Large-depth-of-field optical-resolution colorectal photoacoustic endoscope

Defocus scanning, which causes a serious deterioration of the transverse resolution out of the focal zone, is a big obstacle to the application of optical-resolution photoacoustic (PA) endoscopy (OR-PAE) in imaging internal hollow organs. However, the current solution to generate an adjustable focal length is inapplicable for in vivo imaging due to the greatly increased scanning time. In this study, by applying an elongated focus lens that produces Bessel beams to the OR-PAE, we developed a large-depth-of-field optical-resolution PA endoscope with a depth of focus of similar to 8.6 mm in air, which can image targets at different depths without axial scanning, while maintaining a relatively constant transverse resolution. Ex vivo experimental results demonstrate the advantage of the endoscope to image biological tissues at different depths. Furthermore, an in vivo experiment presents three-dimensional vascular networks in the rabbit rectum, suggesting the potential of the endoscope for colorectal clinical applications. Published under license by AIP Publishing.