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研究生：	柯銘揚 Ke, Ming-Yang
論文名稱：	建構多功能脈衝激發器於高頻超音波影像系統之應用 Development of a Multifunctional Pulse Generator for High Frequency Ultrasound Imaging System
指導教授：	陳天送 Chen, Tain-Song
學位類別：	碩士 Master
系所名稱：	工學院 - 生物醫學工程學系 Department of BioMedical Engineering
論文出版年：	2015
畢業學年度：	103
語文別：	英文
論文頁數：	44
中文關鍵詞：	高頻超音波影像系統、多功能脈衝產生器、任意波形產生器
外文關鍵詞：	high frequency ultrasound imaging system, multifunctional pulse generator, arbitrary waveform generator
相關次數：	點閱：139 下載：2
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本研究建構一套多功能脈衝激發器，包括短脈衝訊號(單極性負脈衝訊號與雙極性脈衝訊號)，以及編碼脈衝訊號。通常高頻超音波影像使用的激發訊號為短脈衝訊號(單極性負脈衝訊號)，雖然解析度良好，但是因為高頻的關係，應用於組織影像時，超音波訊號能量會大幅衰減，導致穿透深度及訊雜比不佳；進而發展出使用雙極性脈衝訊號，雖然能量有些許地增強，但因為頻寬下降，造成解析度也跟著下降；近年來為了更進一步改善高頻超音波衰減的問題，啾聲編碼波形開始被使用作為高頻超音波激發訊號，啾聲激發訊號透過拉長訊號長度，使其提升訊號平均功率去達成增加穿透深度及訊雜比的目的，但是拉長訊號長度的同時也降低了頻寬及解析度，所以在後端訊號處理的部分，將搭配壓縮濾波器，壓縮回聲波形以利於在增加穿透深度及訊雜比的同時，增加軸向解析度。多功能脈衝產生系統透過FPGA開發板搭配合適的高速DAC具有體積小、低成本、可重建修改適用於各種應用，且開啟一套提供研究者方便操作的平台，有助於未來超音波的研究與發展。在系統評估的部分，將呈現波形分析與頻譜分析，與市面上之儀器進行比較，得到媲美於商業儀器的效能，進而觀察回波的訊雜比與穿透深度之表現，編碼激發波形可得到優於短脈衝大約21dB的回波訊雜比與400%的穿透深度。最後評估成像表現，在壓縮濾波器的輔助下，編碼激發波形可在犧牲最小軸向解析度的前提下，大幅地增加訊雜比與穿透深度，達成我們所預想的結果。

This paper presents a development of a multifunctional pulse generator for high frequency ultrasound imaging system, which includes short pulse signal and coded pulse signal. Currently, the short pulse is commonly used in high frequency ultrasound imaging system since it has wide bandwidth with high resolution. However, the energy would severely attenuate while applying ultrasound tissue imaging. The attenuation will lead to the decrease of penetration depth and signal-to-noise ratio. Hence, to improve the effects of attenuation, bipolar pulse is developed. However, the decrease of bandwidth could deteriorate the system resolution. In recent years, chirp coded pulse is used as the excitation pulse for high frequency ultrasound imaging system to improve the attenuation of high frequency. By elongating signal length, chirp pulse increases mean power to improve the penetration depth and SNR. However, it would reduce bandwidth and resolution while elongating signal length. So, chirp pulse must work with pulse compression in back-end signal processing for increasing the penetration depth, SNR and resolution. This multifunctional pulse generator system is designed based on FPGA and high speed DAC which facilitates compact and cost-effective implementation. The reconfigurable structure is competent for various applications; moreover, it opens a platform for future research and development. When evaluating imaging system, waveform analysis and frequency domain analysis are presented; the system and the instruments for commercial use are compared. The efficiency of the system compares favorably with the instruments. Furthermore, the results show that the coded pulse signal can acquire 21dB increase of SNR and 400% increase of penetration depth in contrast with unipolar pulse. Finally, with the help of compression filter, chirp pulse can efficiently enhance the penetration depth with a minimal sacrifice of axial resolution.

CONTENTS
摘要	I
ABSTRACT	II
誌謝	IV
CONTENTS	V
TABLES	VII
FIGURES	VIII
CHAPTER 1 INTRODUCTION	1
1.1 Motivation and Objective	1
1.2 Literatures Review	3
1.2.1 Bipolar Excitation	3
1.2.2 Chirp Excitation	4
1.2.3 Multifunctional Pulse Generator	6
1.3 High Frequency Ultrasound Imaging System	8
CHAPTER 2 THEORETICAL BASIS	9
2.1 The Basic Principles of Ultrasound	9
2.2 Transducer	11
2.2.1 Axial Resolution	12
2.2.2 Lateral Resolution	13
2.3 Excitation Pulse of Ultrasound Imaging.	14
2.3.1 Unipolar Excitation	14
2.3.2 Bipolar Excitation	15
2.3.3 Chirp Excitation	16
2.4 Pulse Compression	18
CHAPTER 3 SYSTEM DESCRIPTION	19
3.1 High Frequency Ultrasound Imaging System Structure	19
3.2 Pulse Generator System	22
3.2.1 FPGA Control Core	22
3.2.2 High Speed DAC	24
3.3 Signal Processing System	26
3.3.1 Matched Filter	26
CHAPTER 4 RESULTS AND DISCUSSION	28
4.1 Pulse Analysis	28
4.1.1 Frequency Domain Analysis	28
4.1.2 Waveform Analysis	32
4.2 Signal-to-Noise Ratio Analysis	34
4.2.1 The SNR of Echo Signal	34
4.3 Penetration Depth	37
4.3.1 Tissue-Mimicking Phantom	37
4.4 Wire Phantom Images	40
CHAPTER 5 CONCLUSION	42
CHAPTER 6 REFERENCES	43
 
