Miniaturized Endoscopic Probe for Photoacoustic and Ultrasound Molecular Imaging of Deep Tissues

Abstract

Colorectal cancer is a leading cause of cancer-related deaths worldwide. Traditional gastrointestinal endoscopes for colorectal cancer primarily relies on optical and ultrasound endoscopes. The former is limited to superficial tissue imaging due to significant light scattering in tissues, while the latter, despite deeper penetration, offers limited molecular imaging capabilities. In this work, we have built a miniaturized handheld photoacoustic/ultrasound dual-modality endoscopic probe to address these challenges. It has a small size of 8 mm, and offers the dual advantages of high penetration depth and superior molecular imaging capabilities, marking a significant advancement over traditional methods. Results show that this probe achieves a high lateral resolution of 345 μm for photoacoustic imaging and 185 μm for ultrasound imaging at a depth of 12 mm within tissues. It also exhibits the ability to effectively image complex structural targets, as demonstrated by the imaging of a phantom with an embedded metal mesh. Furthermore, the probe employs an innovative pump-probe method that effectively mitigates interference from blood and other background tissues, thereby enabling high-specificity photoacoustic molecular imaging. This capability is first confirmed by imaging the distribution of methylene blue (MB) in a phantom, and then demonstrated by the visualization of MB distribution deep within murine tumors. This handheld photoacoustic/ultrasound endoscopic probe, with its small size, high penetration depth, high spatial resolution, and superior molecular imaging ability, shows great promise as a vital diagnostic tool for colorectal and other gastrointestinal cancers. It can offer robust support for early diagnosis and treatment monitoring, potentially revolutionizing the detection and management of these diseases.