Optically Transparent Focused Transducers for Combined Photoacoustic and Ultrasound Microscopy
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ORIGINAL ARTICLE
Optically Transparent Focused Transducers for Combined Photoacoustic and Ultrasound Microscopy Sunghun Park1 · Sungwoo Kang1 · Jin Ho Chang2 Received: 3 March 2020 / Accepted: 20 May 2020 © The Author(s) 2020
Abstract Purpose Photoacoustic (PA) microscopy has emerged as a useful tool in biomedical imaging applications such as visualization of microvasculature and hemoglobin oxygen saturation, single-cell, and label-free imaging of organs including cancer. Since the ultrasound transducers used for PA signal detection are not optically transparent, the integration of optical and acoustic modules for coaxial alignment of laser and acoustic beam fields in PA microscopy is complex and costly. Methods Here, we report a recently developed optically transparent focused transducer for combined PA and ultrasound (US) microscopy. All the acoustic layers including the acoustic lens are optically transparent, enabling simple integration of optical and acoustic modules for both imaging modalities. Results The mean light transmittance of the transducer’s backing layer and acoustic lens and of the transducer itself were measured at 92%, 83%, and 66%, respectively. Results from in vitro and in vivo experiments demonstrated the transducer to be suitable for both US and PA imaging. Conclusions The results of this study represent a step toward efficient construction of probes for combined PA and US microscopy. Keywords Optically transparent sensor · Photoacoustic signal detection · Photoacoustic microscopy · Ultrasound imaging · Hybrid imaging
1 Introduction Photoacoustic microscopy (PAM) has emerged as a useful tool in biomedical imaging applications due to its ability to provide anatomical and functional information with high spatial and contrast resolution. It can be used for imaging of microvasculature and hemoglobin oxygen saturation, single-cell imaging, and label-free imaging of organs including cancer [1–5]. Photoacoustic (PA) signals are generated from chromophores irradiated with laser and detected using an ultrasound (US) transducer. Hence, high-quality PAM imaging demands more sophisticated integration of optical and acoustic modules for coaxial alignment of the laser and * Jin Ho Chang [email protected] 1
Department of Electronic Engineering, Sogang University, Seoul 04107, Korea
Department of Information and Communication Engineering, Daegu Gyeongbuk Institute of Science and Technology, Daegu 42988, Korea
2
acoustic beam fields than cross-section PA imaging [6, 7]. Initially, an integration scheme based on dark-field illumination was used; an approach suitable for acoustic-resolution PAM (AR-PAM) [8] but not for optical-resolution PAM (OR-PAM). Use of a ring-shaped transducer enables removal of the optically reflective mirror placed around the transducer in dark-field illumination, supporting a more compact design suitable for OR-PAM [3, 9]. Since irradiating laser light can propagate through the opening in the transducer, laser energy loss is minimized. However, this configuration l
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