography (UCT) is discussed in the case of different distance between the transducer and imaged object. When the distance R between the transducer and the imaged object is much longer than the size of the object r, the curvature line of the integral can be approximately regarded as straight and the reconstructed two dimensional image can be obtained by using filtered convolution method similar to X ray CT. However, if the condition R>>r is not satisfied, the projection path is a circular arc and the reconstructed image can be obtained by iterative method. In the paper, some sample models with different R and r are proposed and two-dimensional images by computer simulation are obtained by filtered convolution method when R>>r and by iterative method when R>>r is not satisfied. Results of computer simulation coincide well with the sample models and the reconstructed error is also discussed in this paper. Besides, an experimental ultrasound computer tomography system in reflection mode is developed; two reconstructed images for sample models are presented in this paper. Our work suggests that, ultrasonic tomography in reflective mode will be prospective in ultrasound medical diagnosis and nondestructive detection and evaluation.