Miniaturized photoacoustic/ultrasound endoscopic imaging probe for molecular imaging of deep tissues

Colorectal cancer is one of the leading causes of cancer-related deaths worldwide. Traditional gastrointestinal endoscopes for colorectal cancer mainly rely on optical endoscope and ultrasound endoscope. Owing to significant light scattering in tissues the optical endoscope is limited to superficial tissue imaging, while the ultrasound endoscope, despite deeper penetration, provides limited molecular imaging capabilities. In this work, we build a miniaturized handheld photoacoustic/ultrasound dual-modality endoscopic probe to address these problems. It has a small size of 8 mm, and presents the dual advantages of high penetration depth and superior molecular imaging capability, marking a significant advancement over traditional methods. Results show that this probe achieves a high lateral resolution of 345 mu m for photoacoustic imaging and 185 mu m 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 adopts an innovative pump-probe method, which effectively mitigates interference from blood and other background tissues, thereby achieving high-specificity photoacoustic molecular imaging. This ability is first confirmed by imaging the distribution of methylene blue (MB) in a phantom, and then by observing the distribution of MB in the depth of tumor in mice. This handheld photoacoustic/ultrasound endoscopic probe has the advantages of small size, high penetration depth, high spatial resolution, and superior molecular imaging ability, and is expected to become an important diagnostic tool for colorectal cancer and other gastrointestinal cancer. This study can provide strong support for early diagnosis and treatment monitoring, potentially revolutionizing the detection and management of these diseases.