Photoacoustic Capsule Endoscope

Abstract

The key reason for developing an optical-resolution photoacoustic endoscopy (OR-PAE) in biomedical photoacoustics is its ability to provide capillary-level vasculature images, which is expected to be diagnostic in clinical gastrointestinal (GI) endoscopy—it is a cogent and important aspect because most malignant tumors are accompanied by angiogenesis in the early stages. However, conventional OR-PAE devices implemented in a mini-probe form suffer from the blind spot problem of imaging when applied to a GI tract with a much larger diameter compared to that of the mini-probe. It is natural because if a target tissue is located outside the working distance of the optical focusing, caused by a large variation of target distances, the relevant photoacoustic waves are not generated effectively like the effect of a limited depth of focus in an optical microscope, and thus making the intended rapid screening of the suspicious interval of a GI tract over a wide area very difficult. To overcome the blind spot problem of conventional OR-PAE, in this study, we developed an 8-mm diameter OR-PAE probe with a capsulated distal section. The achieved lateral resolution was as low as 10 μm, which is sufficient to resolve capillaries, and the B-scan imaging speed exceeded 20 Hz. As the capsular outer surface ensures that target tissues are situated at the set working distance, a clear in vivo 3D microvasculature image could be successfully acquired from a rat colorectum over a 360° full angular region.