100 MHz for Clinical Ultrasound

The Engineer is reporting that a team of researchers from Edinburgh, Paisley and Birmingham Universities is working on a new higher frequency, and hence, higher resolution ultrasound technology.
Here’s the plan:

Existing ultra-high resolution systems are based on mechanically scanned, single-element transducers. These systems demonstrate the need for increased resolution, but at the same time limit progress because they cannot be used in real time.
The team will develop a technique to produce both ultra-high resolution and real-time images. Initially, the system will be based on single-element, mechanically- scanned transducers, but the project will move into a second phase and develop a multi-element, electronically scanned system, which will improve the uniformity of the scanning process. For this, ultrasound transducers are needed, which can operate at frequencies higher than the present maximum of 30MHz. The team propose to reach frequencies as high as 100MHz…
Ultrasound imaging is measured in millimetres and microns. Achieving 100MHZ frequencies should enable the team to reach the sub-millimetre range. McDicken [Dr. Norman McDicken from Edinburgh University -ed.] said: ‘When we look at the layers of a cavity wall we will be able to see much more detail at sub-millimetre range.
“Improved resolution helps with clarity of lines and boundary definitions. Users may be able to see boundaries they could not see before. We know these boundaries exist from looking at them histologically. If we can improve the imaging equipment we can start seeing these boundaries.”
To achieve ultra-high resolution, the team will reduce the size of piezocomposite material used in ultrasound transducers. Piezocomposites are widely used in underwater sonar and biomedical imaging, but the resolution of the images that can be obtained in medical applications is limited by the maximum frequency.
Usually, the higher the frequency the greater the attenuation. Where a high-resolution image is less important, attenuation is less of an issue. However, where an ultrahigh resolution is desirable – as it is in medical diagnostics – attenuation becomes a serious hurdle.
The maximum frequency is limited by the minimum size of piezocomposite, and the team is focusing on producing micron-scale components that have the dimensions of around 10 microns. To date, attempts to manufacture material with micron-scale dimensions have been unsuccessful. The smallest available is around 20 microns.
in the first instance the researchers will aim at halving the size of the piezocomposite dimensions. But they eventually hope to reduce the present size by a quarter, thus reaching ultra-high levels of frequency.
The three universities each have a discipline to develop. “Paisley translates Edinburgh’s clinical requirements into device design,” explained Paisley’s Prof Sandy Cochran. “Birmingham then works with Paisley to implement those designs and manufacture the piezocomposites. It is a very cohesive project,” she said.

Our guess is that if this technology makes it through, it will be only available for in vivo ultrasound: at such high frequencies, the ultrasound penetration is quite shallow. And it is a law of physics: hard to bypass that one!
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