Miniature Probe for Forward-View Wide-Field Optical-Resolution Photoacoustic Endoscopy

Photoacoustic endoscopy (PAE), an ideal approach to enable internal organ and intravascular imaging, has to adopt a tailored scanner or scanning mechanism for 2-D or 3-D imaging. Forward-view endoscopy has found medical applications in gastrointestinal endoscopy and cystoscopy. Although recent works have demonstrated rotational scanning by using a micromotor or a rotational joint, they are not applicable to forward-view PAE. A micro-electro-mechanical systems mirror scanner has been used in forward-view PAE but suffers from the large probe diameter. Optical fiber bundles for either photoacoustic excitation or acoustic detection have been utilized for realizing forward-view PAE, yet the approaches have drawbacks in low resolution and a tradeoff between wide field of view (FOV) and probe miniaturization. Hence, the implementation of a miniature PAE probe capable of forward-view imaging with wide FOV and high resolution has remained a challenge. Herein, we present a miniature PAE probe (2.4 mm in diameter) capable of forward-view imaging with wide FOV (>3.5 mm in diameter) and high resolution (7.7-10.4 μm) through the use of an imaging fiber bundle, a gradient-index (GRIN) objective lens, and a fiber-tip Fabry-Perot ultrasound sensor with no scanner integrated into the probe. By incorporation of the GRIN lens, the FOV much larger than the probe diameter and high resolution can thus be achieved. The proposed approach is relatively simple and inexpensive. It may benefit applications in gastrointestinal endoscopy and cystoscopy by the forward-view capability with wide FOV and high resolution.