Photoacoustic Quantitative Flow Estimation Using Gold Nanoparticles

在本研究中，金奈米粒子被應用在分子光聲影像領域。光聲影像是一新進發展之影像技術，它結合了光學影像之高對比解析度及超音波影像之高空間解析度等優點。雖然有這些優點，光聲影像之應用到目前為止仍以組織型態之影像為主。我們的目的在於結合光聲成像技術以及奈米科技，建立出一套非侵入式、可觀測生物功能性影像的系統。在本論文之研究中，首先以Nd-YAG雷射波長532 nm之光束作為照射光源，中心頻率3.5 MHz之超音波探頭為聲波接收器，基於稀釋原理，以直徑40 nm之金奈米球做為光聲影像對比劑，進行定量流速估測，流量大小包括3 ml/sec、2.14 ml/sec、1.2 ml/sec、0.61 ml/sec、0.45 ml/sec、0.33 ml/sec以及0.23 ml/sec，以30毫升之空心球體當作待測系統，進行wash-out時間-強度曲線的量測；另一部分以Nd-YAG雷射1064 nm之光束為照射光源，中心頻率1 MHz之超音波探頭接收，以光吸收峰值為1018 nm之奈米桿為光聲對比劑，基於對比劑破壞-補充模型，進行wash-in時間-強度曲線量測，流速大小包括0.283 cm/sec、0.142 cm/sec、0.071 cm/sec、0.035 cm/sec以及0.018 cm/sec。比較各流速下時間-強度曲線中與流速相關參數與理論值的差異，在wash-out方式中，對比劑平均通過時間與理論值所計算之相關係數皆高達0.97以上；在wash-in方式中，計算所得流速與實際之流速之相關係數皆在0.96以上。在實際的應用，wash-out以及wash-in時間-強度曲線分別可以適用於不同的情況，但兩者的結果皆顯示了以時間-強度曲線法相對性流速量測之能力。在wash-out分析部份，空心球體的體積大小與輸入為瞬間注射的假設皆影響了此方法的實際應用，wash-in方法能夠改善以上的問題。此外，金奈米粒子濃度與光聲訊號強度之線性度，金奈米粒子對於光照射特性的差異，都影響了使用本方法在流速測量上的準確性。在未來工作上，將進行in vitro以及in vivo的實驗，靈敏度的提升以及生物相容性的驗證將是工作的重點。In this research, photoacoustic imaging techniques using gold nanoparticles are investigated. Photoacoustic imaging is a newly developed imaging technique. It combines the high contrast resolution of optical imaging and high spatial resolution of ultrasound imaging. However, the applications of photoacoustic imaging to date focus mainly on morphological imaging. Thus, constructing a non-invasive, blood flow related functional imaging system is the goal of this research. In the first part of this study, at first a pulsed Nd-YAG laser of a wavelength at 532 nm is used for laser irradiation and an ultrasound transducer of center frequency 3.5 MHz is used for acoustic detection (wash-out analyses). Based on the indicator-dilution theory, 40 nm gold nanospheres are used as the contrast agent for photoacoustic imaging. The actual flow rates are 3 ml/sec, 2.14 ml/sec, 1.2 ml/sec, 0.61 ml/sec, 0.45 ml/sec, 0.33 ml/sec, and 0.23 ml/sec. The mixing chamber of 30 ml is used. The wash-out time-intensity curve (TIC) is obtained to estimate the flow rate. In the second part of this study, a pulsed Nd-YAG laser of wavelength 1064 nm is used for laser irradiation and an ultrasound transducer of center frequency 1 MHz is used for acoustic detection (wash-in analyses). Based on the destruction-replenishment model, gold nanorods of absorption peak at 1018 nm are used as the contrast agent. The wash-in TIC is obtained to estimate the flow rate. The actual flow rates are 0.283 cm/sec, 0.142 cm/sec, 0.071 cm/sec, 0.035 cm/sec and 0.018 cm/sec. The flow parameters derived from the TIC among different flows rate are compared. The correlation coefficients between the mean transmit time derived from the wash-out TIC and the theoretical values are above 0.97. And the correlation coefficients between flow rates