光聲薄膜結合光纖應用於雙模態液滴激發

Abstract

​微氣泡在超音波影像與治療中有許多應用，影像上基於強反射特性，可作為超音波顯影劑；治療上基於穴蝕效應、聲穿孔效應等超音波生物效應，則可作為藥物傳遞、血栓溶解或基因治療之藥物載體。然而微氣泡的穩定性與尺寸不盡理想，因此近年來奈米液滴日漸成為研究重點。奈米液滴不僅是在汽化後可與微氣泡具相同的功能，在汽化過程中的力學效應也可有其應用。相較於微氣泡，奈米液滴具有較高的穩定性、較小的尺寸。然而具有這些優勢的同時也代表液滴需要較高的能量來達到汽化。激發液滴汽化的方式可分為聲學激發與光學激發。研究顯示在光聲合併的雙模態激發下液滴汽化所需的總能量可大幅降低。然而現行的雙模態激發架構由兩套相互獨立的光學與聲學系統組成，需建立第三套系統將兩模態同步，硬體設備架構龐大。且當前研究皆以自由空間雷射作為導光途徑，難以將光導入體內。這些缺點對雙模態激發的實際應用造成限制。為解決架構複雜度與光路問題，本研究以單一光纖作為傳輸裝置。將雷射耦合到光纖中，以達到靈活快速的光路調整並允許光線被導入狹小空間。使用浸塗法製作光聲薄膜，藉由光聲效應，產生超音波，並將薄膜面積縮減製作於光纖出光口。透過調整薄膜的吸光度，使薄膜吸收光產生超音波對液滴做聲學激發的同時，也允許部分光源穿透，提供液滴光學激發所需光能，藉此免去超音波系統。另一方面，本研究從外觀型態、能量與頻譜，探討了薄膜暴露於雷射能量下狀態的變化。針對不同的薄膜製作參數以及重複浸塗次數，量測其聲場與光場的大小與分布，從中找出理想的薄膜輸出聲壓與光能。最後將薄膜應用於微氣泡的激發，由影像亮度與粒子顆數量化氣泡減少程度，作為薄膜具引發慣性穴蝕效應能力之驗證。最終將薄膜應用於奈米液滴的雙模態激發，透過粒徑分析證實其汽化能力。本研究做到使用單一光源產生超音波與光能量，縮減雙模態激發的硬體架構， 藉由將雷射耦合進入光纖，改善光路調整費時的問題，並使雷射與超音波能被引道入狹小腔室中，增加應用領域可能性。

Microbubbles have broad applications in diagnostic and therapeutic ultrasound. Due to their strong scattering, microbubbles can serve as contrast agents in ultrasound imaging. Based on ultrasound bioeffects such as cavitation and sonoporation, microbubbles can act as carriers for drug delivery, thrombolysis, or gene therapy. However, microbubbles are not ideal due to their instability and size limitations. Consequently, of nanodroplets have been developed. Nanodroplets not only function similarly to microbubbles after vaporization but also exhibit oscillatory behavior during the vaporization that can be utilized. Compared to microbubbles, nanodroplets offer higher stability and smaller sizes, but these advantages come at the cost of higher energy required for vaporization. There are two ways to induce droplet vaporization: acoustic excitation and optical excitation. Research indicates that dual-modality excitation using both acoustic and optical methods can significantly reduce the total energy required for droplet vaporization. However, current dual-modality excitation systems consist of independent optical and acoustic systems, requiring another system for synchronization. This results in a complex and bulky hardware setup. Additionally, laser used in current research is delivered in free space, which makes it difficult to guide light into confined spaces. These drawbacks limit the practical application of dual-modality excitation. To address these problems, this study uses single fiber as the delivery device. Coupling the laser into an optical fiber, achieving flexible and rapid optical path adjustments and allowing light to be delivered into confined spaces. A photoacoustic film was fabricated using a dip-coating method. Utilizing the photoacoustic effect, ultrasound is generated by the film, which is miniaturized and coated at the output end of optical fiber. By adjusting the film's absorption coefficient, the film absorbs light to produce ultrasound for acoustic excitation while allowing part of the light to pass through, providing the optical energy for droplet excitation, thus eliminating the need for an ultrasound system. Additionally, this study investigates the changes in the film’s morphology, energy, and spectrum under laser exposure. By measuring the acoustic and optical fields under different film fabrication parameters and number of repeated coatings, the ideal film output was determined. The film was then applied to microbubble excitation to verify its ability to induce inertial cavitation, quantified using ultrasound imaging and particle analyzation. Finally, the film was applied to dual-modality excitation of nanodroplets to demonstrate its vaporization capability, using particle analysis to determine the extent of vaporization. This study achieved the generation of both ultrasound and optical energy using a single light source, simplifying the dual-modality excitation hardware setup. By coupling the laser into the optical fiber, the issue of time-consuming optical path adjustments was resolved, and laser and ultrasound can be guided into narrow cavities, expanding potential application areas.