An ultrasonic projector for medicine
A chip-based technology that modulates intensive sound pressure profiles
with high resolution opens up new possibilities for ultrasound therapy

Date:
October 19, 2020
Source:
Max-Planck-Gesellschaft
Summary:
A chip-based technology that modulates intensive sound pressure
profiles with high resolution opens up new possibilities for
ultrasound therapy.



FULL STORY ==========================================================================
A chip-based technology that generates sound profiles with high resolution
and intensity could create new options for ultrasound therapy, which
would become more effective and easier. A team of researchers led by Peer Fischer from the Max Planck Institute for Intelligent Systems and the University of Stuttgart has developed a projector that flexibly modulates three-dimensional ultrasound fields with comparatively little technical
effort. Dynamic sound pressure profiles can thus be generated with higher resolution and sound pressure than the current technology allows. It
should soon be easier to tailor ultrasound profiles to individual
patients. New medical applications for ultrasound may even emerge.


========================================================================== Ultrasound is widely used as a diagnostic tool in both medicine and
materials science. It can also be used therapeutically. In the US, for
example, tumours of the uterus and prostate are treated with high-power ultrasound. The ultrasound destroys the cancer cells by specific heating
of the diseased tissue. Researchers worldwide are using ultrasound to
combat tumours and other pathological changes in the brain. "In order
to avoid damaging healthy tissue, the sound pressure profile must be
precisely shaped," explains Peer Fischer, Research Group Leader at the Max Planck Institute for Intelligent Systems and professor at the University
of Stuttgart. Tailoring an intensive ultrasound field to diseased tissue
is somewhat more difficult in the brain. This is because the skullcap
distorts the sound wave. The Spatial Ultrasound Modulator (SUM) developed
by researchers in Fischer's group should help to remedy this situation
and make ultrasound treatment more effective and easier in other cases. It allows the three-dimensional shape of even very intense ultrasound waves
to be varied with high resolution -- and with less technical effort than
is currently required to modulate ultrasound profiles.

High intensity sound pressure profiles with 10,000 pixels Conventional
methods vary sound fields with several individual sound sources, the waves
of which can be superimposed and shifted against each other. However,
because the individual sound sources cannot be miniaturized at will,
the resolution of these sound pressure profiles is limited to 1000
pixels. The sound transmitters are then so small that the sound pressure
is sufficient for diagnostic but not therapeutic purposes. With the new technology, the researchers first generate an ultrasonic wave and then
modulate its sound pressure profile independently, essentially killing
two birds with one stone.

"In this way, we can use much more powerful ultrasonic transducers,"
explains postdoctoral fellow Kai Melde, who is part of the team that
developed the SUM.

"Thanks to a chip with 10,000 pixels that modulates the ultrasonic
wave, we can generate a much finer-resolved profile." "In order to
modulate the sound pressure profile, we take advantage of the different acoustic properties of water and air," says Zhichao Ma, a post- doctoral
fellow in Fischer's group, who was instrumental in developing the
new SUM technology: "While an ultrasonic wave passes through a liquid unhindered, it is completely reflected by air bubbles." The research team
from Stuttgart thus constructed a chip the size of a thumbnail on which
they can produce hydrogen bubbles by electrolysis (i.e. the splitting of
water into oxygen and hydrogen with electricity) on 10,000 electrodes
in a thin water film. The electrodes each have an edge length of less
than a tenth of a millimetre and can be controlled individually.

A picture show with ultrasound If you send an ultrasonic wave through
the chip with a transducer (a kind of miniature loudspeaker), it passes
through the chip unhindered. But as soon as the sound wave hits the
water with the hydrogen bubbles, it continues to travel only through the liquid. Like a mask, this creates a sound pressure profile with cut-outs
at the points where the air bubbles are located. To form a different
sound profile, the researchers first wipe the hydrogen bubbles away from
the chip and then generate gas bubbles in a new pattern.

The researchers demonstrated how precisely and variably the new projector
for ultrasound works by writing the alphabet in a kind of picture show
of sound pressure profiles. To make the letters visible, they caught micro-particles in the various sound pressure profiles. Depending on
the sound pattern, the particles arranged themselves into the individual letters.

Organoid models for drug testing For similar images, the scientists collaborating with Peer Fischer, Kai Melde, and Zhichao Ma previously
arranged micro-particles with sound pressure profiles, which they modelled using a slightly different technique. They used special plastic stencils
to deform the pressure profile of an ultrasonic wave like a hologram and arrange small particles -- as well as biological cells in a liquid --
into a desired pattern. However, the plastic holograms only provided
still images. For each new pattern, they had to make a different plastic template. Using the ultrasound projector, the Stuttgart team is able to generate a new sound profile in about 10 seconds. "With other chips,
we could significantly increase the frame rate," says Kai Melde, who
led the hologram development team.

The technique could be used not only for diagnostic and therapeutic
purposes but also in biomedical laboratories. For example, to arrange
cells into organoid models. "Such organoids enable useful tests of active pharmaceutical ingredients and could therefore at least partially replace animal experiments," says Fischer.


========================================================================== Story Source: Materials provided by Max-Planck-Gesellschaft. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Zhichao Ma, Kai Melde, Athanasios G. Athanassiadis, Michael Schau,
Harald
Richter, Tian Qiu, Peer Fischer. Spatial ultrasound modulation by
digitally controlling microbubble arrays. Nature Communications,
2020; 11 (1) DOI: 10.1038/s41467-020-18347-2 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201019125522.htm

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