Ultrasound Transducers by Using PVDF and PMN-PZT for Photoacoustic Imaging
- Abstract
- Photoacoustic (PA) imaging is a new developing imaging modality which has a potential for application in various areas, such as biomedicine and medical diagnosis. This imaging technology is a hybrid modality which combines the high contrast of optical imaging and the high spatial resolution of ultrasound imaging. It is based on the photoacoustic effect of materials or biological tissues, and it uses ultrasound transducers to detected laser-generated ultrasound signals for imaging. In PA imaging systems, ultrasound transducer is a very important part. Various kinds of transducers have been applied in these systems. Most of them are single element, linear array or curved array transducers. Several researchers have used circular array transducers to obtain high resolution images of tissue of small animals. However, the receiving sensitivity of the transducers is still not high enough for detection of weak PA signals.
The aim of this study is to develop the effective ultrasound transducers with high sensitivity in the frequency range of 1~10 MHz which is commonly used for low frequency PA imaging. In this study, piezoelectric PVDF films have been used to make a plane single element transducers and a 120-element circular array transducer. Besides that, piezoelectric single crystal PMN-PZT has been used to make a needle point transducer (or called needle hydrophone) and a circular array transducer with 120 needle hydrophones.
The pulse-echo response characteristics of the transducers were measured and compared. The results show that the PVDF single element transducer has center frequency about has a center frequency about 10.1 MHz and -6 dB bandwidth about 9.2 MHz (MHz, 91.1% fractional bandwidth). The PVDF circular array transducer has a similar center frequency (11.3 MHz) as the single element transducer. But it has a narrow -6 dB bandwidth about 5.7 MHz (50.4% fractional bandwidth). The PMN-PZT single element and circular array transducer have same center frequency about 6.2 MHz with a -6 dB bandwidth about 5.6 MHz (90.3% fractional bandwidth).
The receiving sensitivities of the fabricated transducers were compared. The PMN-PZT transducer shows a higher receiving sensitivity (Vpp = 90 mV) than the PVDF transducer (Vpp = 50 mV). The variation of the relative receiving sensitivity of PMN-PZT array transducer is about ±1.5 dB. For PVDF array transducer, the relative receiving sensitivity changes in the range from -47.1 dB to -37.9 dB. The PMN-PZT array transducer shows much better uniformity than the PVDF array transducer.
The fabricated transducers were applied to PA imaging systems. The single element transducers were used in a PA imaging system based on scanning acoustic microscopy approach. By comparing the obtained PA signals and PA images, it could be found that the PMN-PZT hydrophone has high PA receiving sensitivity and could obtained PA images with higher contrast than PVDF transducers. The PMN-PZT circular-array transducer was used in a PA imaging system based on tomography approach. The PA images were obtained with high resolution. Besides that, the influence factors of PAT imaging were discussed.
From this study, it is found that the PMN-PZT hydrophone shows much higher receiving sensitivity than the PVDF transducer. It obtained the PA image with higher quality than PVDF transducer. And the circular array transducer made by 120 PMN-PZT hydrophones can obtain PA images with high contrast. It has the potential to make image with higher resolution.
- Issued Date
- 2015
- Awarded Date
- 2015. 2
- Type
- Dissertation
- Publisher
- Pukyong National University
- Affiliation
- Department of Physics, The Graduate School, Pukyong
- Department
- 대학원 물리학과
- Advisor
- Kang Lyeol Ha
- Table Of Contents
- List of Figures iv
List of Tables vi
Abstract vii
1. Introduction 1
1.1. Background 1
1.2. Aims and Outline 3
2. Photoacoustic Imaging 5
2.1. PA effect 5
2.2. PA imaging system 8
2.2.1. Optical excitation 8
2.2.2. Acoustic detection 10
2.2.3. Reconstruction 12
2.2.4. Development of PA imaging system 12
2.3. Classification of PA imaging 16
2.3.1. 2-D PA imaging 16
2.3.2. 3-D PA imaging 18
2.3.3. Real-time PA imaging 20
2.4. Influence factors on PA imaging 21
2.5. Summary 22
3. Piezoelectric transducers for PA imaging 23
3.1. Piezoelectric transducers and PA imaging applications 23
3.1.1. Polymer transducer 23
3.1.2. Single crystal transducer 25
3.1.3. Ceramic transducer 27
3.2. Transducer fabrication for PA imaging 29
3.2.1. Single element transducers 30
3.2.1.1. PVDF transducer 30
3.2.1.2. PMN-PZT transducer 32
3.2.2. Circular array transducers 34
3.2.2.1. PVDF transducer 34
3.2.2.2. PMN-PZT transducer 37
3.3. Summary 38
4. Characteristics of the fabricated transducers 40
4.1. Pulse-echo response 40
4.1.1. Single element transducers 40
4.1.1.1. Experiments 40
4.1.1.2. Results 42
4.1.2. Circular array transducers 43
4.1.2.1. Experiments 43
4.1.2.2. Results 45
4.2. Receiving sensitivity 47
4.2.1. Single element transducers 47
4.2.1.1. Experiments 47
4.2.1.2. Results 49
4.2.2. Circular array transducers 50
4.2.2.1. Experiments 50
4.2.2.2. Results 51
4.3. Summary 54
5. PA imaging 56
5.1. Scanning acoustic microscopy approach 56
5.1.1. Imaging system 56
5.1.2. Experiment 58
5.1.3. Results 59
5.1.3.1. Single element transducers 59
5.1.3.2. Circular array transducers 63
5.2. Tomography approach 65
5.2.1. Imaging system 65
5.2.2. Experiment 67
5.2.3. Results 68
5.2.3.1. PA imaging using different number of elements 68
5.2.3.2. PA imaging using different size of pixel 71
5.3. Summary 76
6. Conclusions and future works 78
6.1. Conclusions 78
6.1.1. Characteristics of transducers 78
6.1.2. PA imaging 79
6.2. Future works 79
Acknowledgement 81
References 83
국문 요약 92
Appendix 95
A.1. Concave transducer 95
A.2. Fabrication of transducer 95
A.3. Characteristics of transducer 97
A.4. PA imaging 99
A.5. Summary 100
- Degree
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