Optical-scanning Photoacoustic Microscopy with Acoustic Near-Field Detection
Date Issued
2012
Date
2012
Author(s)
Chen, Hsin-Yu
Abstract
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.
Subjects
biomedical imaging
photoacoustic imaging
near-field ultrasound
optical microscopy
MEMS optics
Type
thesis
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