Synthetic Spectrum Harmonic Imaging

• Main Authors: Yue-Feng Wu, 吳岳峯
• Other Authors: 曹建和
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/71085540988346657345

碩士 === 國立臺灣大學 === 生醫電子與資訊學研究所 === 99 === Tissue harmonic imaging has demonstrated that it can provide superior image quality compared to conventional fundamental imaging, contrast and spatial resolution can be substantially increased. Harmonic imaging has been used for detecting thyroid and breast. Harmonic generation mechanism of the acoustic wave propagates in tissues of the waveform distortion. However tissue harmonic intensity remains lower than that of the fundamental intensity, harmonic intensity is smaller than the fundamental intensity, so Tissue harmonic imaging suffers from the signal-to noise ratio(SNR) degradation, resulting in limited penetration depth . If there is a way can improve the harmonic signal SNR, Enhance the SNR could further improve the visualization of tissue at depth. Traditionally, the transmitted signal as a pulse in harmonic imaging, the pulse to obtain high-resolution images, the transmitted signal must be wideband pulse, but this will result in degradation of the transmitted energy. Coded excitation can improve the transmitted energy, it can enhance to harmonic signal SNR, but coded excitation could suffer from the increased sidelobe artifact, caused by the spectral overlap between the fundamental and harmonic components. So need to suppress the fundamental frequency through other methods. According to research, pulse inversion shows the best result to suppress the fundamental frequency, effective rejection of the sidelobe artifact. Coding excitation still has problems on the clinical. The problem is attenuation in tissue. So to be compensated on transmit and receive, however coding excitation hard to compensate. In my research, synthetic spectrum also can improve the harmonic signal SNR. It’s important to compensate easily. In Synthetic Spectrum, more pulses are transmitted with different frequencies. Use a Band-pass filter to get harmonic components. Sum of harmonic signals is synthetic spectrum. In fact different frequency harmonic signals will attenuate in the tissue. The main reason for attenuation is Transducer and tissue. Narrow bandwidth of transmission signal can be regarded as constant coefficient compensation. This paper will explore the basic principles of synthetic spectrum for further to improve.