High Frequency Ultrasonic Flow Imaging
Date Issued
2005
Date
2005
Author(s)
Li, Chen-Han
DOI
zh-TW
Abstract
Small animal models have been used extensively in disease research, genomics research, drug development, and developmental biology. A non-invasive, small animal imaging system with high spatial resolution and high sensitivity is beneficial to the above-mentioned research. With such a system, the need to sacrifice animals can be reduced. The high frequency ultrasound imaging system (>20MHz) is ideal for such applications. However, one of the major limitations is the ability to detect slow and weak flows. A mechanical swept-scan technique is adopted in
our study, but the continuous movement of the transducer during data acquisition also potentially causes ambiguities in the Doppler spectrum. In addition, it is difficult to obtain high signal-to-noise ratio in this case
due to weak backscattering in micro circulation. Therefore, the main goal of this study is to improve the high frequency ultrasonic flow imaging on small animals in both areas. First, the scanning technique and signal
processing on color Doppler imaging for improvement of slow flow estimation is discussed. The swept-scan technique includes “block swept-scan” and “continuous swept-scan”. Continuous swept-scan with slow scanning velocity (2mm/sec) is found to be desired for slow flow
slower than 5mm/sec. On the other hand, contrast agents are used to enhance the signal-to-noise ratio and develop non-linear imaging methods. Liposome micro-bubbles are made in-house as the high frequency ultrasonic contrast agent. Based on in vitro results, it is shown that liposome bubbles can enhance the back-scattering signals in flow region at high frequencies (20~50MHz). The pulse-inversion based fundamental imaging technique is also tested to improve the contrast-to-tissue ratio. Compared to fundamental imaging, the contrast-to-tissue ratio can be
improved by 7~18dB. For the in-vivo experiments, on the other hand, the liposome bubble appears to break in the blood. So the contrast imaging of small animal is not as effective. The osmosis pressure is considered to be the major problem, and improving the effectiveness for in vivo flow imaging will be the primary future work of this research.
Subjects
小動物影像
都
卜勒
超音波
掃掠
式掃描
對比劑成像
微脂體
脈衝反相基頻成像
High frequency ultrasound
Small animal imaging
Doppler ultrasound
Swept-scan
Contrast imaging
Liposome
Pulse-inversion based fundamental imaging
Type
thesis
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