The effect of ultrasound parameters on the contrast ofTissue Harmonic Synthetic-spectrum Imaging

• Main Authors: Yi-Hsien Chu, 朱益賢
• Other Authors: Jen-Ho Tsao
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/59150346035504124823

碩士 === 國立臺灣大學 === 生醫電子與資訊學研究所 === 104 === Since the presentation of Nonlinear Acoustics has been proposed, the Tissue Har-monic Imaging has been widely used in clinical ultrasound diagnosis. The acoustic non-linearity parameter is larger in tissue lesion region than in healthy region and it conse-quently generates more harmonic energy. It can find the pathological changes easier in Tissue Harmonic Imaging than in Fundamental Imaging and hence results in the popular-ity of Tissue Harmonic Imaging. Nevertheless, there is still a lot of things that we can do better. The difficulty we find a pathological change in Tissue Harmonic Imaging is deter-mined by its contrast, spatial resolution, SNR, etc. Increasing pulse duration will improve SNR, but worsen the axial resolution. One way to improve this problem is using the Syn-thetic-Spectrum method. Synthetic-Spectrum Tissue Harmonic Imaging is emitting sev-eral narrowband pulses, taking the advantage of its long pulse duration to have abundant harmonic energy, and hence good SNR. After summing the narrow-band second harmonic signals they generate, it finally obtains a broad-band harmonic signal and then does im-aging. However, the contrast in Tissue Harmonic Imaging is even more important than the spatial resolution and SNR. If the tissue lesions did not appear clearly in the image, in other words, the image contrast is not enough, it will look like a Tissue Harmonic Imaging without lesions. It can use signal-to-interference ratio (SIR) to estimate the contrast of the image. Almost all ultrasound interference comes from sidelobe signal, so we can estimate the contrast by sidelobe level. Although Synthetic-Spectrum Imaging would improve the axial resolution and SNR simultaneously, its effect on the image contrast is still unknown. Therefore, the research purpose is to investigate the effect of the ultrasound imaging parameters to the sidelobe level of second harmonic signal at the focal length, and understand its effect on the image contrast. Finally, it will find the ultrasound parameters which optimize the image contrast.