臨床前研究之剪切波彈性影像

Abstract

高頻超音波目前已經被廣泛應用在小鼠實驗上，提供臨床前研究了解各種小鼠疾病的模型及評估醫療器材的有效性及安全性。剪切波彈性影像為近年來在臨床上蓬勃發展的影像技術，因為可以提供即時量化的彈性結果，幫助醫生們做腫瘤硬化上的診斷。目前彈性影像系統還是以低頻超音波和臨床上的應用為主，而在高頻超音波系統上，並沒有用到剪切波彈性影像來量測組織彈性。因此本研究的目的在於高頻單一超音波探頭的系統上實現剪切波彈性影像，提供臨床前研究使用，量測小鼠肝臟彈性。高頻超音波除了可以提供高空間解析度，很適合用來觀測小鼠、細胞及皮膚等細微組織的結構上；相較於低頻超音波，還可以偵測到更小的剪切波位移、擁有更佳的剪切波訊雜比和可以量測到更硬的仿體組織。而傳統的低頻剪切波彈性影像系統，大多是使用陣列探頭，透過超聲速剪切成像(Supersonic Shear Imaging)的技術來成像，就可以很簡單的透過一個陣列探頭達到產生和偵測剪切波的功能，而我們所採用的系統是高頻單一探頭的超音波系統，不可能只使用同一顆探頭就可以達到同時產生和偵測剪切波。因此，為了在系統上實現剪切波彈性影像，本研究提出了系統時序同步設計和探頭共焦架構，讓推動探頭及影像探頭同步及藉由機械式掃描，透過自相關函數分析，得到剪切波位移，最後再由Time-of-flight及K-space的方法來重建彈性影像，成功的讓單一探頭系統達到類似陣列影像系統功能，可以同時具有高頻超音波及剪切波彈性影像的優點。仿體實驗結果顯示，本實驗架構系統可以量測到不同硬度仿體的彈性趨勢，且利用重建影像的方法也可以成功的把硬塊仿體的彈性影像重建出來。在小動物實驗之中，可以初步的量測出肝硬化與正常小鼠的肝臟彈性差異。

High frequency ultrasound has been widely used to investigate various mice models of diseases and to evaluate effect and safety of new health care technologies in preclinical studies. Recently, shear wave elasticity imaging has become an important imaging technique because it can provide quantitative results in real time to assist clinical diagnosis. However, most applications of elasticity imaging are currently only available on clinical array systems but not preclinical single element systems. Therefore, it is the purpose of this research is to design, implement and evaluate shear wave elasticity imaging on single element high frequency ultrasound system. High frequency ultrasound provides high spatial resolution which is not only suitable for observing microstructures but also better suited for the detection of smaller displacement resulted from shear wave propagation. Compared with conventional elasticity imaging systems using arrays, the main technical challenge of our system is the generation and detection of shear wave as arrays are not available for ultrafast imaging. Hence, a mechanical scanning system with confocal transducer design (one transducer for generation of shear wave and the other for detection of displacement) was proposed and implemented. By auto-correlation, we can calculate the shear wave displacement, and subsequently estimate the shear modulus using either the time-of-flight method or the k-space method. Performance of the proposed system was verified with both phantom experiments and in vivo mouse imaging with a liver disease model. It is concluded that the proposed system can be a new and effective tool in preclinical research.