Highly sensitive transparent ultrasound transducer for photoacoustic and ultrasound endoscopy in live pigs

Endoscopic ultrasound is widely used in gastroenterology for cancer diagnosis, but it offers limited contrast in soft tissues and only provides structural information, ultimately reducing diagnostic sensitivity. To address this, numerous studies have attempted to integrate photoacoustic technology with endoscopic ultrasound to provide more detailed information about tissue vasculature, thereby improving early cancer detection. However, achieving high-quality photoacoustic and ultrasound imaging simultaneously within an ultra-compact probe has proven challenging.

For obtaining high-resolution images, light and ultrasound must be aligned in the same direction. However, past efforts faced limitations in achieving this alignment. Ultimately, alignment could be achieved either by drilling a hole in the ultrasonic transducer to secure the light path or by tilting the optical system to align the two paths. Both approaches, however, come with trade-offs, often compromising the quality of either the ultrasound image or the photoacoustic image.

In this study, the research team developed an ultra-compact (1 mm²) transparent ultrasonic transducer capable of delivering high-resolution ultrasound and photoacoustic imaging simultaneously. To achieve this, they employed piezoelectric material (PMN-PT) known for its high permittivity and suitability for miniaturization. The transducer was constructed using transparent materials, including indium tin oxide electrodes and urethane sound-absorbing layers, which preserve the transducer's structure while allowing the light path to pass through. This design enables high-resolution ultrasound and photoacoustic imaging. The researchers successfully integrated the optical and acoustic systems within this ultra-compact probe and aligned the two imaging pathways.

To evaluate the technology, the team inserted the device into the channel of a commercial endoscope and captured images of a porcine esophagus. As a result, they were able to clearly visualize all layers from the esophageal mucosa down to the muscle layer, with ultrasound performance comparable to that of commercial endoscopes. Additionally, they obtained high-resolution photoacoustic images even at long distances, demonstrating the strong clinical potential of photoacoustic-ultrasound endoscopy.

Professor Chulhong Kim of POSTECH remarked, "This breakthrough is expected to overcome the limitations of existing photoacoustic-ultrasound systems and dramatically improve diagnostic accuracy." Professor Hee Man Kim of Yonsei Cancer Hospital added, "These successful experimental results with a transparent ultrasound transducer-based photoacoustic-ultrasound endoscopy system mark an important first step toward developing and localizing innovative diagnostic medical devices."

The research was conducted with support from the Basic Research Program of the National Research Foundation of Korea funded by Ministry of Education, the BRIDGE project of the National Research Foundation of Korea funded by the Ministry of Science and ICT, the Governmental Medical Device R&D Program and BK21 FOUR funded by the Ministry of Science and ICT, the Ministry of Trade, Industry and Energy, the Ministry of Health and Welfare, and the Ministry of Food and Drug Safety as well as the Deep Science Entrepreneurship Support Program provided by the Ministry of Science and ICT.