超音波成像應用於血管內外血壓量測

Extravascular and Intravascular Continuous Blood Pressure Measurements by Ultrasound

李尚儒(Shang-Ju Lee)

指導教授 ： 李百祺

國立臺灣大學/電機資訊學院/生醫電子與資訊學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201903154

摘要

心血管疾病近幾年來是國人第二大死因，其中很重要的病因來自於冠狀動脈粥狀動脈硬化，當動脈粥狀硬化造成管徑顯著狹窄或是粥狀硬化斑塊破裂可能會產生急性血栓，進一步發生心血管危症。除了利用非侵入式方法測量血壓做初步心血管疾病的評估外，血管內壓力變化的情形可以更進一步提供可靠的動脈斑塊積累情況。本研究在血管外的實驗中，我們基於超快超音波系統針對回傳射頻訊號進行波束成像，並使用相位追蹤的方法來估算動脈脈波速度，最後根據我們提出的演算流程來得到連續血壓波型。為了驗證結果的正確性，我們製作塑膠血管仿體並搭配自行架設的血流幫浦系統來模擬脈波傳遞，並以壓力傳感器做為血壓計算的驗證，另外也實際收取了21位受試者的頸動脈影像進行壓力分析，與市售的血壓量測儀器相比誤差在3mmHg之內。在血管內壓力量測的實驗中，我們利用超音波模擬軟體Field II以及實際架設旋轉機構來模擬血管內超音波的運作情形，收取沿著旋轉方向的血流超音波射頻訊號，並針對不同角度的射頻訊號進行相關性比較，計算血液橫向位移以及探頭旋轉所造成的去相關斜率，在軟體模擬以及仿體實驗中的結果顯示流速與去相關斜率呈現正向的關係，可依此線性方程式來估算流速，最後搭配流體力學方程式來計算流體在血管中流經不同截面積的壓力損失，進而推算出血流儲備分數，了解動脈斑塊積累的情形。在仿體的驗證上，我們使用壓力傳感器紀錄血管阻塞前以及阻塞後的壓力變化，在不同壓力區間的實驗結果中顯示誤差約在5mmHg以下。由於本研究提出的血管內外血壓量測為估算的方法，並非像臨床有直接測量的儀器，會嚴重受限於壓力公式假設的影響，因此在臨床的應用上會有許多限制，未來仍須經過大量的人體實驗證明方法在臨床應用上的可行性。

關鍵字

血壓 ； 相位追蹤 ； 動脈脈波速度 ； 流體力學 ； 去相關斜率 ； 流速 ； 壓力損失 ； 血流儲備分數

並列摘要

Cardiovascular disease (CVD) has been the second leading cause of death in Taiwan in recent years. One of the most crucial issues of CVD is coronary atherosclerosis. When atherosclerosis causes significant stenosis or rupture of atherosclerotic plaque, acute thrombosis may occur and further increase the cardiovascular risk. The blood pressure can be measured extravascularly for cardiovascular disease assessment. In addition, the changes in intravascular blood pressure can also provide an assessment of the condition of arterial plaque. To this end, the primary purpose of this study is to develop extravascular and intravascular methods for continuous blood pressure measurements. In the extravascular experiments, ultrafast imaging was applied and a phase tracking method was developed to estimate the pulse wave velocity (PWV). Finally, the continuous blood pressure waveform can be estimated after considering the PWV and the elasticity properties of the blood vessel. The proposed method was tested both in vitro and in vivo. On human carotid arteries, it was demonstrated that the error was within 3 mmHg compared with that obtained from a commercial instrument. For the intravascular experiments, both numerical simulations and phantom experiments using intravascular ultrasound (IVUS) were performed. Results showed a positive correlation between the flow velocity and the signal decorrelation rate. After linear regression, the fitted velocity can be used to estimate the flow velocity and then the flow reserve fraction (FFR) based on the calculation of the pressure loss of a fluid flowing through different cross-sectional areas in the blood vessel. The error of pressure in this particular experiment was below 5mmHg. The intravascular and extravascular blood pressure measurements we proposed are limited by the hypothesis of pressure equations, unlike clinical used directly measuring instruments, there are many limitations and still need to been proved the feasibility in clinical application through a large number of human experiments.

並列關鍵字

blood pressure ； phase tracking ； pulse wave velocity ； fluid mechanics ； decorrelation rate ； flow velocity ； pressure loss ； fractional flow reserve

參考文獻

[1] V. L. Burt, P. Whelton, E. J. Roccella, C. Brown, J. A. Cutler, M. Higgins, M. J. Horan, and D. Labarthe, "Prevalence of hypertension in the US adult population. Results from the Third National Health and Nutrition Examination Survey, 1988-1991," Hypertension (Dallas, Tex. : 1979), vol. 25, no. 3, pp. 305-313, Mar. 1995.

[2] A. Benetos, F. Thomas, L. Joly, J. Blacher, B. Pannier, C. Labat, P. Salvi, H. Smulyan, and M. E. Safar, "Pulse Pressure Amplification: A Mechanical Biomarker of Cardiovascular Risk," Journal of the American College of Cardiology, vol. 55, no. 10, pp. 1032-1037, Mar. 2010.

[3] R. M. Carey and P. K. Whelton, "Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults: Synopsis of the 2017 American College of Cardiology/American Heart Association Hypertension Guideline," Annals of internal medicine, vol. 168, no. 5, pp. 351-358, Mar. 2018.

[4] A. V. Chobanian, G. L. Bakris, H. R. Black, W. C. Cushman, L. A. Green, J. L. Izzo, Jr., D. W. Jones, B. J. Materson, S. Oparil, J. T. Wright, Jr., and E. J. Roccella, "The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: the JNC 7 report," Jama, vol. 289, no. 19, pp. 2560-2572, May 2003.

[5] K. Narimatsu and K. Ohmori, "An algorithm for tonometric absolute blood pressure measurement," in Proceedings Computers in Cardiology, 1992, pp. 559-562.