應用漏溢聲波波束成像技術進行即時影像導引

Abstract

在現今冠狀動脈疾病診斷中，X光血管攝影以及血管內超音波為臨床診斷的標準方式，然而在診斷過程中輻射以及顯影劑等對人體有害。為了取代X光攝影，本論文利用超音波系統連結電磁波追蹤系統與雷射，在導絲上經由雷射照射激發超音波導波，並利用先前研究中提出的漏溢聲波波束成型技術補償導波於導絲上傳遞時間，使影像在超音波系統上進行即時成像時正確回復導絲尖端位置，結合電磁追蹤系統的六個自由度(six degrees of freedom, 6DOF)資訊，將此尖端位置利用座標轉換放至研究中架設的空間位置，最後重建出導絲尖端的三維路徑。所提出的方法畫面更新率可以達到每秒14張左右，在尖端判定演算法部分，能在不同角度條件下準確偵測到導絲尖端，然而利用漏溢聲波的優勢在於即使因角度過大無法準確辨識導絲本體，漏溢聲波尖端的訊號基本上仍能依照所提出的尖端偵測方式進行判定。實驗結果的最大角度為56.31度遠大於傳統超音波影像，尖端平均方均根誤差為1.5mm。結合電磁追蹤系統進行重建三維導絲路徑的結果，在橫向掃描的實驗中得到導絲尖端移動距離平均誤差2.06mm，在仰角軸向掃描的導絲尖端移動距離平均誤差為2.61mm，對比於以X光方式進行的三維重建有相仿的誤差，具有取代現今X光血管攝影的潛力。

X-ray angiography and intravascular ultrasound are standard methods for clinical diagnosis of coronary artery disease, but the ionizing radiation and contrast medium are harmful to the human body. To replace the X-ray, we propose a new method for guidewire guidance by combining an ultrasound system, an electromagnetic tracking system, and a laser. Leaky acoustic waves (LAW) are generated by irradiating a laser pulse on the guidewire. Digital beamforming is then applied to perform real-time imaging of the guidewire. Combined with the six degrees of freedom (6DOF) data from the electromagnetic tracking system, the path of the guidewire tip can be determined after implementing coordinate transform. With the current setup, the frame rate can reach approximately 14 frames per second. According to our results, the maximum angle for the guidewire to be detected is around 56.31 degrees, which is larger than that achieved with traditional B-mode ultrasound imaging. The root means square error (RMSE) is 1.5 mm. The results of tracking of the guidewire path show that the mean errors are 2.06mm and 2.61mm, respectively. With similar errors for guidewire reconstruction with X-ray, the proposed method has the potential to replace X-ray angiography.