Ultrasonic Vector Velocity Estimation in Swept-scan Using a K-space Approach
Date Issued
2005
Date
2005
Author(s)
Jeng, Geng-Shi
DOI
en-US
Abstract
The rapid developments in high-frequency ultrasound systems (operating at higher than 20 MHz) have allowed visualization of fine tissue structures and assessment of small vessels with slow flows. Due to the lack of high-frequency arrays, however, most current high-frequency systems use mechanically scanned, single-element transducers that are moved through a series of discrete positions. This scan technique, called the step-scan, is relatively time consuming and cannot provide flow information in real-time. An alternative technique, called the swept-scan, involves continuous scanning a transducer and is capable of improving the data acquisition time. Although the swept-scan technique is currently employed in high-frequency ultrasound systems, the continuous transducer movement may have nonnegligible effects on accuracy of velocity estimation. It is therefore the purpose of this thesis to thoroughly investigate such effects, and to further develop a new quantitative flow estimation method.
In this thesis, a spatial frequency domain (i.e., k-space) approach is employed to quantify the effects of swept scanning on the spectral-broadening-based vector velocity estimation method. It is shown that the k-space representation of a 2-D moving object is equivalent to a Doppler-RF frequency domain representation, and that transducer movement in the swept-scan technique results in a change in Doppler bandwidth. The spectral broadening caused by swept scan introduces velocity estimation bias and variance that are not present in the step-scan technique. In order to correct such effects and improve velocity estimation accuracy, a robust vector velocity estimation method is developed based on the proposed k-space approach. Both simulations and in vitro experiments were performed to evaluate performance of the proposed vector velocity estimator. Furthermore, in vivo measurements of mouse tail vessels were also conducted using a 45-MHz transducer. The results demonstrate that the proposed vector velocity estimator is feasible in swept scan and can effectively reduce the velocity and angle estimation errors.
The main contributions of the thesis include development of a theoretical framework for ultrasonic flow analysis using a k-space approach. Based on this framework, effects of the swept scan on flow estimation were thoroughly investigated, thus making quantitative flow analysis in ultrasonic small animal imaging more feasible.
Subjects
超音波影像
都卜勒超音波
血流估計
流速向量估計
掃掠式掃描
k-space
空間頻率
Ultrasonic imaging
Doppler ultrasound
high frequency ultrasound
blood velocity estimation
velocity vector estimation
swept scan
spatial frequency
Type
thesis
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