剪切波彈性影像電腦斷層攝影

Abstract

剪切波彈性影像已在人體臨床診斷上開始被廣泛使用，其影像格式與B-mode超音波影像相同，因此這種掃描方式亦有助於彈性影像與B-mode影像的融合。而在本研究中我們提出一種新的掃描方式，希望能導入電腦斷層掃描之影像形式，以便能更適用於如三維細胞培養系統之應用。換言之，為求出剪切波速度分佈，我們提出以量測剪切波產生與偵測間之時間差來求得其飛行時間（time-of-flight），再搭配電腦斷層攝影之掃描與重建方法，便可計算出掃描範圍內的剪切波速度分布。此一方式所重建出之影像為平行於超音波探頭固定深度之切面，故相似於傳統光學顯微鏡之觀察方式，預期將更適於觀察三維細胞培養系統之彈性分佈。相較於一般傳統超音波成像，剪切波電腦斷層能接收不同角度的剪切波傳遞資訊，藉由不同角度、位置的掃描，可以降低在單一角度掃描所受到反射、折射等等之影響，有助於提升影像的正確性。在系統方面，在本研究中我們設計一個移動與旋轉平台，以探頭固定位置，移動放置於移動與旋轉平台上的樣本，以達成與電腦斷層攝影中探頭與樣本之間的相對運動，取得不同角度、位置的發射及接收資訊。在本研究中我們製作出三種結構的彈性影像仿體（軟硬各半、1.5mm寬度長條狀、直徑1.5mm橢圓狀），重建出剪切波速度分布影像，並分析影像重建的結果。實驗結果顯示剪切波彈性影像的可行性，未來工作將針對旋轉與平移機構之誤差，提出有效之降低方法，以近一步提升本方法之準確性。

Shear wave elasticity imaging has gained wide clinical acceptance. Its scan format is the same as that of regular ultrasound B-mode imaging, which also makes it convenient for image fusion with the corresponding B-mode image. In this research, we propose a new scan format by adopting the computed tomography approach so that it can be more suitable when imaging the elasticity distribution of a 3D cell culture system. In other words, by using the time-of-flight information between generation and detection of shear waves, the shear wave speed distribution can be calculated by using conventional computed tomographic reconstruction approaches. Such a scan plane is in parallel with the scanning plane of the ultrasound transducers during data acquisition; thus it is similar to that of conventional optical microscopes and suitable for observations of 3D cell culture systems. Compared to the conventional shear wave imaging approach, the proposed approach is expected to be more robust in the presence of unwanted reflection and refraction, as time-of-flight information from multiple angles is measured and used for reconstruction. We have constructed a shear wave computed tomography system in this research, and three different phantoms (half circle, 1.5 mm strip, and 1.5 mm cylinder) were used to test the performance of the proposed approach. Results demonstrate the feasibility of the proposed method, and the future work will focus on reducing errors due to the misalignment between the rotational and linearly translational stages.