TABLES
Table 2.1 Acoustic Properties of Biological Tissues and Relevant Materials	9
Table 2.2 Average values of ultrasound parameters of bio-medical plastics	10
Table 4.1 The SNR comparison of different pulses	36
Table 4.2 The proportion of the tissue-mimicking phantom’s components	37
Table 4.3 The penetration depth comparison of different pulses	39
 
FIGURES
Figure 1.1 Schematics of the bipolar pulse generator	4
Figure 1.2 The ideal timing signals generated in the timing control circuit and the output of the bipolar pulse generator	4
Figure 1.3 The pulse echoes excited by bipolar and unipolar pulse	4
Figure 1.4 Schematic of the programmable modulated excitation imaging system	6
Figure 1.5 Block diagram of a multifunctional pulse generator	7
Figure 1.6 Unipolar pulse and their spectrum	7
Figure 1.7 35MHz bipolar pulse	7
Figure 1.8 60Vpp, 25 to 75MHz Chirp pulse	7
Figure 2.1 Direct piezoelectric effects	11
Figure 2.2 Reverse piezoelectric effects	12
Figure 2.3 The echo and imaging of high frequency ultrasound	12
Figure 2.4 The echo and image of low frequency ultrasound	12
Figure 2.5 The relationship between acoustic beam and lateral resolution	13
Figure 2.6 Unipolar pulse and its frequency domain analysis from MODEL 5900PR	15
Figure 2.7 Bipolar pulse and the frequency domain of bipolar pulse	16
from Tektronix AFG3252	16
Figure 2.8 Chirp pulse and the frequency domain of chirp pulse from Tektronix AFG3252	17
Figure 2.9 The compression echo signal by compression filter	18
Figure 3.1 System block diagram	19
Figure 3.2 The frequency response of pulse echo and the acoustic beam pattern	20
Figure 3.3 Altera DE2-70 development and education board	22
Figure 3.4 Block diagram of an arbitrary waveform pulse generator	23
Figure 3.5 The Altera DE2-70 development and education board	24
Figure 3.6 THDB-ADA, High-Speed A/D and D/A Development Kit	25
Figure 3.7 The chirp waveform from MATLAB and the schematic of data rate of DAC	25
Figure 3.8 The unipolar, bipolar and chirp waveform from FPGA	25
Figure 3.9 The original chirp and the reverse chirp pulse model	26
Figure 4.1(a) Model 5900PR (b) Tektronix AFG 3252	28
(c) The implemented multifunctional pulse generator	28
Figure 4.2(a) Unipolar pulse and frequency domain analysis from FPGA	29
Figure 4.2(b) Unipolar pulse and frequency domain analysis from Model 5900PR	29
Figure 4.2(c) Bipolar pulse and frequency domain analysis from FPGA	30
Figure 4.2(d) Bipolar pulse and frequency domain analysis from Tektronix AFG3252	30
Figure 4.2(e) Chirp pulse and frequency domain analysis from FPGA	31
Figure 4.2(f) Chirp pulse and frequency domain analysis from Tektronix AFG3252	31
Figure 4.3 The rising time (from extreme to zero voltage) and the convergence time	32
(the ringing of the pulse) of the unipolar pulse from FPGA and Model 5900PR	32
Figure 4.4 The symmetry and the convergence time (the ringing of the pulse)	33
of the bipolar pulse from FPGA and Tektronix AFG 3252	33
Figure 4.5 The unipolar echo signal from Model 5900PR	34
Figure 4.6 The unipolar echo signal from FPGA	34
Figure 4.7 The bipolar echo signal from Tektronix AFG3252	35
Figure 4.8 The bipolar echo signal from FPGA	35
Figure 4.9 The chirp echo signal from Tektronix AFG3252	35
Figure 4.10 The chirp echo signal from FPGA	36
Figure 4.11 The gelatin powder and the graphite powder	37
Figure 4.12 The tissue-mimicking phantom image of unipolar pulse	38
from Model 5900PR and FPGA	38
Figure 4.13 The tissue-mimicking phantom image of bipolar pulse	38
from Tektronix AFG3252 and FPGA	38
Figure 4.14 The tissue-mimicking phantom image of chirp pulse	38
from Tektronix AFG3252 and FPGA	38
Figure 4.15 The wire phantom and the detailed schematic diagram	40
Figure 4.16 The wire phantom image of unipolar pulse from Model 5900PR and FPGA	40
Figure 4.17 The wire phantom image of bipolar pulse from Tektronix AFG3252 and FPGA	41
Figure 4.18 The wire phantom images of chirp pulse from Tektronix AFG3252 and FPGA	41


                                    

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校內：2020-08-19公開
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