| Summary: | 博士 === 國立陽明大學 === 醫學工程研究所 === 88 === 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.
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