Ultrasonic Synthetic Aperture Imaging by Angular Spectrum Analysis

• Main Authors: Twu, Jyh-Hwa, 涂志華
• Other Authors: Yin, Ching-Chung
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/36688552599119428223

碩士 === 國立交通大學 === 機械工程學系碩士班 === 85 === 　　The angular-spectrum-based synthetic aperture imaging method is studied in this thesis in an effort to improve the transverse spatial resolution of B-mode ultrasonic inspection. The standard fast Fourier transform (FFT) algorithm is adopted in this numerical scheme and is employed twice to obtain the spectra in time-frequency and spatial-frequency domains. The directions of wave vectors associated with the spatial frequencies are preserved in the process of image reconstruction. Compared to the conventional synthetic aperture imaging technique in time domain (so-called delay-and-sum method), the presented method features faster computing algorithm. In experiment a line focus immersion transducer with short focal length is used to approximate a small transducer transversely scanning at the focal point. It is obviously found that the transverse resolution in the far field was much improved. The near-field images were distorted because the wave fronts are not in the same cylindrical surface. This work is helpful in understanding the feasibility of a digital-typed medical ultrasonic scannign system.