運用近場聲波偵測之光學掃描式光聲顯微鏡

本研究的目的在於設計一個微小且能高速取像的光聲顯微鏡。光聲影像系統為生醫影像的一支，主要探測人體組織吸收度形成對比。目前，光聲成像已廣泛應用在血管及血液的三維型態及功能性造影。前者可觀察腫瘤的血管新生或是創傷的血管癒合，後者則能監控血液中的血氧及血糖濃度，提供診斷和治療的依據；此外，光聲腦部影像和分子影像也有很大的發展潛力。光聲顯微鏡則是一種高空間解析度的光聲影像系統，它的解析度到達數個微米的等級，可用來取得組織中微血管的影像，甚至可以觀察單一紅血球的運動。然而，目前的光聲顯微鏡成像速度普遍較慢，而且空間及對比解析度受到共軛校準的影響甚鉅。本研究設計的目標為加速成像、系統微小化和提高解析度。這些技術在探針式光聲顯微系統設計，或是光聲顯微與其他影像系統整合中皆扮演關鍵角色。因此，在先導研究中，使用可調波長的鈦藍寶石雷射、單模光纖和 DVD 雷射頭組成光學系統，並用非聚焦探頭近場偵測光聲信號。對仿體進行造影測試，以探討系統的性能。首先利用毛髮仿體，可得橫向解析度約為 14.0um，而軸向解析度則有 50um 左右的水準，大約是30MHz超音波的波長。使用印刷的灰階仿體，發現經由 gamma 曲線修正後，光聲影像的對比與光學吸收度大致成線性，回歸係數為0.92。透過水聽筒測試，發現雜訊等效聲壓為 28.45Pa，與其他光聲顯微系統相仿。為了實現系統微小化和加速成像，本研究近一步採用 MEMS 技術的光學微鏡掃描子系統。此掃描鏡透過DSP微處理機及外部電路驅動和回授控制，可用 130Hz 以上的速度導引雷射光束，掃描樣品平面。在應用方面，則是演示了對於石墨型血糖試紙的非破壞性檢測。

關鍵字

生醫影像；光聲影像；近場超音波；光學顯微術；光學 MEMS

並列摘要

In this study, a miniature photoacoustic microscopy is designed for rapid image acquisition. Photoacoustic (PA) imaging is a biomedical imaging modality capable of creating images whose contrast is specific on optical absorption. Existing applications of PA imaging includes 3D visualization of vessels, arteries and blood flow. Under PA images, anatomical information such as tumor angiogenesis and vessel wound healing can be visualized. Besides, functional imaging of blood oxygen and sugar levels can also be performed for diagnosis and treatment purposes. Furthermore, PA brain imaging and molecular imaging have become rapidly growing fields. Photoacoustic microscopy (PAM) is a high-resolution version of PA imaging. With micron-order spatial resolution, PAM is capable of visualizing capillaries in tissues, even dynamics of a single RBC. Unfortunately, existing PAM designs suffer from low imaging speed. In addition, both spatial and contrast resolution depends crucially on the confocal alignment. The proposed solution in this study aims to accelerate image acquisition, minimize device size and improve resolution. Such design has great potential in probe-based PAMs, or an integrated multi-modality system including PAM function. In a feasibility study, we present a PAM based on single-mode fiber and DVD pickup head, in order to minimize the optics. Acoustic near-field detection is proposed, with which image resolution is solely determined by laser spot size and near-field behaviour of ultrasound. Phantom studies have been conducted to characterize the performance of this device. With a hair phantom, the lateral resolution is assessed at 14.0um. The axial resolution reaches 50um, corresponding to the wavelength of a 30MHz ultrasound frequency in water. The PA signal amplitude is approximately linear to optical absorption, with a 0.92 correlation coefficient, after fitting a gamma-corrected model. The noise equivalent pressure (NEP) of 28.45(Pa) is comparable to other PAM systems. To make PAM both smaller and faster, a MEMS optical scanning mirror is featured in this study. The mirror, which is controlled by DSP and an analog interface circuit, scans the laser beam across the specimen plane at a 130Hz speed. An application is demonstrated, where non-destructive testing is conducted on glucose test strips used in glucose meters.

並列關鍵字

biomedical imaging ； photoacoustic imaging ； near-field ultrasound ； optical microscopy ； MEMS optics

參考文獻

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運用近場聲波偵測之光學掃描式光聲顯微鏡

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