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Development of Optically Transparent Transducers for Ultrasound and Photoacoustic Image

  • 박성훈 (Sunghun Park, 서강대학교 일반대학원)

초록

Photoacoustic microscopy has emerged as a useful imaging method in biomedical applications due to their ability to provide anatomical and functional information in high resolution. Photoacoustic microscopy requires the integration of optical and acoustic modules for the coaxial alignment of the laser and acoustic beam fields. Because conventional ultrasound transducers as photoacoustic detectors are not optically transparent, this integration is complex and expensive. In this paper, an optically transparent focused transducer was developed by composing an optically transparent Lithium niobate (LNO)with a piezoelectric element, a backing layer, and an acoustic lens. The first schemes for combine of photoacoustic and ultrasound imaging were based on dark-field illumination for acoustic resolution photoacoustic microscopy, which is not suitable for optical resolution photoacoustic microscopy. For the coaxial alignment of the laser and acoustic beam fields, the optical fiber bundle was directly connected with the transparent ultrasound transducer to achieve coaxial alignment without additional acoustic and optical mirrors. The fabricated transparent ultrasound transducer was measured to have a center frequency of 11.2 MHz and a bandwidth of -6 dB of 23% in a pulse echo response experiment. All acoustic layers are optically transparent. In addition, the electrode used was also made of indium tin oxide transparent electrode. The average light transmittance passing through the transducer was measured as 55%. The optical properties of the developed transducer enable simple integration of optical and acoustic modules, and in vitro and in vivo experiments demonstrated that the transducer is suitable for acoustic resolution photoacoustic microscopy. The second transparent ultrasound transducer was developed as a transducer that was further developed from the first transparent focused ultrasound transducer. The developed photoacoustic microscope system delivered a laser to the object using a sophisticated objective lens in an optical bundle, and the ultrasound transducer was at a center frequency of 67 MHz, a bandwidth of -6 dB of 72% in a pulse echo response experiment. In addition, the lateral resolutions of the photoacoustic and ultrasonic images were measured as 33.8 μm and 67 μm, respectively. In addition, an image processing method using Laser induced Ultrasound was developed when the laser passes through the transparent ultrasound transducer and absorption occurs in LNO. Based on this, in vitro and in vivo experiments demagnetized that is the transducer is available for acoustic resolution photographic.

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목차

Chapter 1 Introduction 1
1.1 Background: Ultrasound and Photoacoustic Imaging 1
1.1.1 Ultrasound 1
1.1.2 Photoacoustic 4
1.2 Photoacoustic Microscopy 7
1.2.1 Optical Resolution Photoacoustic Microscopy 8
1.2.2 Acoustic Resolution Photoacoustic Microscopy 8
1.3 Thesis Motivation 9
1.4 Thesis Organization 10
Chapter 2 Introduction to Transparent Ultrasound Transducer 12
2.1 Introduction to Ultrasound Transducers 12
2.2 Transparent Ultrasound Transducer 16
2.2.1 Piezoelectric Element-Based Ultrasound Transducers. 17
2.2.2 Conclusion 24
Chapter 3 Optically transparent focused transducers for acoustic-resolution photoacoustic microscopy 28
3.1 Introduction 29
3.2 Design of Ultrasound Transducers 30
3.2.1 Design and Modeling Methods 30
3.2.2 Design of transparent ultrasound transducer 33
3.2.3 Finite Element Model Simulation Results 35
3.3 Fabrication of Transparent Ultrasound Transducer 36
3.3.1 Fabrication of Transparent Ultrasound Transducer 36
3.3.2 Light Energy Attenuation 37
3.4 Performance Evaluations 40
3.4.1 Pulse-Echo Response 40
3.4.2 Electrical Impedance 41
3.4.3 Beam Profile Experiments 41
3.4.4 Imaging Performance Evaluation 42
3.4.5 Spatial Resolution Experiments 44
3.4.6 In vitro Experiments 45
3.4.7 In vivo Experiment 48
3.5 Conclusion 51
Chapter 4 Optically Transparent Transducer with high frequency and new transparent electrodes 53
4.1 Thesis Motivation 54
4.2 New transparent Electrode 58
4.2.1 Ultrathin gold 58
4.2.2 Light Energy Attenuation 60
4.3 Design of Transparent Ultrasound Transducer 61
4.3.1 TUT frequency selection 61
4.3.2 Design of Transparent Acoustic Lens 62
4.3.3 Finite Element Model Simulation Results 64
4.4 Fabrication of Transparent Ultrasound Transducer 64
4.4.1 Manufacturing method of transparent ultrasound transducer 64
4.4.2 Light Energy Attenuation 67
4.5 Performance Evaluations 69
4.5.1 Pulse-Echo Response 69
4.5.2 Electrical Impedance 70
4.5.3 Imaging Performance Evaluation 70
4.5.4 Photoacoustic and Laser induced Ultrasound 71
4.5.5 Spatial Resolution Experiments 75
4.5.6 In vitro Experiments 76
4.5.7 In vivo Experiment 80
4.6 Conclusion 82
Chapter 5 Summary and Further Works 85
Bibliography 88

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