超快超音波成像應用於連續非侵入式血壓量測

Abstract

心血管疾病是國人十大死因之一，其中，高血壓症是常見的心血管疾病成因，因此，監控血壓是非常重要的議題。此外，血壓也是常見的診斷指標，可以用來評估身體健康的狀況。目前量測血壓的方法有氣袖式血壓計、血壓探針等等。其中以氣袖式血壓計最為常見，其優點是非侵入式，方便簡單，不過缺點是只能量測到舒張壓以及收縮壓，無法計算連續且完整的血壓波型。血壓探針則是使用壓力感應裝置插入動脈中進行血壓量測，其優點是精密度高，而且可以量測連續血壓，缺點則是會造成疼痛，需要臨床醫師才能進行量測。為了非侵入式量測血壓，我們提出了使用動脈脈波速度量測相對壓力的方法。一旦相對壓力計算出來，絕對壓力也能隨之估計。為了驗證本理論，本研究使用塑膠血管仿體搭配血流幫浦系統並且使用超快超音波成像計算動脈脈波速度，計算出來的相對壓力在仿體與人體上分別和壓力傳感器與血壓計比較，得到了低於15%和20%的誤差。此外，本研究所計算出的絕對壓力則有高於50%的誤差，這樣的高誤差可以由剪力模數誤差來源分析解釋。當剪力模數有1kPa的誤差時，計算出的絕對壓力會有21mmHg的誤差。另外，本研究也有使用剪力波彈性影像量測不同靜態壓力下(25、40、80以及115mmHg)的剪力模數，結果顯示剪力模數隨著壓力呈現正向關係。要如何降低絕對壓力量測的誤差即為本研究之未來工作。

Cardiovascular disease (CVD) is one of the fatal diseases in Taiwan, and it may be caused by hypertension. Therefore, blood pressure monitoring is an important task to prevent CVD. The most common way to measure blood pressure is cuff-based sphygmomanometer, the merits of the method are convenient and non-invasive. However, it can only measure systolic and diastolic pressure. On the other hand, a pressure wire catheter is an invasive approach for continuous pressure measurements. However, it is invasive so it can only be performed by clinical physicians. To evaluate blood pressure non-invasively, we first proposed the use of pulse wave velocity (PWV) to evaluate the relative blood pressure. With the relative blood pressure, the absolute pressure can then be measured. To demonstrate this approach, carotid-mimicking vessel phantoms with a pulsatile pump and ultrafast ultrasound imaging was employed to estimate the PWV. Results of relative blood pressures in phantoms and humans measured by the proposed method show less than 15% and 20% respectively errors as compared with the relative pressures measured by a pressure sensor and a sphygmomanometer. Besides, results of absolute blood pressure measurements show up to 50% errors. The high errors can be explained by an error propagation analysis from the shear modulus estimation to the absolute pressure measurements. Specifically, a 1 kPa error in shear modulus results in 21 mmHg error of absolute pressure. In addition, results of shear modulus at different pressures (25, 40, 80 and 115 mmHg) measured by shear wave elasticity imaging show the positively correlated relationship between the blood pressure and the shear modulus. How to reduce errors in absolute blood pressure measurements is an important task for future work.