以Nakagami分布為基礎之三維定量超音波成像及其在生物組織上之應用

Abstract

今日超音波影像在各大醫院已經成為不可或缺的第一線診斷工具，是因為其具有非侵入式、人體無害、成本較低、機動性高與即時成像等優點。傳統上使用的超音波B-mode影像可用來檢測生物組織的內部結構，但不能完整能描述來自於組織內的真實情況，因此發展出許多有用的超音波定量方式來定量組織特性，在這些方法之中，Nakagami參數被證實應用在不同散射子濃度的偵測上有著顯著的能力。其後發展出以Nakagami參數為基礎的超音波Nakagami影像，更可將散射子特性視覺化。而為了改善Nakagami影像解析度並且包含更多的生物組織資訊，本研究將發展三維Nakagami影像。 在本論文中，我們將使用仿體實驗與離體纖維化大鼠肝臟之檢測，來探討三維Nakagami影像的可能性。我們需要從不同散射子濃度仿體的超音波逆散射訊號中，來求得最適當的三維Nakagami影像之計算方塊大小。結果顯示以八倍的超音波解析體大小來建立三維Nakagami影像是最合適的尺寸，在這狀況下二維Nakagami影像將得到更好的空間解析度。 接下來使用相同的方塊去計算不同纖維化程度的大鼠肝臟逆散射訊號，建立肝臟的三維Nakagami影像，並且比較不同纖維化程度的肝臟其Nakagami參數值與他們的Hematoxylin & Eosin和Masson's trichrome切片染色分析。結果顯示三維Nakagami影像確實可以分辨不同階段的肝臟纖維化，再者也增加了二維Nakagami影像的解析度並減少了subresolvable效應的影響，這是因為三維Nakagami影像提供了更多組織或是器官的資訊，將來該方式或許有潛力發展成為臨床診斷技術。

Nowadays, ultrasound imaging has become the most used clinical tool in hospitals. The ultrasonic B-mode image is used to examine the internal structures of the biological tissue. Due to the fact that the conventional B-scan cannot fully reflect the nature of the tissue, some useful quantitative method has been applied to quantify the properties of tissue. Among various possibilities, the Nakagami parameter was demonstrated to have an outstanding ability to detect the variation of the scatterer concentration. The ultrasonic Nakagami imaging based on the Nakagami parametric map has also been developed for visualizing the scatterer properties. In order to improve the Nakagami imaging resolution and involve more information from biological tissues, this study was aimed to further develop three-dimensional Nakagami image. In this study, phantom experiments and in vitro measurements on liver fibrosis were carried out to explore the feasibility of the three-dimensional Nakagami image. The ultrasonic backscattered signals were acquired from phantoms with different scatterer concentrations to evaluate an appropriate voxel size for constructing the three-dimensional Nakagami image. The result showed that the voxel with a volume corresponding to 8 times that of the transducer resolution cell is the most appropriate size for constructing the three-dimensional Nakagami image. In such a condition, the two-dimensional Nakagami image can get a better spatial resolution. We then used the same voxel size to create the three-dimensional Nakagami images of rat livers with varying degrees of fibrosis. Then we compare the Nakagami parameter values of different rat livers with their Hematoxylin & Eosin stain and Masson's trichrome stain results. The results showed that three-dimensional Nakagami image indeed can quantify different stages of liver fibrosis. Moreover, it has a better image resolution and also reduces the subresolvable effect of two-dimensional Nakagami image. In such a condition, the three-dimensional Nakagami image provided more information of tissues and organs, and it may have potential in future developments of diagnostic techniques.