Transparent Ultrasound Transducer for Photoacoustic and Ultrasound Endoscopy to Improve Diagnostic Accuracy

Endoscopic ultrasound is a commonly used tool in gastroenterology for cancer diagnosis; however, it provides limited contrast in soft tissues and only offers structural information, which reduces its diagnostic sensitivity. To enhance this, numerous studies have tried to integrate photoacoustic technology with endoscopic ultrasound to improve tissue vasculature imaging, thereby boosting early cancer detection. The challenge, however, lies in achieving both high-quality photoacoustic and ultrasound imaging within an ultra-compact probe. For high-resolution imaging, both light and ultrasound need to be aligned in the same direction. Past attempts at this alignment have faced difficulties, with some strategies requiring drilling a hole in the ultrasonic transducer to secure the light path or tilting the optical system to align the two imaging paths. Both methods, though effective to some extent, resulted in compromises that could degrade the quality of either the ultrasound or the photoacoustic image.

A team of researchers from Pohang University of Science & Technology (POSTECH, Gyeongbuk, Korea) has developed the world’s first high-performance photoacoustic endoscopy utilizing a transparent ultrasonic transducer. In their study, published in the international journal Science Advances, the team has introduced an ultra-compact (1 mm²) transparent ultrasonic transducer that allows simultaneous high-resolution ultrasound and photoacoustic imaging. The transducer is built using piezoelectric material (PMN-PT), known for its high permittivity and miniaturization potential. Transparent materials like indium tin oxide electrodes and urethane sound-absorbing layers were used in the design, enabling the transducer’s structure to be maintained while allowing the light path to pass through. This innovative design facilitates the high-quality imaging capabilities of both ultrasound and photoacoustic techniques.

The team successfully integrated the optical and acoustic systems within this compact probe and aligned the imaging paths. To test the technology, they inserted the device into the channel of a commercial endoscope and captured images of a porcine esophagus. The images revealed clear visualization of all layers, from the esophageal mucosa down to the muscle layer, with ultrasound performance matching that of commercial endoscopes. Furthermore, they obtained high-resolution photoacoustic images from long distances, demonstrating the strong clinical potential of this photoacoustic-ultrasound endoscopy technology.

“This breakthrough is expected to overcome the limitations of existing photoacoustic-ultrasound systems and dramatically improve diagnostic accuracy,” said Professor Chulhong Kim of POSTECH.

“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,” added Professor Hee Man Kim of Yonsei Cancer Hospital.

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