以雷射都卜勒測速儀量測導波波傳行為並評估動脈假體剛性

Abstract

心血管疾病的診斷上動脈僵硬程度是一項非常重要的預測指標，近年來常見的臨床醫學診斷動脈硬化疾病主要以脈波傳遞時間與ABI指數作為評估指標。然而，上述兩種方法皆為間接式的評估指標，將無法反映真實動脈彈性性質，並且為全域式篩檢，無法進行特定區域局部性的動脈硬化篩檢。 因此，本研究提出以多層結構之動脈假體波傳理論，分別由薄板層、基底層與液體層等三層結構所組成，並求得其頻散曲線進而計算動脈組織之彈性係數。在實驗設計上，以外部氣體激發使產生表面波傳遞於動脈管壁表面上，以光纖式雷射都卜勒測速儀量測導波傳遞之振盪速度訊號，並且透過將探頭搭載於精密線性位移平台上，以多點式量測並計算相異位置感測點之時間差，進而計算得導波傳遞速度，將多個頻率之量測結果繪製與理論模型之頻散曲線，將其進行擬和求得其動脈管壁之材料彈性係數。 體外實驗量測分別以矽膠管與天然乳膠管模擬動脈組織並作為量測目標，以確認理論的可行性，為了能夠驗證量測之管壁彈性係數與真實彈性係數之誤差，本論文以AFM儀器針對軟性材料進行彈性係數量測，並與本研究之實驗量測之彈性係數進一步比較，體外實驗量測結果與真實之材料彈性具有一致性，且平均誤差分別為8.25%與7.14%。將上述分析方法應用於人體橈動脈實驗量測雖然在量測上操作不易，且仍然有許多改進空間，但結果仍就具有一定的可信度與應用可行性。 總結，本論文提出一套新穎的光學量測方法於檢測動脈彈性性質，於模擬人體動脈實驗已經得以驗證本論文所提出的方法，可以於未來應用於居家照護醫療裝置上，能作為心血管疾病的日常預防性篩檢。

Arterial stiffness is an important predictor to use when diagnosing cardiovascular disease. Recently, Pulse transit time and ankle branchial pressure index has been clinically identified as an index for evaluation of arteriosclerosis. Among these, pulse transit time is most often used in clinical medicine. However, the indirect method does not evaluate the actual material properties of arterial walls precisely, which may lead to misdiagnosis. Therefore, just considering pulse transit time is not suitable for evaluating arterial elasticity. In this research, we used a guided wave dispersion model to estimate the elastic properties of arterial phantoms. The theoretical assumptions were composed of a thin layer plate, the substrate layer and water-like fluid layer to simulate the blood vessels. In experimental setup, A fast air-puff valves was used to create a repetitive 80Hz to 200Hz low-frequency air-puff excitation to excite the guided wave propagation in the pipe wall. Polymer pipes were embedded in gelatin to simulate skin tissue and arteries. The system used a fiber-based laser doppler velocimetry to measure the velocity of the traveling waves on the pipe walls. Moreover, the probe was mounted on a linear translation stage and measuring the traveling waves velocity at multiple points. Then, the wave velocities were analyzed by the phase difference between the signal of different positions. The elastic property of the pipe was used to calculate the guided wave velocity by fitting a guided wave dispersion model. To verify the accuracy of this method, an atomic force microscope was used to measure the real elastic properties of the pipe and then compared to the proposed method. The prediction results of the silicon rubber pipe and latex pipe, the average error of the elastic modulus was found to be 8.25% and 7.14%. The results show good similarity and consistency of the two methods. And using the method to verify feasibility and accuracy of the elastic properties of radial arterial walls in vivo. In conclusion, we propose a novel technique for the assessment of mechanical properties of arterial walls in-vitro with high accuracy. Simulated experiments were performed to validate the proposed method. Our new proposed technique has been efficient to diagnose cardiovascular diseases more accurately for both home health care and for wearable devices.