| Summary: | 碩士 === 臺灣大學 === 應用力學研究所 === 98 === Ultrasound image is widely used for medical and research purposes due to many properties such as a real-time capabilities, non-invasive and low cost. But conventional B-mode image is not enough to describe the environment within the tissue , it is necessary to use some parameters to characterize when the tissue changes. This paper focuses on using Nakagami parameter and fundamental to harmonic energy ration to characterize when the scatterers and media change in tissue.
In the rat liver fibrosis experimental, the results show that there is a positive correlation between Nakagami parameter and dosage in the early stage of liver fibrosis when biopsy score is 0. Additionally, as can be seen from the rat fatty liver experiment, not only does the nonlinearity degree of the fatty liver tissue change, but its Nakagami parameter also increases with increase in dosage.
According to previous studies is known that liver fibrosis is the scatterers increases in the tissue, and the degree of fibrosis can indeed be determined by using Nakagami parameter. Fatty liver is due to the fact that the degree of nonlinearity of the tissue media increases. However, using Nakagami parameter to determine this increase is not fully developed. Animals experiments also showed that the Nakagami parameter can not distinguish when scatterers and media change in tissue. Therefore, we develop a complementary method with the Nakagami image, which is fundamental to harmonic energy ratio h/f, to distinguish the difference clearer.
In the phantom experiment, we change the amount of scatterers and fat content to experiment. We use the ultrasound backscattered signals to get the spectra after using fast Fourier transform(FFT) without and with empirical mode decomposition (EMD), and calculate the fundamental to harmonic energy ratio form the spectra. We found that h/f declines with increase of scatterers in the phantom, and h/f rise with increase of fat content in the phantom. These results exactly make up the shortage of Nakagami parameter. Moreover, in the future, if the animal tests show positive results, this method is expected to be used in clinic.
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