Abstract
A miniature all-optical probe for high-resolution photoacoustic (PA)-ultrasound (US) imaging using a large synthetic aperture is developed. The probe consists of three optical fibers for PA excitation, US generation, and detection of acoustic waves, respectively. The fiber for PA excitation has a large numerical aperture (NA) for wide-angle laser illumination. On the other hand, the fiber with a carbon black-polydimethylsiloxane composite coated on the end face of the optical fiber is used for wide-angle US transmission through laser-US conversion. Both the excited PA and backscattered US signals are detected by a fiber-tip Fabry-Perot cavity for wide-angle acoustic detection. The probe outer diameter is only ~2 mm. The synergy of the three optical fibers makes a large-NA synthetic aperture focusing technique for high-resolution PA and US imaging possible. High PA lateral resolutions of 104-154 μm and high US lateral resolutions of 64-112 μm over a depth range of > 4 mm are obtained. Compared with other existing miniature PA-US probes, to our knowledge, our probe achieves by far the best performance in terms of lateral resolutions and imaging depth range. The constructed probe has potential for endoscopic and intravascular imaging applications that require PA and US contrasts with high resolutions over a large depth range.
Highlights
Photoacoustic (PA) imaging forms an image based on optical absorption contrast with ultrasound (US) resolutions
Because the two imaging modalities receive the same signal form, acoustic waves, a PA-US dual modality system can be implemented by sharing the same acoustic detector
We describe a novel miniature dual-modality PA-US imaging probe consisting of three optical fibers for PA excitation, US transmission, and acoustic detection, respectively, to achieve high resolutions over a large imaging depth range
Summary
Photoacoustic (PA) imaging forms an image based on optical absorption contrast with ultrasound (US) resolutions. US imaging is based on acoustic backscattering to provide structural information. Both PA and US imaging has been demonstrated in a variety of biomedical applications such as ophthalmology [1], intravascular imaging [2,3], and smallanimal imaging [4,5]. The contrasts of PA and US imaging are complementary, which is useful to provide more comprehensive information. Because the two imaging modalities receive the same signal form, acoustic waves, a PA-US dual modality system can be implemented by sharing the same acoustic detector. Fiber-optic laser-US generation is promising because it can generate broadband wide-angle US and is easy for miniaturization
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