Researchers at the Max Planck Institute and the University of Stuttgart in Germany have developed a method to create high-resolution ultrasound fields, a capability which may improve the effectiveness of ultrasound therapies and tailor them for individual patients. The technique involves passing ultrasonic waves through water, where hydrogen bubbles help to transform the waves into desired shapes.
High-power ultrasound therapy is currently used to destroy tumor tissues, including prostate and uterine tumors. However, the technique can also damage healthy tissue, since it generates a great deal of heat, so the ultrasound field must be tightly controlled to restrict it to the tumor as much as possible. This is particularly difficult for brain tumors, as the skull distorts the field.
Current methods to control ultrasound fields involve creating several individual sound sources, which are then shifted to strengthen or weaken each other. However, this technique is limited and can only produce about 1,000 pixels. The newly invented approach, published in journal Nature Communications, can generate as many as 10,000 individual pixels.
“In order to modulate the sound pressure profile, we take advantage of the different acoustic properties of water and air,” said Zhichao Ma, a researcher involved in the study. “While an ultrasonic wave passes through a liquid unhindered, it is completely reflected by air bubbles”.
The researchers developed a thumbnail-sized chip on which they can split water to form hydrogen bubbles in a specific pattern. They can then send an ultrasonic wave through the chip, and when it encounters the bubbles it transforms to form a desired shape. Creating a different profile is as simple as wiping the hydrogen bubbles away and producing a different pattern.
“In this way, we can use much more powerful ultrasonic transducers”, said Kai Melde, another researcher involved in the study. “Thanks to a chip with 10,000 pixels that modulates the ultrasonic wave, we can generate a much finer-resolved profile.”