Tethered photoacoustic capsule endoscope

Abstract

The primary motivation behind the advancement of optical-resolution photoacoustic endoscopy (OR-PAE) for clinical application is its unique capability to visualize capillary-level vasculature clearly. Indeed, this ability holds significant promise for gastrointestinal (GI) endoscopy because it can potentially contribute to diagnostic practices based on the visualized vasculature information. This relevance stems from the fact that early-stage malignant tumors often coincide with angiogenesis. Conventional OR-PAE devices implemented in a mini-probe format, however, presents a challenge when utilized in the context of the larger diameter of the GI tract. This challenge arises due to the blind spot phenomenon during imaging. Specifically, when applied to the GI tract with a considerably larger diameter than the mini-probe itself, certain target tissues fall beyond the effective working distance of optical focusing. Consequently, conducting efficient and comprehensive screening of the potentially suspicious segments within the extensive area of the GI tract becomes notably intricate. In order to address this challenge of blind spots inherent to conventional OR-PAE techniques, we developed a tethered OR-PAE probe with an 8-mm diameter and an encapsulated distal segment. This design adjustment yielded a lateral resolution of an impressive 10 μm—sufficient to resolve capillaries. Moreover, the B-scan imaging speed exceeded 20 Hz. By virtue of the encapsulated outer surface, the proposed configuration ensures that target tissues consistently fall within the predetermined working distance. Consequently, this study successfully demonstrates the acquisition of clear, in vivo 3D microvasculature images from a rat colorectum, spanning a full 360° angular region.