calculated from the wash-in TIC and the real flow rates are all above 0.96. Although wash-out TIC and wash-in TIC methods can be used in different applications, the results show that the wash-out TIC method is affected by the effective volume of the mixing chamber and the assumption of bolus injection. In practical applications, these issues can be resolved by the wash-in TIC method. The linearity between the concentration and signal amplitude of gold nanoparticles and the properties of gold nanoparticles under the laser radiation are also discussed for their effects on flow rate measurements. Future works will focus on improving the sensitivity for in vitro and in vivo applications. In addition, the biocompatibility tests of gold nanoparticles will be performed.第一章 緒論......................................................1 1.1 光聲成像原理簡介……… ……………………………………...1 1.1.1 光聲影像原理…………… ……………………………….....1 1.1.2 光聲成像目前之相關研究領域………………………………..3 1.2 光聲對比劑：金奈米粒子…………………………………………4 1.3 以對比劑輔助之血流量測…………………………………………5 1.4 指示劑-稀釋定理………………………………………………...7 1.5 破壞-補充模式…………………………………………………...9 1.6 研究動機………………………………………………………...11 1.7 論文架構…………………………………………………….....12 第二章 光聲原理與光聲對比劑.....................................13 2.1 光聲原理成像…………………………………………………….13 2.1.1 forward mode………………………………………………….15 2.1.2 backward mode…………………………………………………17 2.1.3 tomography mode………………………………………………17 2.2 光聲對比劑……………………………………………………….19 2.2.1 包覆染劑之微脂體 …………………………………………..19 2.2.2 與聚乙烯化二醇結合之染劑………………………………….19 2.2.3 金奈米粒子…………………………………………………….20 2.2.4 金奈米桿型變…………………………………………….....23 2.2.5 金奈米粒子在影像標定上之應用……………………………28 第三章 理論基礎……………………………………………………30 3.1 指示劑-稀釋定理…………………………………………………30 3.2 稀釋定理於實際應用上的限制………………………………….34 3.3 以雙能量雷射光之破壞-補充模型………………………………35 3.4 以單能量雷射光之破壞-補充模型………………………………38 3.5 Curve-fitting……………………………………………………40 第四章 實驗架構……………………………………………………………...41 4.1 Wash-out時間-強度曲線量測……………………………………41 4.2 使對比劑破壞之雷射能量臨界值決定………………………….43 4.3 wash-in時間-強度曲線實驗系統架設………………………….45 第五章 結果與分析…………………………………………………………...46 5.1 wash-out時間-強度曲線結果……………………………………46 5.1.1 MTT與 計算結果……………………………………………...46 5.1.2 不同體積之空心球體………………………………………….48 5.2 對比劑破壞之雷射能量臨界值……………..………………….49 5.3 雙能量wash-in時間-強度曲線結果………………………….…51 5.4 單能量wash-in時間-強度曲線結果…………………………….53 第六章 討論與結論…………………………………………………………...55 6.1 稀釋定理的可適用性…………………………………………….55 6.1.1輸入端為瞬間注射的假設……………………………………..55 6.1.2有效擴散體積………………………………………….……….56 6.2 破壞-補充模型中觀測波束寬度對流速估測之影響……………58 6.3 對比劑濃度與訊號強度之線性度……………………………….60 6.4 雷射光能量之安全規範………………………………………….61 6.5 使金奈米桿型變之雷射能量…………………………………….62 6.6 金奈米粒子特性之探討………………………………………….63 6.6.1 生物相容性…………………………………………………….63 6.6.2 奈米金奈子最低濃度之要求………………………………….63 6.6.3 樣本差異所造成之影響……………………………………….64 6.7 與其他影像系統之比較………………………………………….65 6.8 結論……………………………………………………………….66 6.9 未來工作………………………………………………………….67 6.9.1 以時間-強度法量測血液流速之應用………………………..67 6.9.2 金奈米粒子靈敏度的改進…………………………………….69 參考文獻………………………………………………………………7