Molecularly targeted photoacoustic endoscopy with fiber-scanning side-view probe for in vivo staging of early mucosal tumors.

Accurate in vivo staging of early gastrointestinal (GI) cancers is critical for selecting between local and systemic therapy. We present a molecularly targeted photoacoustic endoscopy (PAE) system that combines a compact, fiber-scanning side-view probe with a HER2-targeted near-infrared (NIR) contrast agent (KSP∗-IRDye800) to assess mucosal and submucosal tumor invasion in vivo. The 4.2 mm diameter probe uses a piezoelectric (PZT) bender to steer a laser beam laterally (±16°) and achieve high-resolution imaging. The system provides 363 μm lateral and 119 μm axial resolution at a depth of 3.1 mm and supports 3D volumetric image acquisition via rotational scanning and linear pullback. In vivo imaging was performed in CPC;Apc mice that spontaneously develop colonic adenomas. The targeted contrast agent demonstrated a significantly higher peak target-to-background (T/B) ratio (3.0 ± 0.3, RSD = 10 %) than indocyanine green (ICG, 1.37 ± 0.1), with peak uptake at 1.5 h post-injection. Adenoma dimensions measured by PAE correlated strongly with histology (ρ = 0.97 for width, ρ = 0.90 for depth), and 3D reconstructions accurately delineated tumor margins. Ex vivo validation confirmed imaging performance and molecular specificity. This work demonstrates the feasibility of targeted PAE for high-resolution, minimally invasive staging of early GI tumors. The system's resolution and depth performance are sufficient to distinguish between T1 and T1 lesions. Integration of molecular contrast with miniaturized photoacoustic imaging enables real-time assessment of tumor invasion depth and has potential to improve diagnostic accuracy and therapeutic decision-making during endoscopy.