以超音波Nakagami影像與組織基頻諧波能量比定量生物組織散射子與介質特性

Abstract

因為具有即時性、非侵入性與較低的成本這些特性，使得不論在醫學上或研究用途上超音波影像被廣泛應用。可是單靠傳統B-mode影像不足以完整描述組織內部的情況，所以必須藉由一些參數來定量當組織內部發生的變化，本論文將針對組織內散射子與介質改變下，Nakagami參數與基頻諧波能量比兩種參數來定量分析。 藉由大白鼠肝臟纖維化實驗，發現在肝臟纖維化初期，病理切片分數同為0分時，Nakagami參數與用藥量的多寡呈現正相關；在大白鼠脂肪肝實驗的部分，也發現脂肪肝不僅組織的非線性程度發生變化，Nakagami參數隨著用藥量的增加也有上升的趨勢，並且把這些結果拿來與切片染色影像做比較。 根據過去的研究己知肝纖維化是組織內部散射子的增加，使用Nakagami參數的確可以判別纖維化的程度，而脂肪肝是組織內部介質的非線程度增加，使用Nakagami參數用於判別組織介質還不是那麼清楚，而動物實驗的結果也顯示了Nakagami參數不能細分組織性質。因此我們發展一套與Nakagami影像互補的方法，即基頻諧波能量比h/f，以同時區分散射子與介質特性之改變。 在仿體實驗中，分別改變散射子數目與改變脂肪含量的仿體來進行實驗，並將超音波逆散射訊號分別利用快速複立葉轉換(FFT)與經過經驗模態分解(EMD)後再做快速複立葉轉換後算出頻譜的基頻諧波能量比，發現仿體隨著散射子的增加h/f有下降的趨勢，仿體隨著脂肪含量增加h/f有上升的趨勢。而這結果正好補足了Nakagami參數的不足，未來若能在動物實驗也有正面的結果，則可望應用於臨床上。

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.