臺灣博碩士論文加值系統

一般臨床診斷上，常使用超音波作為臨床診斷的主要工具之一。超音波具有(1)非侵入性，(2)沒有輻射線，(3)即時掃描，(4)價格低廉等優點。因此近年來成為臨床血流量測的主要工具。尤其是在血流量測方面，超音波的即時診斷功能，更是目前臨床上其他儀器所沒有的特點。然而，當我們在量測都卜勒效應時，所量測到的都卜勒頻率會隨著都卜勒角（探頭軸向與血流流向之間的夾角）的增大而下降；所以一般量測都卜勒效應時，必須知道都卜勒角度，才能對流速做一正確的估測。一般臨床上進行都卜勒超音波血流量測掃描時，利用血管縱切面的二維超音波影像來設定都卜勒角度的值，並經由此都卜勒角度值估算真正的血流流速。此種方法須倚賴醫師的經驗才能對血流有一正確的量測。本研究的目的在於開發一種自動化的都卜勒角度與流速計算方法，我們結合傳統都卜勒量測軸向流速與橫向都卜勒量測垂直方向流速的特性，開發能夠應用於三度空間的流速量測方法。
在本研究中，我們主要是利用超音波中的都卜勒頻譜進行研究，我們量測傳統都卜勒的都卜勒頻移（縱向速度），與橫向都卜勒的都卜勒頻寬（橫向速度），並結合所估計出來的縱向與橫向速度，估測真正的速度。本研究首先是在血流模擬系統中進行，並進而推展到人體脈衝式血流流速量測上，最後應用此量測技術於小血管的研究上。此外，為了增進頻譜都卜勒的量測速度，我們開發短時間的頻譜運算方法，此方法利用最小平方方程式，求解頻率係數。此方法利用最小平方法解一序列的時間頻率方程式，所以能在很短的時間內估算量測訊號的頻譜。本研究利用頻域都卜勒開發自動化的都卜勒角度與流速量測方法，將來可進一步結合時間域的自動化都卜勒角度與流速量測方法，來增進估算的速度與臨床的應用。

In current clinical diagnosis, physicians often use Doppler ultrasound to be an important tool for blood flow measurements. Because ultrasound has the advantages of (1) noninvasive, (2) no radiation, (3) real time scanning, (4) low cost, it has been widely studied and discussed in recent years. Especially, the advantage of real time scanning of ultrasound is the characteristic that can’t be obtained in other medical instruments. However, when we use Doppler effect in measuring blood flow velocities, the measured Doppler frequency will decrease with the increase of Doppler angle (the angle between ultrasound beam axis and flow direction). Thus, in common Doppler applications, we always need to know the value of Doppler angle for flow velocities estimations. In current clinical blood flow measurements, doctors always use 2D ultrasound image to find the longitudinal cross-section image of blood vessel for Doppler angle determination. They correct the measured Doppler frequencies by the decided Doppler angle in order to estimate the actual flow velocities. This work highly dependents on the experience of doctors, and this is also time consuming to manually decide the Doppler angles. In this study, we want to find an automatic Doppler angle and flow velocity estimation method. We develop a flow velocity measurement method by combining the conventional Doppler and transverse Doppler theories. This method can be used for estimation the magnitude of 3D flow velocity.
In our research, we develop the flow velocity estimation method on spectrum Doppler. We measured the Doppler shift of the Doppler spectrum (axial velocity component) and the bandwidth of the Doppler spectrum (transverse velocity component). By combining the estimated axial and transverse velocity components, we can estimate the actual flow velocity. In this thesis, we applied our method in flow phantom measurements first. Then, we applied it in the measurements of human carotid vessels. We also applied it for small vessels measurements. Besides, in order to shorten the estimation time of the Doppler spectrum. We develop a short time spectrum analysis method. This method scans the frequency coefficients by solving a sequence of least square equations in a short time. In conclusion, a Doppler angle and flow velocity measurement method has been developed by using spectral Doppler. Future work will combine this method with the method developed in time-domain to improve the estimation efficient.

封面
誌謝
中文摘要
Abstract
Contents
1. Introduction
1.1 Medical Ultrasound
1.2 Pulse-Echo Imaging
1.3 Doppler Effect
1.4 Motivation
1.5 Importance of Blood flow Velocity Measurements
1.6 Research in angle independent flow Velocity Measurements
1.7 Dissertation Overview
2. Current ultrasound Blood Flow Velocity Measurment techniques
2.1 Spectral Doppler
2.2 Autocorrelation Method
2.3 Cross-Correlation
3. Transverse Doppler Theory
3.1 Transi Time Broadening effect
3.2 Geometric Broadening effect
3.3 Conclusion
4. Doppler angle and flow velocity estimation using combination ofconventional Doppler and transverse Doppler in constant flow measurements
4.1 Combination of conventional and transverse Doppler
4.2 Doppler spectrum of CFM-750
4.3 Constant Flow Measurements
4.4 Conclusion and Discussion
5. Implementation of spectral width Doppler in pulsatile flow
5.1 The difficult of spectrum averaging in pulsatile flow
5.2 Derivation of spectrum averaging process in pulsatile flow
5.3 Flow measurements in pulsatile flow
5.4 Conclusion and Discussion
6. Estimate Doppler angle and flow velocity of small vessel by spectral Doppler
6.1 The fd and fmax affected by smple volume size
6.2 Constant flows and pulsatile flows measurements in small vessel
6.3 Conclusion and Discussion
7. Short time spectrum analysis using time series least square solutions
7.1 Derivation of LSS method
7.2 LSS spectrum estimation for simulated data
7.3 LSS estimated spectrum for Doppler ultrasound signal
7.4 Conclusion and Discussion
8. Conclusion
8.1 Conclusion
8.2 Future Direction
Appendix

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