The applications of coded waveforms in pulse inversion fundamental imaging
Date Issued
2006
Date
2006
Author(s)
Cheng, Yun-Chien
DOI
zh-TW
Abstract
In medical ultrasound imaging, micro bubble contrast agents are used to improve the contrast between blood perfusion region and soft tissue. Micro bubble oscillation produces stronger nonlinear response than tissue. Pulse inversion (PI) imaging excites two phase inverted pulses and sums the echoes to cancel the linearly propagated signal and keep the nonlinear components. The imaging keeping fundamental part of residue by filtering is called PI fundamental imaging. Generally, PI fundamental imaging has better contrast to tissue ration than traditional fundamental imaging and second harmonic imaging. In this research, we use chirp excitation, which is one of coded waveforms as an attempt to improve CTR by increasing pulse length and maintain the axial resolution by received pulse compression. In this study, chirp excitation is applied to pulse inversion fundamental imaging and the effects of pulse, acoustic pressure, bubble radius, and compression filters on imaging compression are discussed. However, because the compression filter is designed assuming linear propagation, the range side lobe becomes significant in PI fundamental imaging because the signal is from the nonlinear response. The less strict filter constraint produces less high frequency noise and lower range side lobe in compression. By linear compression, the axial resolution recovery of PI fundamental image is 50 % less than fundamental image. Chirps with big initial frequency change such as frequency increasing or broad bandwidth chirp produce strong PI fundamental signal. Contrast agents having more bubbles with oscillation radius scatter stronger nonlinear signal. All of these increase image CTR. To sum up, using contrast agents with oscillation radius, Gaussian chirps, having high amplitude, decreasing frequency, and broad bandwidth, and less strict constraint filter can get image with best CTR and axial resolution. Our future work will focus on single bubble experiments and alternative pulse compression filter design.
Subjects
微氣泡對比劑
脈衝反相基頻技術
壓縮濾波器
對比解析度
軸向解析度
Microbubble contrast agents
Pulse inversion fundamental imaging
Compression filter
Contrast to tissue ratio
Axial resolution
Type
thesis
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