New Technology - Germany Develops Ultrasound Probe with Super-Resolution Imaging

Researchers from the Helmholtz Zentrum München and the Technical University of Munich (TUM) in Germany have developed the world's smallest ultrasound detector based on miniature photonic circuits on silicon chips. This new detector is 100 times smaller than the diameter of an average human hair. With it, many features far smaller than before can be visualized, achieving what is known as super-resolution imaging.

Chip with multiple detectors (approximately 3mm x 6mm in size). The fine black engravings on the chip surface are the photonic circuits connecting the detectors (invisible to the naked eye). Source: rfidworld.com

Since the development of medical ultrasound imaging in the 1950s, the core technology of ultrasound detection has mainly focused on using piezoelectric detectors to convert the pressure generated by ultrasound into voltage. The resolution of ultrasound imaging depends on the size of the piezoelectric detector used. Reducing this size can achieve higher resolution and allow for smaller, more densely packed one-dimensional or two-dimensional ultrasound arrays, thus improving the ability to distinguish imaging tissue or material characteristics. However, further reducing the size of piezoelectric detectors greatly affects their sensitivity, making them unusable for practical applications.

1. Manufacturing optical ultrasonic detectors using computer chip technology

Silicon photonics technology is widely used to miniaturize optical components and densely package them on the small surface of a silicon chip. Although silicon does not exhibit any piezoelectric effect, its ability to confine light to dimensions smaller than the optical wavelength has been widely used in the development of miniature photonic circuits.

Researchers from the Helmholtz Zentrum München and the Technical University of Munich have leveraged the advantages of these miniaturized photonic circuits to design the world's smallest ultrasound detector—the silicon waveguide-etalon detector (SWED). Instead of recording the voltage of a piezoelectric crystal, SWED monitors changes in light intensity as it propagates through a miniaturized photonic circuit.

SWED developer Rami Shnaiderman said: "This is the first time that ultrasound has been detected using a detector smaller than a blood cell." "If a piezoelectric detector were miniaturized to the scale of SWED, its sensitivity would decrease by a factor of 100 million."

2. Super-resolution imaging

"Thanks to silicon photonics, we have been able to miniaturize the detector to an astonishing degree while maintaining high sensitivity." said Professor Vasilis Ntziachristos, head of the research team. The size of SWED is approximately 0.5 micrometers (=0.0005 millimeters). The corresponding area is at least 10,000 times smaller than the smallest piezoelectric detectors used in clinical imaging applications. The wavelength of SWED is also 200 times smaller than the ultrasound wavelength, meaning it can be used to observe features smaller than 1 micrometer, which is known as super-resolution imaging.

3. Low Price, High Functionality

Because this technology utilizes the robustness and ease of manufacturing of the silicon platform, large numbers of detectors can be produced at a fraction of the cost of piezoelectric detectors, making mass production possible. This is very important for developing different detection applications based on ultrasound. Shnaiderman added: "We will continue to optimize every parameter of this technology—sensitivity, integration of large arrays of SWEDs, and implementation in handheld devices and endoscopes."

4. Future Development and Applications

"The detector was initially developed to advance the performance of photoacoustic imaging, which is our main research direction; however, we can now foresee applications in a wider range of sensing and imaging fields." said Ntziachristos.

While the researchers' primary goal is application in clinical diagnostics and basic biomedical research, industrial applications may also benefit from this new technology. The improved imaging resolution can further investigate the details of tissues and materials. Currently, the first applications of this research involve super-resolution photoacoustic imaging of cells and microvasculature in tissues, but SWED can also be used to study the fundamental properties of ultrasound and its interaction with matter, which was previously impossible.

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