使用單一線性陣列探頭量測動脈脈波速度

Abstract

心血管疾病是國人十大死因之一，其死亡率逐年上升，而動脈硬化會導致許多心血管疾病，因此動脈硬化程度常作為心血管疾病的參考指標。脈波速度常用於評估動脈硬化程度，此速度可藉由血管的單一物理量變化來估計：量測血管兩處的物理量變化，由兩處之血管長度以及物理量變化波形的時間延遲估計脈波速度，即為foot-to-foot方法。傳統上，使用超音波估計脈波速度是以頸動脈與股動脈的血流或管徑變化估計主動脈的全域脈波速度；然而兩處的波形差異大，不利於計算時間延遲，而且血管長度不易得知，使脈波速度估計不準確，反觀單一動脈血管的局部脈波速度估計則可避免上述問題。由於超音波線性陣列探頭在臨床上已廣泛用於血管觀測，再者，隨著高速成像技術的發展，線性陣列探頭能夠有效地偵測局部脈波速度，將可提供方便的動脈硬化評估方法。 本研究利用高速成像技術，使用單一超音波線性陣列探頭發射雙波束取得血管信號，採用了廣泛用於超音波血流估計的都卜勒速度計算，取得血管管徑變化率，並以foot-to-foot方法估計脈波速度。為驗證此方法之可行性，以自製血管仿體模擬人體之頸動脈，進行體外的血流仿體實驗，並由Moens-Korteweg等式推測血管仿體之脈波速度理論值。體內實驗以人體之頸動脈為量測目標。 體外實驗結果顯示，使用雙波束可同時量測血管兩處的管徑變化率；然而，若欲準確估計脈波速度，則需改善實驗設置。在體內實驗中，以此方法取得兩受測者合理的脈波速度，分別約為4及5 m/s。

Cardiovascular disease is one of the ten most common causes of death in Taiwan and it is mainly caused by arterial stiffness. Pulse wave velocity is commonly used as it is directly related to arterial stiffness. Using the foot-to-foot method, pulse wave velocity can be estimated from pulse wave transit time between two measured locations with a known interval. Traditionally, the global pulse wave velocity between carotid and femoral arteries was estimated using two ultrasonic transducers. With the high frame rate imaging (>= 1000Hz), measurements of local pulse wave velocity with an ultrasonic linear array becomes possible. In this study, an approach based on foot-to-foot method to determine the pulse wave velocity is investigated. With dual transmit beams, the vessel boundaries at two measured sites with a known distance are recorded as a function of time. The pulse wave velocity can therefore be determined by estimating the time delay between the waveforms. To further improve estimation, a Doppler-based method widely used in color flow estimation imaging is adopted. Feasibility of the proposed technique was verified by conducting in vitro flow experiments. For this purpose, the carotid-artery-mimicking phantoms were made and the measured pulse wave velocity was compared to the value predicted by the Moens-Korteweg equation. In vivo measurements were performed on human carotid arteries. Our results of in vitro flow experiment indicate feasibility of dual-beam method. However, further refinement of the experimental setup is necessary. Moreover, reasonable results on pulse wave velocities (4~5 m/s) on two volunteers were obtained by our method in the in vivo experiments.