All-fiber photoacoustic endomicroscopy reveals layer-specific angiogenesis-oxygenation uncoupling in experimental colitis

Inflammatory bowel disease (IBD) progression involves complex microvascular remodeling and oxygen utilization disturbances that elude conventional endoscopy. We developed an all-fiber photoacoustic endomicroscopy (AFPEM) platform integrating high-density fiber-bundle scanning with broadband fiber-optic ultrasound detection, enabling high-resolution, fast dual-wavelength volumetric oxygenation mapping (7.7-μm lateral, 67.5-μm axial, 250-Hz B-scan rate). Serial quantification of vessel density, vessel width, hemoglobin, relative oxygen saturation (rsO 2 ), and oxygen extraction fraction (OEF) in colitis models revealed multilevel angiogenesis-oxygenation uncoupling: hypervascular expansion with elevated rsO 2 but reduced OEF during acute inflammation. Structural remodeling localized to the lamina propria (50 to 100 μm), whereas the peak diagnostic accuracy for mucosal healing, based on oxygenation, occurred at the crypt-associated layer (100 to 200 μm) with an area under the curve (AUC) of 0.899. Critically, although conventional endoscopy indicated mucosal healing and AFPEM associated vascular structural metrics had normalized, only rsO 2 accurately identified true tissue healing (AUC of 0.84, 95% confidence interval [95% CI]: 0.61 to 0.96). This technology provides a quantitative preclinical framework for vascular-metabolic biomarker development and supports future translational evaluation aimed at reducing unnecessary biopsies.