Development of a Virtual-Point-Detector-Concept Based Laser-scanning Optical-resolution Photoacoustic Micro-imaging System

• Main Authors: Yang, Che Chang, 楊哲昌
• Other Authors: Li, Meng Lin
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/76529476780650493845

碩士 === 國立清華大學 === 電機工程學系 === 104 === Recently, laser-scanning optical-resolution photoacoustic microscopy (LSOR-PAM) has been proposed to increase the 3D imaging speed; however, its use of a needle hydrophone or an unfocused ultrasound transducer for obtaining large field-of-view (FOV) compromises the signal-to-noise ratio (SNR). LSOR-PAM with an unfocused transducer also suffers the spatial impulse response (SIR) effect – the non-uniform piezoelectric response of the transducer to the photoacoustic sources in the FOV. The SIR effect also deteriorates the axial resolution and hinders the use of the high frequency broadband transducer required for spectroscopic applications. To solve these problems, we propose a virtual point detector concept for LSOR-PAM to improve the SNR and mitigate the SIR effect while retaining the imaging speed and minimizing the loss in the FOV. The focal point of a focused transducer is viewed as a virtual point detector which can be placed as close to the sample as possible to act like a real one even though the LSOR-PAM is with an optical and acoustic beam combiner. We preliminarily verify the feasibility of the concept by Field II simulation and existing ultrasound imaging system. Simulation results and experimental results both showed that there was a trade-off between the SNR and FOV determined by the distance between the virtual point detector and sample, which can be well tailored for different applications. The higher SNR than that of LSOR-PAM using an unfocused transducer could be obtained. Moreover, the suppression of the SIR effect was proven by A-line signals, spectrums and correlation maps. Comparison between the transducers with different center frequencies, in vivo micro-vascular imaging of a mouse ear and the preliminary results of a mouse brain were also drawn.