Synthetic aperture focusing technique for photoacoustic endoscopy.

Photoacoustic endoscopy (PAE) is a promising tool for the detection of atherosclerotic plaque. In this work, we propose a novel design of a side-viewing PAE probe based on a synthetic aperture focusing technique (SAFT) to enable high transverse resolution over large depth of focus (DOF) along the radial direction. A point-like ultrasonic detector is used to ensure a wide detection angle and thus a large synthetic aperture for SAFT. We first perform numerical simulation to optimize the PAE probe design, which involves the placement of the point-like detector and the diameter of a reflection rod mirror. Then, experiments are conducted based on the optimized probe design. High transverse resolution of 115-190 µm over large DOF of 3.5 mm along the radial direction is experimentally obtained. The SAFT-based PAE holds promise for endoscopic imaging with a high transverse resolution for both the surface and deep regions of tissue.